U.S. patent application number 12/090467 was filed with the patent office on 2009-12-03 for surface-emitting laser array, optical scanning device, and image forming device.
This patent application is currently assigned to RICOH COMPANY, LTD.. Invention is credited to Akihiro Itoh, Shunichi Sato, Hiroyoshi Shouji, Satoru Sugawara.
Application Number | 20090295902 12/090467 |
Document ID | / |
Family ID | 38544150 |
Filed Date | 2009-12-03 |
United States Patent
Application |
20090295902 |
Kind Code |
A1 |
Sato; Shunichi ; et
al. |
December 3, 2009 |
SURFACE-EMITTING LASER ARRAY, OPTICAL SCANNING DEVICE, AND IMAGE
FORMING DEVICE
Abstract
A surface-emitting laser array includes a plurality of
surface-emitting laser elements. Each surface-emitting laser
element includes a first reflection layer formed on a substrate, a
resonator formed in contact with the first reflection layer and
containing an active layer, and a second reflection layer formed
over the first reflection layer and in contact with the resonator.
The second reflection layer contains a selective oxidation layer.
The first reflection layer contains on the active layer side at
least a low refractive index layer having an oxidation rate
equivalent to or larger than an oxidation rate of a selective
oxidation layer contained in the second reflection layer. The
resonator is made of an AlGaInPAs base material containing at least
In. A bottom of a mesa structure is located under the selective
oxidation layer and over the first reflection layer.
Inventors: |
Sato; Shunichi; (Miyagi,
JP) ; Itoh; Akihiro; (Miyagi, JP) ; Sugawara;
Satoru; (Miyagi, JP) ; Shouji; Hiroyoshi;
(Miyagi, JP) |
Correspondence
Address: |
COOPER & DUNHAM, LLP
30 Rockefeller Plaza, 20th Floor
NEW YORK
NY
10112
US
|
Assignee: |
RICOH COMPANY, LTD.
Tokyo
JP
|
Family ID: |
38544150 |
Appl. No.: |
12/090467 |
Filed: |
August 20, 2007 |
PCT Filed: |
August 20, 2007 |
PCT NO: |
PCT/JP2007/066508 |
371 Date: |
April 16, 2008 |
Current U.S.
Class: |
347/224 ;
257/E21.002; 372/24; 372/50.11; 372/50.124; 438/34 |
Current CPC
Class: |
H01S 5/2213 20130101;
H01S 5/423 20130101; H01S 5/3434 20130101; H01S 5/18358 20130101;
H01S 5/18313 20130101; H01S 2302/00 20130101; B82Y 20/00 20130101;
H01S 5/18 20130101; H01S 5/0203 20130101 |
Class at
Publication: |
347/224 ;
372/50.124; 372/24; 372/50.11; 438/34; 257/E21.002 |
International
Class: |
B41J 2/435 20060101
B41J002/435; H01S 5/183 20060101 H01S005/183; H01S 3/10 20060101
H01S003/10; H01S 5/187 20060101 H01S005/187; H01L 21/00 20060101
H01L021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 23, 2006 |
JP |
2006-226561 |
Aug 23, 2006 |
JP |
2006-226562 |
May 22, 2007 |
JP |
2007-134856 |
Claims
1. A surface-emitting laser array including a plurality of
surface-emitting laser elements, each of the plurality of
surface-emitting laser elements comprising: a first reflection
layer formed on a substrate to constitute a semiconductor Bragg
reflector; a resonator formed in contact with the first reflection
layer and containing an active layer; and a second reflection layer
formed over the first reflection layer and in contact with the
resonator to constitute the semiconductor Bragg reflector, the
second reflection layer containing a selective oxidation layer
therein, wherein the first reflection layer contains on the active
layer side at least a low refractive index layer having an
oxidation rate equivalent to or larger than an oxidation rate of a
selective oxidation layer contained in the second reflection layer,
the resonator is made of an AlGaInPAs base material containing at
least In, and a bottom of a mesa structure in each surface-emitting
laser element is located under the selective oxidation layer and
over the first reflection layer.
2. The surface-emitting laser array of claim 1, wherein the
resonator has an etching rate smaller than an etching rate of the
second reflection layer.
3. The surface-emitting laser array of claim 1, wherein the second
reflection layer containing on the active layer side a layer made
of the AlGaInPAs base material containing at least In.
4. The surface-emitting laser array of claim 1, wherein the bottom
of the mesa structure is located inside the resonator or at an
interface between the second reflection layer and the
resonator.
5. The surface-emitting laser array of claim 1, wherein the first
reflection layer contains the low refractive index layer, which is
made of AlAs, over an entire area of the surface-emitting laser
element.
6. The surface-emitting laser array of claim 1, wherein the
selective oxidation layer contained in the second reflection layer
constitutes a selective oxidation type current narrowing
portion.
7. The surface-emitting laser array of claim 1, wherein a
difference between an etching depth in an inter-element gap of the
plurality of surface-emitting laser elements and an etching depth
of a peripheral portion of the plurality of surface-emitting laser
elements is equal to or smaller than 1/2 of a beam-emission
wavelength of each surface-emitting laser element.
8. The surface-emitting laser array of claim 7, wherein the
inter-element gap between two adjacent ones of the plurality of
surface-emitting laser elements is set to a smaller one of a gap
between top surface positions of two mesa structures in the
plurality of surface-emitting laser elements and a gap between
bottom surface positions of the two mesa structures, and is equal
to or smaller than 20 micrometers.
9. The surface-emitting laser array of claim 1, wherein a side of
the first reflection layer is covered by a protection film.
10. The surface-emitting laser array of claim 9, wherein the
protection film is made of any of SiO.sub.2, SiN and SiON.
11. The surface-emitting laser array of claim 1, wherein a content
of aluminum of the low refractive index layer arranged on the
resonator side of the first reflection layer is larger than a
content of aluminum of the selective oxidation layer.
12. The surface-emitting laser array of claim 1, wherein a content
of aluminum of a low refractive index layer arranged on the
resonator side of the first reflection layer is the same as a
content of aluminum of the selective oxidation layer, and a
thickness of the low refractive index layer arranged on the
resonator side of the first reflection layer is larger than a
thickness of the selective oxidation layer.
13. An optical scanning device comprising: the surface-emitting
laser array according to claim 1; a deflection unit deflecting a
plurality of laser beams emitted by the surface-emitting laser
array, and a scanning optical element drawing the laser beams from
the deflection unit on a scanned surface of a photoconductor.
14. An image forming device in which the optical scanning device
according to claim 13 is provided.
15. An image forming device in which the surface-emitting laser
array according to claim 1 is provided as a light source emitting a
plurality of laser beams.
16. A surface-emitting laser element having a mesa structure which
emits a laser beam, comprising: a substrate; a first reflection
layer formed on the substrate to constitute a semiconductor Bragg
reflector; a resonator formed in contact with the first reflection
layer and containing an active layer; a second reflection layer
formed in contact with the resonator to constitute the
semiconductor Bragg reflector; and an absorption layer arranged to
absorb a difference of an etching depth in an in-surface direction
of the substrate when forming the mesa structure, wherein a bottom
of the mesa structure is located in the absorption layer in a
direction perpendicular to the substrate, and the absorption layer
is formed in at least a part of the resonator in a thickness
direction of the resonator.
17. The surface-emitting laser element of claim 16, wherein the
absorption layer is formed in an entire area of the resonator in a
thickness direction of the resonator.
18. The surface-emitting laser element of claim 16, wherein the
absorption layer is formed in an entire area of the resonator in a
thickness direction of the resonator and formed partially in a
thickness direction of the second reflection layer.
19. The surface-emitting laser element of claim 16, wherein the
absorption layer contains at least In.
20. A method of manufacturing a surface-emitting laser array, the
surface-emitting laser array including: an element-arrangement
portion provided on a substrate and having a plurality of
surface-emitting laser elements arranged; and a flat part provided
on the substrate and arranged in a circumference of the
element-arrangement portion in an in-surface direction of the
substrate, each of the plurality of surface-emitting laser elements
including a mesa structure which emits a laser beam, and the flat
part and the element-arrangement portion including an absorption
layer arranged to absorb a difference of an etching depth in the
in-surface direction when forming the mesa structure, the method
comprising the steps of: forming a multilayer semiconductor film on
the substrate; and etching the multilayer semiconductor film to
cause a bottom of the mesa structure to be located in the
absorption layer, so that the element-arrangement portion and the
flat part are formed.
Description
TECHNICAL FIELD
[0001] This invention relates to a surface-emitting laser array, an
optical scanning device including the surface-emitting laser array,
and an image forming device including the surface-emitting laser
array.
BACKGROUND ART
[0002] In a surface-emitting laser array in which surface-emitting
laser elements are integrated, the output of each surface-emitting
laser element during operation may decline due to a temperature
rise through reception of heat from the surrounding
surface-emitting laser elements, and the life of the
surface-emitting laser array may be shortened.
[0003] To obviate the problem, it is necessary to improve the heat
dissipation characteristic. For example, a material having a high
thermal conductivity should be used for a semiconductor Bragg
reflector which is located on the side of main heat dissipation.
Among the materials which can be used for a semiconductor Bragg
reflector of a surface-emitting laser element on a GaAs substrate,
AlAs is a suitable one that has the highest thermal
conductivity.
[0004] However, there is a case in which etching into the shape of
a mesa structure is performed in order to separate the
surface-emitting laser element from the surrounding part
electrically or spatially. In this case, although it is unnecessary
that the etching reaches the lower semiconductor Bragg reflector
arranged on the substrate side, the design is carried out, from the
problem of the controllability of etching, by assuming that the
etching bottom reaches the lower semiconductor Bragg reflector.
[0005] For example, in the case of an oxidization type
surface-emitting laser element, it is necessary to etch more deeply
than a selective oxidation layer in order to perform selective
oxidation. For the purpose of stopping the divergence of the
current, it is common to arrange the selective oxidation layer at a
place near the active layer of the p-type semiconductor Bragg
reflector (or the semiconductor Bragg reflector arranged above the
active layer), or in the position of the first to fifth nodes
(nodes in the field strength distribution of a laser beam) from the
active layer.
[0006] However, from the problem of the controllability of the
etching depth, it is difficult to control the etching bottom to be
deeper than the selective oxidation layer but not to reach the
lower semiconductor Bragg reflector.
[0007] In order to control the etching depth in the whole wafer
surface, it is necessary to not only control the etching time but
also attain the uniformity of etching in the wafer surface, and the
uniformity of distribution of thickness of the crystal growth
layer. Practically, it is very difficult to carry out mesa etching
so as be deeper than the selective oxidation layer but not to reach
the lower semiconductor Bragg reflector.
[0008] To resolve the problem, Japanese Laid-Open Patent
Application No. 2002-164621 discloses separating the lower
semiconductor Bragg reflector into two layers. In the laser array
of Japanese Laid-Open Patent Application No. 2002-164621, the
substrate side one of the two lower semiconductor Bragg reflector
layers is a main refractive index layer which is made of AlAs. AlAs
has a thermal conductivity which is much larger than that of
AlGaAs. On the other hand, the active-layer-side reflector layer is
made of AlGaAs which is used conventionally.
[0009] However, in the case of the surface-emitting laser array,
carrying out uniform mesa etching within the surface of the wafer
is still more difficult for other additional reasons. If the
inter-element gap of the surface-emitting laser elements is
narrowed in order to carry out array arrangement with high density,
a difference .DELTA.d between an etching depth of the inter-element
gap and an etching depth of the flat part in the circumference of
the surface-emitting laser array becomes large. Furthermore, a
skirt portion arises in the etching configuration. It is desirable
that the selective oxidation layer does not start from the skirt
portion, in order to control the oxidization narrowing dimensions
strictly.
[0010] However, if etching is performed so that the selective
oxidation layer may not start from the skirt portion, the etching
bottom in the flat part in the circumference of the
surface-emitting laser array enters the lower semiconductor Bragg
reflector.
[0011] Since the low refractive index layer of the lower
semiconductor Bragg reflector usually is larger in thickness than
the selective oxidation layer, if both the layers have the same
composition, the oxidation rate of the low refractive index layer
is quicker than that of the selective oxidation layer.
[0012] If the oxidation rate of the low refractive index layer of
the lower semiconductor Bragg reflector is quicker than the
selective oxidation layer, the whole low refractive index layer is
oxidized early and performing the current pouring is
impossible.
[0013] To avoid the problem, AlAs cannot be used as a material of
the low refractive index layer which is located near the active
layer of the lower semiconductor Bragg reflector. For this reason,
in order to decrease the oxidation rate of the semiconductor Bragg
reflector, it has been necessary to use AlGaAs in which a certain
amount of Ga is added (for example, Al.sub.0.9Ga.sub.0.1As). Refer
to the Technical Report CS-3-4 (2004) from the Institute of
Electronics, Information and Communication Engineers, Electronics
Society Convention, and IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 11,
No. 12, 1999, pp. 1539-1541.
[0014] Japanese Laid-Open Patent Application No. 09-018093
discloses that etching of the upper semiconductor Bragg reflector
is stopped up to a GaInP cladding layer (resonator region).
[0015] FIG. 37 is a plan view of a surface-emitting laser array
according to the related art. As shown in FIG. 37, the double dummy
elements are arranged in the circumference of the central array
part where the surface-emitting laser elements are arranged.
[0016] Japanese Laid-Open Patent Application No. 2000-114656
discloses that the post (mesa) in the central array part and the
post (mesa) in the circumference of the array part are subjected to
a different environment and the posts (mesa) have a different
configuration accordingly.
[0017] And Japanese Laid-Open Patent Application No. 2000-114656
discloses a surface-emitting laser array in which the double dummy
elements arranged in the circumference of the central array part
allows uniform characteristics.
[0018] In a conventional oxidization type surface-emitting laser
array, the etching bottom in the flat part in the circumference of
the surface-emitting laser array faces the lower semiconductor
Bragg reflector. A material having a high thermal conductivity,
such as AlAs, is easily oxidized if it appears on the surface by
etching. AlAs cannot be used for the lower semiconductor Bragg
reflector (at least in the region near the active layer).
[0019] Therefore, heat is easily accumulated in the active layer
and the temperature of the active layer increases. There are the
problems that the optical output declines and the life of the
surface-emitting laser element becomes short. Especially, when the
surface-emitting laser array operates, undesired influences due to
thermal interference become remarkable.
[0020] Operation of the surface-emitting laser array at high
current values is impossible and use of the surface-emitting laser
array with a low optical output is unavoidable. And the life of the
surface-emitting laser array becomes short due to a temperature
rise caused by thermal interference.
[0021] According to the teaching of Japanese Laid-Open Patent
Application No. 2000-114656, in order to keep the etching bottom in
the flat part in the circumference of the laser array from reaching
the lower semiconductor Bragg reflector, the dummy elements may be
arranged in the whole wafer to make small the difference .DELTA.d
between the etching depth in the central array part and the etching
depth in the flat part in the circumference of the array part.
[0022] If the flat part is not eliminated, the etching bottom
reaches the lower semiconductor Bragg reflector so that AlAs is
oxidized. Thus, it is necessary to arrange the dummy elements in
the whole wafer.
[0023] However, if the dummy elements are arranged in the whole
wafer, the area which is to be etched is decreased. This causes
monitoring of oxidization (plasma emission spectrometry, optical
reflective index analysis, etc.) to be difficult to perform.
Moreover, if the dummy elements are arranged in the whole wafer,
unevenness appears on the surface of the laser array and the
probability of wire cut-off is raised. Furthermore, it is needed to
form the wire bonding pads for implementation. However, if
unevenness exists under the bottom of the bonding pads, the mesa
structure may be damaged at the time of wire bonding, which causes
a faulty surface-emitting laser array to be produced.
DISCLOSURE OF THE INVENTION
[0024] According to one aspect of the invention, there is provided
an improved surface-emitting laser array in which the
above-described problems are eliminated.
[0025] According to one aspect of the invention there is provided a
surface-emitting laser array which is arranged without using dummy
elements so that heat is not easily accumulated in the active
layer.
[0026] According to one aspect of the invention there is provided
an optical scanning device including a surface-emitting laser array
which is arranged without using dummy elements so that heat is not
easily accumulated in the active layer.
[0027] According to one aspect of the invention, there is provided
an image forming device including a surface-emitting laser array
which is arranged without using dummy elements so that heat is not
easily accumulated in the active layer.
[0028] In an embodiment of the invention which solves or reduces
one or more of the above-mentioned problems, there is provided a
surface-emitting laser array including a plurality of
surface-emitting laser elements, each of the plurality of
surface-emitting laser elements comprising: a first reflection
layer formed on a substrate to constitute a semiconductor Bragg
reflector; a resonator formed in contact with the first reflection
layer and containing an active layer; and a second reflection layer
formed over the first reflection layer and in contact with the
resonator to constitute the semiconductor Bragg reflector, the
second reflection layer containing a selective oxidation layer
therein, wherein the first reflection layer contains on the active
layer side at least a low refractive index layer having an
oxidation rate equivalent to or larger than an oxidation rate of a
selective oxidation layer contained in the second reflection layer,
the resonator is made of an AlGaInPAs base material containing at
least In, and a bottom of a mesa structure in each surface-emitting
laser element is located under the selective oxidation layer and
over the first reflection layer.
[0029] The above-mentioned surface-emitting laser array may be
configured so that the resonator has an etching rate smaller than
an etching rate of the second reflection layer.
[0030] The above-mentioned surface-emitting laser array may be
configured so that the second reflection layer containing on the
active layer side a layer made of the AlGaInPAs base material
containing at least In.
[0031] The above-mentioned surface-emitting laser array may be
configured so that the bottom of the mesa structure is located
inside the resonator or at an interface between the second
reflection layer and the resonator.
[0032] The above-mentioned surface-emitting laser array may be
configured so that the first reflection layer contains the low
refractive index layer, which is made of AlAs, over an entire area
of the surface-emitting laser element.
[0033] The above-mentioned surface-emitting laser array may be
configured so that the selective oxidation layer contained in the
second reflection layer constitutes a selective oxidation type
current narrowing portion.
[0034] The above-mentioned surface-emitting laser array may be
configured so that a difference between an etching depth in an
inter-element gap of the plurality of surface-emitting laser
elements and an etching depth of a peripheral portion of the
plurality of surface-emitting laser elements is equal to or smaller
than 1/2 of a beam-emission wavelength of each surface-emitting
laser element.
[0035] The above-mentioned surface-emitting laser array may be
configured so that the inter-element gap between two adjacent ones
of the plurality of surface-emitting laser elements is set to a
smaller one of a gap between top surface positions of two mesa
structures in the plurality of surface-emitting laser elements and
a gap between bottom surface positions of the two mesa structures,
and is equal to or smaller than 20 micrometers.
[0036] The above-mentioned surface-emitting laser array may be
configured so that a side of the first reflection layer is covered
by a protection film.
[0037] The above-mentioned surface-emitting laser array may be
configured so that the protection film is made of any of SiO.sub.2,
SiN and SiON.
[0038] The above-mentioned surface-emitting laser array may be
configured so that a content of aluminum of the low refractive
index layer arranged on the resonator side of the first reflection
layer is larger than a content of aluminum of the selective
oxidation layer.
[0039] The above-mentioned surface-emitting laser array may be
configured so that a content of aluminum of a low refractive index
layer arranged on the resonator side of the first reflection layer
is the same as a content of aluminum of the selective oxidation
layer, and a thickness of the low refractive index layer arranged
on the resonator side of the first reflection layer is larger than
a thickness of the selective oxidation layer.
[0040] In an embodiment of the invention which solves or reduces
one or more of the above-mentioned problems, there is provided an
optical scanning device comprising: the above-mentioned
surface-emitting laser array; a deflection unit deflecting a
plurality of laser beams emitted by the surface-emitting laser
array, and a scanning optical element drawing the laser beams from
the deflection unit on a scanned surface of a photoconductor.
[0041] In an embodiment of the invention which solves or reduces
one or more of the above-mentioned problems, there is provided an
image forming device in which the above-mentioned optical scanning
device is provided.
[0042] In an embodiment of the invention which solves or reduces
one or more of the above-mentioned problems, there is provided an
image forming device in which the above-mentioned surface-emitting
laser array is provided as a light source emitting a plurality of
laser beams.
[0043] In an embodiment of the invention which solves or reduces
one or more of the above-mentioned problems, there is provided a
surface-emitting laser element having a mesa structure which emits
a laser beam, the surface-emitting laser element comprising: a
substrate; a first reflection layer formed on the substrate to
constitute a semiconductor Bragg reflector; a resonator formed in
contact with the first reflection layer and containing an active
layer; a second reflection layer formed in contact with the
resonator to constitute the semiconductor Bragg reflector; and an
absorption layer arranged to absorb a difference of an etching
depth in an in-surface direction of the substrate when forming the
mesa structure, wherein a bottom of the mesa structure is located
in the absorption layer in a direction perpendicular to the
substrate, and the absorption layer is formed in at least a part of
the resonator in a thickness direction of the resonator.
[0044] The above-mentioned surface-emitting laser element may be
configured so that the absorption layer is formed in an entire area
of the resonator in a thickness direction of the resonator.
[0045] The above-mentioned surface-emitting laser element may be
configured so that the absorption layer is formed in an entire area
of the resonator in a thickness direction of the resonator and
formed partially in a thickness direction of the second reflection
layer.
[0046] The above-mentioned surface-emitting laser element may be
configured so that the absorption layer contains at least In.
[0047] In an embodiment of the invention which solves or reduces
one or more of the above-mentioned problems, there is provided a
method of manufacturing a surface-emitting laser array, the
surface-emitting laser array including: an element-arrangement
portion provided on a substrate and having a plurality of
surface-emitting laser elements arranged; and a flat part provided
on the substrate and arranged in a circumference of the
element-arrangement portion in an in-surface direction of the
substrate, each of the plurality of surface-emitting laser elements
including a mesa structure which emits a laser beam, and the flat
part and the element-arrangement portion including an absorption
layer arranged to absorb a difference of an etching depth in the
in-surface direction when forming the mesa structure, the method
comprising the steps of: forming a multilayer semiconductor film on
the substrate; and etching the multilayer semiconductor film to
cause a bottom of the mesa structure to be located in the
absorption layer, so that the element-arrangement portion and the
flat part are formed.
[0048] According to embodiments of the surface-emitting laser array
of the invention, it is possible to. In each of the
surface-emitting laser elements, which constitute the
surface-emitting laser array, the resonator is made of the material
containing at least In, the bottom of the mesa structure is
arranged so that the second reflection layer is nearer to the
bottom of the mesa structure than the first reflection layer, and
the first reflection layer contains on the active layer side at
least a low refractive index layer having an oxidation rate
equivalent to or larger than an oxidation rate of the selective
oxidation layer.
[0049] And in the process of forming the mesa structure, the
difference between the etching depth in the array region where the
surface-emitting laser elements are arranged and the etching depth
in the circumference of the array region is reduced to prevent
exposure of the first reflection layer in the circumference of the
array region and prevent oxidization of the first reflection layer.
As a result, heat generated in the active layer radiates easily to
the substrate side via the first reflection layer. Therefore,
according to the invention, it is possible to arrange the
surface-emitting laser array without using dummy elements so that
heat is not easily accumulated in the active layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0050] Other objects, features and advantages of the present
invention will be apparent from the following detailed description
when reading in conjunction with the accompanying drawings.
[0051] FIG. 1 is a plan view of a surface-emitting laser array in
an embodiment of the invention.
[0052] FIG. 2 is a cross-sectional view of a surface-emitting laser
element in the surface-emitting laser array of FIG. 1.
[0053] FIG. 3 is a cross-sectional view showing the neighborhood of
an active layer of the surface-emitting laser element of FIG.
2.
[0054] FIG. 4A, FIG. 4B, and FIG. 4C are diagrams for explaining a
method of manufacturing the surface-emitting laser array of FIG.
1.
[0055] FIG. 5A, FIG. 5B, and FIG. 5C are diagram for explaining the
method of manufacturing the surface-emitting laser array of FIG.
1.
[0056] FIG. 6A and FIG. 6B are diagrams for explaining the method
of manufacturing the surface-emitting laser array of FIG. 1.
[0057] FIG. 7 is a diagram for explaining etching in the process of
FIG. 4B.
[0058] FIG. 8 is a timing chart for explaining a plasma emission at
the time of etching when producing the surface-emitting laser array
of FIG. 1.
[0059] FIG. 9 is a timing chart for explaining a plasma emission at
the time of etching when producing the surface-emitting laser array
of FIG. 1.
[0060] FIG. 10 is a diagram for explaining an etching depth in the
flat part at the time of stopping etching in the resonator region,
and a difference between an etching depth in the inter-element gap
of the surface-emitting laser elements and an etching depth in the
flat part with respect to a mesa interval.
[0061] FIG. 11 is a diagram for explaining an etching depth in the
flat part at the time of stopping etching in the reflection layer
arranged on the substrate side, and a difference between an etching
depth in the inter-element gap of the surface-emitting laser
elements and an etching depth in the flat part with respect to a
mesa interval.
[0062] FIG. 12 is a plan view and cross-sectional view of the
surface-emitting laser array of FIG. 1.
[0063] FIG. 13 is a plan view of a surface-emitting laser array in
an embodiment of the invention.
[0064] FIG. 14 is a plan view of a surface-emitting laser array in
an embodiment of the invention.
[0065] FIG. 15 is a cross-sectional view of a surface-emitting
laser element in the surface-emitting laser array of FIG. 14.
[0066] FIG. 16 is a cross-sectional view showing the neighborhood
of an active layer of the surface-emitting laser element of FIG.
15.
[0067] FIG. 17 is a cross-sectional view of the surface-emitting
laser element in the embodiment of FIG. 14 used for an
experiment.
[0068] FIG. 18 is a cross-sectional view of a surface-emitting
laser element in a comparative example used for an experiment.
[0069] FIG. 19 is a diagram for explaining the relationship between
the optical output and the current which show an experimental
result.
[0070] FIG. 20 is a plan view of a surface-emitting laser array in
an embodiment of the invention.
[0071] FIG. 21A, FIG. 21B, FIG. 21C, and FIG. 21D are diagrams for
explaining a method of manufacturing a surface-emitting laser array
in an embodiment of the invention.
[0072] FIG. 22A, FIG. 22B, FIG. 22C, and FIG. 22D are diagrams for
explaining a method of manufacturing the surface-emitting laser
array in this embodiment.
[0073] FIG. 23 is a diagram for explaining a method of
manufacturing the surface-emitting laser array of this
embodiment.
[0074] FIG. 24 is a diagram for explaining the surface-emitting
laser array of this embodiment.
[0075] FIG. 25 is a diagram showing the composition of an optical
scanning device using the surface-emitting laser array of FIG.
13.
[0076] FIG. 26 is a diagram showing the composition of a laser
printer.
[0077] FIG. 27 is a diagram showing the composition of an image
forming device.
[0078] FIG. 28 is a diagram of an optical transmitting module.
[0079] FIG. 29 is a cross-sectional view of a modification of the
surface-emitting laser element in the surface-emitting laser array
of FIG. 1.
[0080] FIG. 30 is a cross-sectional view showing the neighborhood
of the active layer of the surface-emitting laser element of FIG.
29.
[0081] FIG. 31 is a cross-sectional view of a modification of the
surface-emitting laser element in the surface-emitting laser array
of FIG. 1.
[0082] FIG. 32 is a cross-sectional view showing the neighborhood
of the active layer of the surface-emitting laser element of FIG.
31.
[0083] FIG. 33 is a cross-sectional view of a modification of the
surface-emitting laser element in the surface-emitting laser array
of FIG. 1.
[0084] FIG. 34 is a cross-sectional view showing the neighborhood
of the active layer of the surface-emitting laser element of FIG.
33.
[0085] FIG. 35 is a cross-sectional view of a modification of the
surface-emitting laser element in the surface-emitting laser array
of FIG. 1.
[0086] FIG. 36 is a cross-sectional view showing the neighborhood
of the active layer of the surface-emitting laser element of FIG.
35.
[0087] FIG. 37 is a plan view of a surface-emitting laser array
according to the related art.
BEST MODE FOR CARRYING OUT THE INVENTION
[0088] A description will be given of embodiments of the invention
with reference to the accompanying drawings.
[0089] FIG. 1 is a plan view of a surface-emitting laser array in
an embodiment of the invention. As shown in FIG. 1, the
surface-emitting laser array 100 of this embodiment includes
surface-emitting laser elements 1-32, pads 51-82, and wires
W1-W32.
[0090] The surface-emitting laser elements 1-32 are arranged in the
two-dimensional formation of four rows.times.eight columns. Each of
the surface-emitting laser elements 1-32 has the rectangle form
whose one side is 16 micrometers.
[0091] And the columns of four surface-emitting laser elements 1,
9, 17, 25/2, 10, 18, 26/3, 11, 19, 27/4, 12, 20, 28/5, 13, 21,
29/6, 14, 22, 30/7, 15, 23, 31/8, 16, 24, 32 are arranged in the
sub-scanning direction. And the rows of eight surface-emitting
laser elements 1-8/9-16/17-24/25-32 are arranged in the main
scanning direction.
[0092] The rows of the eight surface-emitting laser elements
1-8/9-16/17-24/25-32 arranged in the main scanning direction are
shifted in a step-wise manner in the sub-scanning direction, and
they are arranged so that 32 laser beams emitted from the 32
surface-emitting laser elements 1-32 do not overlap mutually. In
the eight surface-emitting laser elements 1-8/9-16/17-24/25-32
arranged in the main scanning direction, the gap between two
adjoining surface-emitting laser elements is set to an interval X.
In the four surface-emitting laser elements 1, 9, 17, 25/2, 10, 18,
26/3, 11, 19, 27/4, 12, 20, 28/5, 13, 21, 29/6, 14, 22, 30/7, 15,
23, 31/8, 16, 24, 32 arranged in the sub-scanning direction, the
gap between two adjoining surface-emitting laser elements is set to
an interval d. The interval d is smaller than the interval X.
[0093] For example, the interval d is equal to 24 micrometers and
the interval X is equal to 30 micrometers.
[0094] Eight normals taken from the centers of the eight
surface-emitting laser elements 1-8 arranged in the main scanning
direction, to the straight line parallel to the sub-scanning
direction are arranged in the sub-scanning direction at equal
intervals of c1, which is determined by the condition c1=d/8.
Namely, when the interval d is set to 24 micrometers, the interval
c1 is equal to 24/8=3 micrometers.
[0095] The eight normals taken from the respective centers of the
other eight surface-emitting laser elements 9-16/17-24/25-32
arranged in the main scanning direction, to the straight line
parallel to in the sub-scanning direction are also arranged in the
sub-scanning direction at equal intervals of c1.
[0096] The pads 51-82 are arranged around the circumference of the
surface-emitting laser elements 1-32 in two-dimensional formation.
The wires W1-W32 are arranged to connect the surface-emitting laser
elements 1-32 to the pads 51-82, respectively. And each of the
wires W1-W32 has a line width of 8 micrometers, for example.
[0097] The wires W1-W9, W16, W17, W24-W32 which connect the
surface-emitting laser elements 1-8, 9, 16, 17, 24-32 arranged in
the outermost circumference among the surface-emitting laser
elements 1-32 arranged in two dimensional formation, to the pads
51-59, 66, 67, 74, 75-82 respectively are arranged without passing
by between two adjoining surface-emitting laser elements in the
main scanning direction.
[0098] The wires W10-Wl5, W18-W23 which connect the
surface-emitting laser elements 10-15, 18-23 arranged in the inside
position among the surface-emitting laser elements 1-32 arranged in
two dimensional formation, to the pads 60-65, 68-73 respectively
are arranged so that they pass by between two adjoining
surface-emitting laser elements in the main scanning direction.
[0099] In the eight surface-emitting laser elements
1-8/9-16/17-24/25-32 arranged in the main scanning direction, the
gap between two adjoining surface-emitting laser elements is set to
the interval X (=30 micrometers) mentioned above. Each of the
surface-emitting laser elements 1-32 has a rectangular form one
side of which is equal to 16 micrometers. The interval between two
adjoining surface-emitting laser elements in the main scanning
direction is equal to 14 (=30-16) micrometers. The wires W10-W15,
W18-W23 the line width of which is 8 micrometers can be arranged
between two adjoining surface-emitting laser elements in the main
scanning direction.
[0100] FIG. 2 is a cross-sectional view of a surface-emitting laser
element 1 in the surface-emitting laser array of FIG. 1. As shown
in FIG. 2, the surface-emitting laser element 1 includes substrate
101, reflection layers 102,106, resonator spacer layers 103,105,
active layer 104, selective oxidation layer 107, contact layer 108,
SiO.sub.2 layer 109, insulating resin 110, p-type electrode 111,
and n-type electrode 112.
[0101] The surface-emitting laser element 1 is a surface-emitting
laser which emits a laser beam having a wavelength of 780 nm. The
substrate 101 is constituted by n-type gallium arsenide
(n-GaAs).
[0102] The reflection layer 102 is constituted by 40.5 cycles of
n-AlAs/n-Al.sub.0.3Ga.sub.0.7As where one cycle is a pair of n-AlAs
layer and n-Al.sub.0.3Ga.sub.0.7As layer, and formed on the
substrate 101.
[0103] And each thickness of n-AlAs and n-Al0.3Ga0.7As is set to
.lamda./4n (where n is a refractive index of each semiconductor
layer), when the emission wavelength of the surface-emitting laser
element 1 is set to .lamda..
[0104] The resonator spacer layer 103 is constituted by non-doped
(Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P and formed on the
reflection layer 102. The active layer 104 has the quantum well
structure containing the well layer constituted by GaInPAs and the
barrier layer constituted by Ga.sub.0.6In.sub.0.4P, and formed on
the resonator spacer layer 103.
[0105] The resonator spacer layer 105 is constituted by non-doped
(Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P, and formed on the active
layer 104. Assuming that a pair of
p-Al.sub.0.9Ga.sub.0.1As/Al.sub.0.3Ga.sub.0.7As is one cycle, the
reflection layer 106 is constituted by 24 cycles of
p-Al.sub.0.9Ga.sub.0.1As/Al.sub.0.3Ga.sub.0.7As, and formed on the
resonator spacer layer 105.
[0106] And the thickness of each of p-Al.sub.0.9Ga.sub.0.1As and
Al.sub.0.3Ga.sub.0.7As is set to .lamda./4n (where n is a
refractive index of each semiconductor layer). The selective
oxidation layer 107 is constituted by p-AlAs and formed in the
reflection layer 106.
[0107] More specifically, the selective oxidation layer 107 is
formed in the position of 7.lamda./4 from the resonator spacer
layer 105. And the selective oxidation layer 107 includes
non-oxidizing region 107a and oxidization region 107b and has a
thickness of 20 nm.
[0108] The contact layer 108 is constituted by p-GaAs and formed on
the reflection layer 106.
[0109] The SiO.sub.2 layer 109 is formed to cover one principal
plane of the part of resonator spacer layer 103 and the end faces
of the active layer 104, the resonator spacer layer 105, the
reflection layer 106, the selective oxidation layer 107, and the
contact layer 108.
[0110] The insulating resin 110 is formed in contact with the
SiO.sub.2 layer 109. The p-type electrode 111 is formed on the part
of contact layer 108 and the insulating resin 110. The n-type
electrode 112 is formed on the back of the substrate 101.
[0111] Each of the reflection layer 102,106 constitutes the
semiconductor distributed Bragg reflector which reflects the
emission light emitted from the active layer 104 through Bragg's
multipath reflection and includes the emission light in the active
layer 104.
[0112] The oxidization region 107b has a refractive index which is
smaller than that of the non-oxidizing region 107a. And the
oxidization region 107b confines in non-oxidizing region 107a the
emission light oscillated by active layer 104 while the current
poured in from p-type electrode 111 constitutes the current
narrowed area which restricts the course which flows into active
layer 104 to non-oxidizing region 107a.
[0113] In this manner, the emission of the surface-emitting laser
element 1 with a low threshold current is attained. Thus, the
current narrowing area is produced by performing selective
oxidation of the oxidization region 107b of selective oxidation
layer 107. Therefore, the current narrowing area is a selective
oxidation type.
[0114] FIG. 3 is a cross-sectional view showing the neighborhood of
the active layer 104 of the surface-emitting laser element 1 of
FIG. 2. As shown in FIG. 3, the reflection layer 102 includes low
refractive index layer 1021, high refractive index layer 1022, and
composition inclination layer 1023.
[0115] The low refractive index layer 1021 is constituted by
n-AlAs, and the high refractive index layer 1022 is constituted by
n-Al.sub.0.3Ga.sub.0.7As.
[0116] The composition inclination layer 1023 is constituted by
n-AlGaAs in which the content of Al changes gradually toward
another side from the low refractive index layer 1021 or the high
refractive index layer 1022.
[0117] And the low refractive index layer 1021 touches the
resonator spacer layer 103. The reflective layer 106 includes low
refractive index layer 1061, high refractive index layer 1062, and
composition inclination layer 1063.
[0118] The low refractive index layer 1061 is constituted by
p-Al.sub.0.9Ga.sub.0.1As, and the high refractive index layer 1062
is constituted by p-Al.sub.0.3Ga.sub.0.7As. The composition
inclination layer 1063 is constituted by p-AlGaAs in which the
content of Al changes gradually toward another side from the low
refractive index layer 1061 or the high refractive index layer
1062.
[0119] And the low refractive index layer 1061 touches the
resonator spacer layer 105. The active layer 104 is constituted by
the quantum well structure where three well layers 1041 each of
which is constituted by GaInPAs, and four barrier layers 1042 each
of which is constituted by Ga.sub.0.6In.sub.0.4P are laminated
alternately.
[0120] And the barrier layer 1042 touches the resonator spacer
layer 103,105. GaInPAs which constitutes the well layer 1041 has a
compressive strain, and Ga.sub.0.6In.sub.0.4P which constitutes the
barrier layer 1042 has a tensile strain.
[0121] In the surface-emitting laser element 1, the resonator
spacer layer 103,105 and the active layer 104 constitute a
resonator, and the thickness of the resonator in a direction
perpendicular to the substrate 101 is set to one wavelength
(=.lamda.) of the surface-emitting laser element 1. That is, the
resonator spacer layer 103,105 and the active layer 104 constitute
a one-wave resonator.
[0122] Each of the surface-emitting laser elements 2-32 shown in
FIG. 1 is constituted to have the composition which is the same as
the composition of the surface-emitting laser element 1 of FIG. 2
and FIG. 3.
[0123] FIGS. 4A-4C, FIGS. 5A-5C, and FIGS. 6A and 6B are diagrams
for explaining the method of manufacturing the surface-emitting
laser array 100 of FIG. 1. In FIGS. 4A-6B, the manufacturing
process in the case of producing four surface-emitting laser
elements 1, 9, 17, and 25 among 32 surface-emitting laser elements
1-32 in the surface-emitting laser array 100 of FIG. 1 will be
explained as an example of the method of manufacturing the
surface-emitting laser array 100.
[0124] In FIG. 4A, upon start of this manufacturing process, the
metal-organic chemical vapor deposition (MOCVD) process is
performed. Reflective layer 102, resonator spacer layer 103, active
layer 104, resonator spacer layer 105, reflection layer 106,
selective oxidation layer 107, and contact layer 108 are laminated
one by one on substrate 101 (refer to FIG. 4A).
[0125] In this case, n-AlAs and n-Al.sub.0.3Ga.sub.0.7As of the
reflection layer 102 are formed by using trimethyl aluminum (TMA),
trimethyl gallium (TMG), arsine (AsH3), and hydrogen selenide
(H.sub.2Se) as source materials.
(Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P of the resonator spacer
layer 103 is formed by using trimethyl aluminum (TMA), trimethyl
gallium (TMG), trimethyl indium (TMI), and phosphine (PH.sub.3) as
source materials.
[0126] And GaInPAs of the active layer 104 is formed by using
trimethyl gallium (TMG), trimethyl indium (TMI), phosphine
(PH.sub.3), and arsine (AsH3) as source materials.
Ga.sub.0.6In.sub.0.4P of the active layer 104 is formed by using
trimethyl gallium (TMG), trimethyl indium (TMI), and phosphine
(PH3) as source materials.
[0127] And (Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P of the
resonator spacer layer 105 is formed by using trimethyl aluminum
(TMA), trimethyl gallium (TMG), trimethyl indium (TMI), and
phosphine (PH3) as source materials.
p-Al.sub.0.9Ga.sub.0.1As/p-Al.sub.0.3Ga.sub.0.7As of the reflection
layer 106 is formed by using trimethyl aluminum (TMA), trimethyl
gallium (TMG), arsine (AsH3), and carbon tetrabromide (CBr.sub.4)
as source materials. Instead of carbon tetrabromide (CBr.sub.4),
dimethyl zinc (DMZn) may be used.
[0128] And p-AlAs of the selective oxidation layer 107 is formed by
using trimethyl aluminum (TMA), arsine (AsH.sub.3) and carbon
tetrabromide (CBr.sub.4) as source materials. p-GaAs of the contact
layer 108 is formed by using trimethyl gallium (TMG), arsine
(AsH.sub.3) and carbon tetrabromide (CBr.sub.4) as source
materials. Also in this case, instead of carbon tetrabromide
(CBr.sub.4), dimethyl zinc (DMZn) may be used.
[0129] Then, resist is applied to the contact layer 108 and a
resist pattern 120 is formed on the contact layer 108 using
photoengraving process technology (refer to FIG. 4B).
[0130] If the resist pattern 120 is formed, the formed resist
pattern 120 is used as a mask. Dry etching of the part of the
resonator spacer layer 103, the active layer 104, the resonator
spacer layer 105, the reflection layer 106, the selective oxidation
layer 107, and the contact layer 108 is carried out, and the resist
pattern 120 is removed further.
[0131] In this case, the part of resonator spacer layer 103, the
active layer 104, the resonator spacer layer 105, the reflection
layer 106, the selective oxidation layer 107, and the contact layer
108 are subjected to a halogen base gas of Cl.sub.2, BCl.sub.3,
SiCl.sub.4, CCl.sub.4, or CF.sub.4 introduced thereto. Etching is
performed by using the dry etching method using plasma, such as the
reactive ion beam etching (RIBE) method, the
inductively-coupled-plasma (ICP) etching method, and the reactive
ion etching (RIE) method.
[0132] And during etching of the part of resonator spacer layer
103, the active layer 104, the resonator spacer layer 105, the
reflection layer 106, the selective oxidation layer 107, and the
contact layer 108, a plasma emission spectrum analysis is performed
from the window of the etching system, and a time change with the
emission intensity of 451 nm of In is monitored.
[0133] Since emission of 1n can be detected only when the region of
the resonator is etched, etching can be easily stopped in the
resonator region which is constituted by a AlGaInPAs base
material.
[0134] As a result, mesa structures 131-134 in the surface-emitting
laser elements 1, 9, 17, and 25 are formed (refer to FIG. 4C).
[0135] Each of the mesa structures 131-134 is constituted by the
part of resonator spacer layer 103, the active layer 104, the
resonator spacer layer 105, the reflection layer 106, the selective
oxidation layer 107, and the contact layer 108.
[0136] Alternatively, the part of resonator spacer layer 103, the
active layer 104, the resonator spacer layer 105, the reflection
layer 106, the selective oxidation layer 107, and the contact layer
108 may be etched by wet etching.
[0137] When selective etching of the reflection layer 106, the
selective oxidation layer 107, and the contact layer 108, which are
constituted by a AlGaAs material, is performed by wet etching, a
sulfuric-acid base etchant may be used.
[0138] Next, as shown in FIGS. 5A-5C, after the process of FIG. 4C
is completed, in the atmosphere in which bubbling of water heated
at 85 degrees C. is performed with nitrogen gas, a sample is heated
at 350 degrees C. and the circumference of the selective oxidation
layer 107 is oxidized in the direction from the peripheral part to
the central part, so that non-oxidizing region 107a and oxidization
region 107b are formed in the selective oxidation layer 107 (refer
to FIG. 5A).
[0139] Then, the SiO.sub.2 layer 109 is formed all over the sample
using the chemical vapor depositing (CVD) method, and the region
which serves as a light emitting part and the SiO.sub.2 layer 109
in its adjacent areas are removed using the electrophotographic
process (refer to FIG. 5B).
[0140] Next, the insulating resin 110 is applied to the whole
sample by the spin coat, and the insulating resin 110 in the region
used as the light emitting part is removed (FIG. 5C).
[0141] Next, as shown in FIG. 6A and FIG. 6B, after the insulating
resin 110 is formed, the resist pattern which has a predetermined
size is formed in the region used as the light emitting part, a
p-type electrode material is formed all over the sample by the
vapor deposition method, the p-type electrode material on the
resist pattern is removed by the lift-off method, and the p-type
electrode 111 is formed (refer to FIG. 6A).
[0142] And the back of the substrate 101 is ground, a n-type
electrode 112 is formed on the back of the substrate 101 and
further annealed to create the ohmic conduction of the p-type
electrode 111 and the n-type electrode 112 (refer to FIG. 6B). In
this manner, the surface-emitting laser array 100 is produced.
[0143] In the processes of FIG. 4B and FIG. 4C, the dry etching for
forming the four surface-emitting laser elements is illustrated.
However, in practice, the dry etching for forming 32
surface-emitting laser elements 1-32 of FIG. 1 simultaneously is
performed in the processes of FIG. 4B and FIG. 4C.
[0144] In this case, the resist pattern for forming simultaneously
32 surface-emitting laser elements 1-32 is formed using the
photomask which is in conformity with the arrangement of 32
surface-emitting laser elements 1-32 of FIG. 1. Namely, the resist
pattern for forming simultaneously 32 surface-emitting laser
elements 1-32 is arranged so that the intervals X and d are set up
to meet the condition d<X, and eight normals to straight lines
arranged in the sub-scanning direction from the eight centers of
the eight surface-emitting laser elements 1-8/9-16/17-24/25-32
arrayed in the main scanning direction are arranged at equal
intervals of c1.
[0145] In the surface-emitting laser array 100, the interval d of
the surface-emitting laser elements arranged in the sub-scanning
direction is set up to be smaller than the interval X of the
surface-emitting laser elements arranged in the main scanning
direction. Thereby, when compared to the case where the interval d
is made larger than the interval X, the interval c1 (=d/8) can be
made small and this is advantageous to high density recording.
[0146] It is also possible to narrow both the interval of the
surface-emitting laser elements arranged in the sub-scanning
direction and the interval of the surface-emitting laser elements
arranged in the main scanning direction. However, it is necessary
to extend at least one interval in order to secure a space required
for wiring of the elements and reduction of the influence of the
thermal interference between the elements. Thus, in order to
perform high-density writing, it is preferred to extend the
interval in the main scanning direction.
[0147] FIG. 7 is a diagram for explaining etching in the process of
FIG. 4B. FIG. 7 shows a distribution of etching depth in an
in-surface direction DR1 of the substrate 101 when etching of the
crystal layer constituted by any of the resonator spacer layer 103,
the active layer 104, the resonator spacer layer 105, the
reflection layer 106, the selective oxidation layer 107, and the
contact layer 108 is performed without using the resist pattern
120.
[0148] As shown in FIG. 7, a distribution of etching depth in the
in-surface direction DR1 of the substrate 101 when etching of the
contact layer 108, the selective oxidation layer 107, and the
reflection layer 106 (called region REG1) is represented by the
curve k1. On the other hand, a distribution of etching depth in the
in-surface direction DR1 of the substrate 101 when etching of the
resonator spacer layer 105, the active layer 104, and the resonator
spacer layer 103 (called region REG2) is represented by the curve
k2.
[0149] Since the reflection layer 106, the selective oxidation
layer 107, and the contact layer 108 are constituted by an AlGaAs
base material as mentioned above, the etching rate is relatively
large and the distribution of etching depth of the region REG1 in
the in-surface direction DR1 is relatively large (see the curve
k1).
[0150] On the other hand, since the resonator spacer layer 103,105
and the active layer 104 contain In and the vapor pressure of the
reactant of 1n is low, the etching rate of the resonator spacer
layer 103,105 and the active layer 104 is smaller than the etching
rate of the reflection layer 106, the selective oxidation layer
107, and the contact layer 108. Thus, the distribution of etching
depth of the region REG2 in the in-surface direction DR1 is smaller
than the distribution of in-surface direction DR1 of etching depth
of the region REG1 (see the curve k2).
[0151] Namely, a difference of etching depth produced in the region
REG1 in the in-surface direction DR1 is absorbed by lowering of the
etching rate in the region REG2. As a result, the distribution of
etching depth of the region REG2 in the in-surface direction DR1 is
smaller than the distribution of etching depth of the region REG1
in the in-surface direction DR1.
[0152] Next, an experimental result which shows that the etching
rate of the region REG2 containing In is smaller than the etching
rate of the region REG1 constituted by an AlGaAs base material will
be explained.
[0153] FIG. 8 and FIG. 9 are first and second timing charts for
explaining the plasma emission at the time of etching when
producing the surface-emitting laser array 100 of FIG. 1,
respectively.
[0154] In FIG. 8 and FIG. 9, the vertical axis expresses the
intensity of plasma emission light and the horizontal axis
expresses the time. FIG. 8 shows the case where etching is
performed to the middle of the resonator region, and FIG. 9 shows
the case where etching is performed from the resonator region to
the third cycle one of the reflection layer 102.
[0155] In FIG. 8, the curve k3 shows the emission intensity of
gallium (Ga), the curve k4 shows the emission intensity of indium
(In), and the curve k5 shows the emission intensity of aluminum
(aluminum).
[0156] In FIG. 9, the curve k6 shows the emission intensity of Ga,
the curve k7 shows the emission intensity of 1n, and the curve k8
shows the emission intensity of aluminum.
[0157] In the experiment, a sample in which the thickness from the
surface to the interface between the reflection layer 106 and the
resonator region is 3.18 micrometers, and the thickness of the
resonator region containing In is 0.23 micrometer is used.
[0158] The etching rate in the region from the surface to the
interface between the reflection layer 106 and the resonator region
is 3.18 micrometers/871 seconds=3.65.times.10.sup.-3
micrometers/sec. On the other hand, the etching rate in the
resonator region is 0.23 micrometers/372
seconds=6.18.times.10.sup.-4 micrometers/sec (refer to FIG. 9).
[0159] As described above, in the resonator region containing In,
the etching rate falls. Although the thickness (=0.23 micrometers)
of the resonator region is smaller than the thickness (=3.18
micrometers) of the region above the resonator region, the
resonator region requires a longer time for etching.
[0160] The emission intensity of 1n increases in the resonator
region (see the curves k4 and k7). Therefore, etching can be easily
stopped in the resonator region by detecting an increase of the
emission intensity of In.
[0161] The emission intensity of Ga and the emission intensity of
Al changes periodically with progress of the etching time, and the
amplitude of the emission intensity decreases gradually with
progress of the etching time (see the curves k3, k5, k6, and
k8).
[0162] If the distribution of etching depth of the wafer in the
in-surface direction DR1 is uniform, the emission intensity of Ga
and the emission intensity of aluminum change periodically with a
constant amplitude.
[0163] On the other hand, if the distribution of etching depth of
the wafer in the in-surface direction DR1 is not uniform, the
emission of Al and the emission of Ga are observed simultaneously
so that the amplitude of the emission intensity of Ga and the
amplitude of the emission intensity of Al become small.
[0164] Therefore, the gradual decrease of the amplitude of the
emission intensity of Ga and the amplitude of the emission
intensity of Al with progress of the etching time means that a
difference of the etching depth arises in the in-surface direction
DR1 of the wafer with progress of the etching time.
[0165] And after etching is performed through the resonator region,
the amplitude of the emission intensity of Ga and the amplitude of
the emission intensity of Al decrease further. When the etching
bottom reaches the reflection layer 102, a larger difference of the
etching depth in the in-surface direction DR1 arises (see the
curves k6 and k8).
[0166] FIG. 10 is a diagram for explaining an etching depth in the
flat part at the time of stopping etching in the resonator region
and a difference between an etching depth in the inter-element gap
of the surface-emitting laser elements and an etching depth in the
flat part with respect to a mesa interval.
[0167] FIG. 11 is a diagram for explaining an etching depth in the
flat part at the time of stopping etching in the reflection layer
102 arranged on the substrate 101 side and a difference between an
etching depth in the inter-element gap of the surface-emitting
laser elements and an etching depth in the flat part with respect
to a mesa interval.
[0168] In FIG. 10 and FIG. 11, the vertical axis expresses the
difference .DELTA.d between the etching depth in the inter-element
gap and the etching depth in the flat part, and the horizontal axis
expresses the mesa interval.
[0169] In FIG. 10 and FIG. 11, .diamond-solid. denotes the flat
part etching depth and .diamond-solid. denotes the difference
.DELTA.d.
[0170] When etching is stopped in the middle of the resonator
region, even if the mesa interval is 10 micrometers or less, the
difference .DELTA.d between the etching depth in the inter-element
gap and the etching depth in the flat part is 100 nm or less (refer
to FIG. 10).
[0171] On the other hand, when etching is stopped in the reflection
layer 102 arranged on the substrate 101 side and the mesa interval
is about 23 micrometers, the difference .DELTA.d is set to 100 nm.
When the mesa interval is set to 20 micrometers or less, the
difference .DELTA.d exceeds 100 nm. And when the mesa interval is
10 micrometers or less, the difference .DELTA.d becomes large to
about 250 nm (refer to FIG. 11).
[0172] In this manner, even if a large difference in etching depth
between the inter-element part and the flat part arises by the time
the etching bottom reaches the resonator region, etching is stopped
in the resonator region containing In, the large difference in
etching depth is absorbed in the resonator region where the etching
rate is small. Even if the mesa interval becomes small, the
difference .DELTA.d in etching depth between the inter-element gap
and the flat part can be made small.
[0173] That is, since etching is stopped in the resonator region
containing In, it is possible to equalize the etching depth in the
in-surface direction DR1 of the wafer in which the inter-element
gap where the surface-emitting laser elements 1-32 are arranged
densely and the flat part where the surface-emitting laser element
is not formed co-exist.
[0174] FIG. 12 is a plan view and cross-sectional view of the
surface-emitting laser array 100 of FIG. 1. As shown in FIG. 12,
the region where the surface-emitting laser elements 1-32 are
arranged is the non-etching region, and the circumference of the
surface-emitting laser elements 1-32 is the etching region.
[0175] The cross-section taken along the line A-A' include the
cross-section of the surface-emitting laser elements 25-27 and the
flat part in the vicinity of the surface-emitting laser element 25.
The etching depth between the surface-emitting laser elements 25
and 26 and between the surface-emitting laser elements 26 and 27 is
set to D1, and the etching depth in the flat part in the vicinity
of the surface-emitting laser element 25 is set to D2.
[0176] And the etching depth D1 is smaller than the etching depth
D2. As a result, the difference between the etching depth D1 and
the etching depth D2 is set to .DELTA.d.
[0177] The skirt portions 141-145 are formed by etching the contact
layer 108, the selective oxidation layer 107, the reflection layer
106, the resonator spacer layer 105, the active layer 104, and the
resonator spacer layer 103. As mentioned above, the resonator
spacer layer 103,105 and the active layer 104 contain In and the
etching rate is relatively slow. For this reason, etching of the
surface-emitting laser array 100 in the in-surface direction DR1
also progresses at the time of etching of the resonator spacer
layer 103,105 and the active layer 104. As a result, the size of
the skirt portions 141-145 is smaller than that in the existing
surface-emitting laser array.
[0178] When the skirt portion in the etching configuration has an
inclination different from that of the side of the upper part of
the mesa structure and the oxidization narrowing layer is contained
in the skirt portion in the etching configuration, the width of the
selective oxidation layer is larger than the width of the upper
part of the mesa structure and it is difficult to estimate the
width of the selective oxidation layer correctly. As a result, the
estimate of the width of the oxidization region 107b becomes
inaccurate, and it is difficult to control the diameter of
oxidization narrowing correctly. Therefore, it is desired that the
etching bottom enters the resonator region through the whole array
chip.
[0179] When the thickness of the resonator region is equal to
.lamda. (the thickness of the one-wave resonator), it is desired to
perform etching so that the center in the thickness direction of
the resonator region is in conformity with the etching bottom (the
flat part), in order to attain uniformity of the etching depth in
the in-surface direction of the wafer surface. In this case, it is
desired that .DELTA.d is set to .lamda./2 or less as effectual
length in the medium.
[0180] Since the emission wavelength of each of the
surface-emitting laser elements 1-32 in this embodiment is 780 nm,
the thickness of a one-wave resonator is about 230 nm. Therefore,
it is desired that the difference .DELTA.d is equal to 115 nm or
less.
[0181] In the existing surface-emitting laser array, when the
difference .DELTA.d is 115 nm, the mesa interval is 20 micrometers
or less (refer to FIG. 11). In the surface-emitting laser array 100
of the invention, the difference .DELTA.d is smaller than 100 nm
even if the mesa interval is about 20 micrometers. Therefore, the
invention is effective when the mesa interval is below 20
micrometers. The thickness of an one-wave resonator is smaller if
the wavelength is shorter than 780 nm, and the difference .DELTA.d
exceeds .lamda./2 in the region where the mesa interval is
larger.
[0182] As mentioned above, in the surface-emitting laser array 100,
mesa etching for forming the mesa structure is stopped in the
middle of the resonator region containing In (or in the middle of
the resonator spacer layer 103). Even if the mesa interval becomes
small, the difference .DELTA.d in etching depth between the
inter-element gap and the flat part becomes small, and the low
refractive index layer (=AlAs) of the reflection layer 102 is not
exposed in the flat part. As a result, even if the selective
oxidation of the selective oxidation layer 107 is performed, the
low refractive index layer (=AlAs) of the reflection layer 102 is
not oxidized.
[0183] Therefore, according to the invention, it is possible to
escape the heat generated in the active layer 104 to the substrate
1 through AlAs (low refractive index layer) of the reflection layer
102, and it is possible to prevent accumulating heat in the active
layer 104 without using dummy elements.
[0184] The interval between two adjacent surface-emitting laser
elements in the inter-element part means a narrower one of the gap
between the surface-emitting laser elements in the position of the
top surface of the mesa structure and the gap between the
surface-emitting laser elements in the position of the bottom
surface of the mesa structure. Whether the gap between the
surface-emitting laser elements in the position of the top surface
of the mesa structure is larger or the gap between the
surface-emitting laser elements in the position of the bottom
surface of the mesa structure is larger depends on the method of
etching for forming the mesa structure.
[0185] FIG. 13 is a plan view of a surface-emitting laser array in
an embodiment of the invention. As shown in FIG. 13, the
surface-emitting laser array 100A is essentially the same as the
surface-emitting laser array 100 of FIG. 1 except that
surface-emitting laser elements 33-40, pads 83-90, and wires
W33-W40 are added to the surface-emitting laser array 100 of FIG.
1.
[0186] In the surface-emitting laser array 100A, the
surface-emitting laser elements 1-40 are arranged in a
two-dimensional formation of four rows and ten columns. Each of the
surface-emitting laser elements 33-40 has the rectangle form one
side of which is 16 micrometers long, similar to that in each of
the surface-emitting laser elements 1-32.
[0187] And the four surface-emitting laser elements: 1, 11, 21,
31/2, 12, 22, 32/3, 13, 23, 33/4, 14, 24, 34/5, 15, 25, 35/6, 16,
26, 36/7, 17, 27, 37/8, 18, 28, 38/9, 19, 29, 39/10, 20, 30, 40 are
arranged in the sub-scanning direction while the ten
surface-emitting laser elements 1-10/11-20/21-30/31-40 are arranged
in the main scanning direction.
[0188] The rows of the ten surface-emitting laser elements
1-10/11-20/21-30/31-40 arranged in the main scanning direction are
shifted in a step-wise manner in the sub-scanning direction, and
they are arranged so that 40 laser beams emitted from the 40
surface-emitting laser elements 1-40 do not overlap mutually.
[0189] In the ten surface-emitting laser elements
1-10/11-20/21-30/31-40 arranged in the main scanning direction, the
gap between two adjoining surface-emitting laser elements is set to
an interval "X". In the four surface-emitting laser elements 1, 11,
21, 31/2, 12, 22, 32/3, 13, 23, 33/4, 14, 24, 34/5, 15, 25, 35/6,
16, 26, 36/7, 17, 27, 37/8, 18, 28, 38/9, 19, 29, 39/10, 20, 30, 40
arranged in the sub-scanning direction, the gap between two
adjoining surface-emitting laser elements is set to an interval
"d".
[0190] The ten normals from the respective centers of the ten
surface-emitting laser elements (e.g., the elements 31-40) arranged
in the main scanning direction, to the straight line parallel to
the sub-scanning direction are arranged at equal intervals of "c2"
in the sub-scanning direction to meet the condition "c2"="d"/10.
When the interval d is set to 24 micrometers, the interval c2 is
equal to 24/10=2.4 micrometers.
[0191] The ten normals from the respective centers of other ten
surface-emitting laser elements 1-10/11-20/21-30 arranged in the
main scanning direction, to the straight line parallel to the
sub-scanning direction are also arranged at equal intervals of "c2"
which is the same as mentioned above.
[0192] The pads 51-90 are arranged around the circumference of the
surface-emitting laser elements 1-40 arranged in two-dimensional
formation. The wires W1-W40 are arranged to connect the
surface-emitting laser elements 1-40 to the pads 51-90,
respectively. And each of the wires W33-W40 has a line width of 8
micrometers, for example.
[0193] The wires W1-W11, W20, W21, W30-W40 which connect the
surface-emitting laser elements 1-11, 20, 21, 30-40 arranged at the
outermost circumference among the surface-emitting laser elements
1-40 arranged in two-dimensional formation, to the pads 51-61, 70,
71, 80-90 respectively are arranged without passing by the two
adjoining surface-emitting laser elements.
[0194] The wires W12-W19, W22-W29 which connect the
surface-emitting laser elements 12-19, 22-29 arranged the inside
position among the surface-emitting laser elements 1-40 arranged in
two-dimensional formation, to the pads 62-69, 72-79 respectively
are arranged by passing by two adjoining surface-emitting laser
elements in the main scanning direction. If the line width of each
of the wires W1-W40 is 8 micrometers as mentioned above, each of
the wires W12-W19, W22-W29 can be arranged between two adjoining
surface-emitting laser elements in the main scanning direction.
[0195] In the region where the pads 51-90 are arranged, the
epitaxial layer remains, a groove 150 is formed around the
circumference of the surface-emitting laser elements 1-40, and the
groove 150 is embedded with polyimide. And the wires are arranged
to pass by the top of the polyimide layer. The pads 51-90 are
bonded to the epitaxial layer via the insulating layer. By this
formation (rather than forming of the pads 1-40 on polyimide), the
adhesion of the pads 1-40 and the insulating layer can be increased
and separation of the pads at the time of wire bonding can be
certainly prevented.
[0196] Each of the surface-emitting laser elements 33-40 has the
cross-sectional structure that is the same as that of the
surface-emitting laser element 1 of FIG. 2 and FIG. 3.
[0197] Therefore, mesa etching for forming the mesa structure in
the surface-emitting laser array 100A is stopped in the middle of
the resonator region containing In (the resonator spacer layer
103), and even if the mesa interval becomes small, the difference
.DELTA.d in etching depth between the inter-element gap and the
flat part becomes small, and the low refractive index layer (=AlAs)
of the reflection layer 102 is not exposed in the flat part. As a
result, even if the selective oxidation of the selective oxidation
layer 107 is performed, the low refractive index layer (=AlAs) of
the reflection layer 102 is not oxidized.
[0198] Therefore, according to this embodiment, the heat generated
in the active layer 104 can be escaped to the substrate 1 via AlAs
(low refractive index layer) of the reflection layer 102, and it is
possible to prevent the heat from being accumulated in the active
layer 104 without using dummy elements.
[0199] FIG. 14 is a plan view of a surface-emitting laser array in
an embodiment of the invention. As shown in FIG. 14, in the
surface-emitting laser array 200 of this embodiment, the
surface-emitting laser elements 1-32 of the surface-emitting laser
array 100 of FIG. 1 are replaced by surface-emitting laser elements
151-182, and the other composition is the same as that of the
surface-emitting laser array 100.
[0200] In the surface-emitting laser array 200, wires W1-W32
connect surface-emitting laser elements 151-182 to pads 51-82,
respectively. The surface-emitting laser elements 151-182 are
arranged in a two-dimensional formation of four rows and eight
columns.
[0201] Each of the surface-emitting laser elements 151-182 has a
rectangular form whose one side is equal to 16 micrometers. Eight
columns of four surface-emitting laser elements: 151, 159, 167,
175/152, 160, 168, 176/153, 161, 169, 177/154, 162, 170, 178/155,
163, 171, 179/156, 164, 172, 180/157, 165, 173, 181/158, 166, 174,
182 arranged in the sub-scanning direction, and eight
surface-emitting laser elements: 151-158/159-166/167-174/175-182
are arranged in the main scanning direction. Eight surface-emitting
laser elements: 151-158/159-166/167-174/175-182 arranged in the
main scanning direction are shifted in a step-wise manner in the
sub-scanning direction, and are arranged in it. As a result, 32
laser beams emitted from 32 surface-emitting laser elements 1-32 do
not overlap mutually.
[0202] In the eight surface-emitting laser elements:
151-158/159-166/167-174/175-182 arranged in the main scanning
direction, the gap between two adjoining surface-emitting laser
elements is set to the interval X.
[0203] In the four surface-emitting laser elements: 151, 159, 167,
175/152, 160, 168, 176/153, 161, 169, 177/154, 162, 170, 178/155,
163, 171, 179/156, 164, 172, 180/157, 165, 173, 181/158, 166, 174,
182 arranged in the sub-scanning direction, the gap between two
adjoining surface-emitting laser elements is set to the interval d.
The gaps in the sub-scanning direction of eight normals taken down
from eight centers of eight surface-emitting laser elements 151-158
arranged in the main scanning direction to the straight line
arranged in the sub-scanning direction are arranged at equal
intervals of c1.
[0204] The gaps in the sub-scanning direction between eight normals
to the straight lines from eight centers of eight surface-emitting
laser elements 159-166/167-174/175-182 arranged in the main
scanning direction arranged in the sub-scanning direction are also
arranged at equal intervals of c1.
[0205] FIG. 15 is a cross-sectional view of a surface-emitting
laser element 151 in the surface-emitting laser array of FIG. 14.
As shown in FIG. 15, in the surface-emitting laser element 151, the
resonator spacer layer 103,105 and the reflection layer 106 of the
surface-emitting laser element 1 shown in FIG. 2 are replaced by
resonator spacer layers 103A and 105A and a reflection layer 106A,
respectively, and the other composition is the same as that of the
surface-emitting laser element 1.
[0206] The resonator spacer layer 103A is constituted by non-doped
(Al.sub.0.1Ga.sub.0.9).sub.0.5In.sub.0.5P and formed on the
reflection layer 102. The resonator spacer layer 105A is
constituted by non-doped (Al.sub.0.1Ga.sub.0.9).sub.0.5In.sub.0.5P
and formed on the active layer 104.
[0207] The reflective layer 106A is constituted by
p-(Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P to form the low
refractive index layer nearest to the active layer 104 among the
reflection layers 106 shown in FIG. 2, and this reflection layer
106A is formed on the resonator spacer layer 105A.
[0208] And the reflection layer 106A constitutes a semiconductor
distribution Bragg reflector which reflects an emission light beam
emitted by the active layer 104 through Bragg's multipath
reflection and includes the light beam in the active layer 104.
[0209] FIG. 16 is a cross-sectional view showing the neighborhood
of the active layer 104 of the surface-emitting laser element 151
shown in FIG. 15. As shown in FIG. 16, the low refractive index
layer 1021 of reflection layer 102 touches the resonator spacer
layer 103A. The resonator spacer layer 103A touches the low
refractive index layer 1021 of reflection layer 102 and the barrier
layer 1042 of active layer 104. In the reflective layer 106A, the
low refractive index layer 1061 nearest to the active layer 104
among the reflection layers 106 shown in FIG. 3 is replaced by the
low refractive index layer 1061A, and the other composition is the
same as that of the reflection layer 106.
[0210] And the low refractive index layer 1061A is constituted by
p-(Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P and touches the
resonator spacer layer 105A. The resonator spacer layer 105A
touches the barrier layer 1042 of active layer 104 and the low
refractive index layer 1061A of reflection layer 106A.
[0211] In the surface-emitting laser element 151, the resonator
spacer layers 103A and 105A and the active layer 104 constitute a
resonator, and the thickness of the resonator in a direction
perpendicular to the substrate 101 is set to one wavelength
(=.lamda.) of the surface-emitting laser element 151. That is,
resonator spacer layers 103A and 105A and active layer 104
constitute an one-wave resonator.
[0212] Each of the surface-emitting laser elements 152-182 shown in
FIG. 14 has the composition which is the same as the composition of
the surface-emitting laser element 151 shown in FIGS. 15 and
16.
[0213] The surface-emitting laser array 200 is produced according
to the manufacturing process of FIGS. 4A-6B.
[0214] In this case, in the process of FIG. 4A,
(Al.sub.0.1Ga.sub.0.9).sub.0.5In.sub.0.5P of the resonator spacer
layers 103A and 105A is formed through the MOCVD method by using
trimethyl aluminum (TMA), trimethyl gallium (TMG), trimethyl indium
(TMI) and phosphine (PH3) as source materials. And
p-(Al0.7Ga0.3)0.5In0.5P which constitutes the low refractive index
layer 1061A of reflection layer 106A is formed through the MOCVD
method by using trimethyl aluminum (TMA), trimethyl gallium (TMG),
trimethyl indium (TMI), phosphine (PH3), and dimethyl zinc (DMZn)
as source materials. Instead of dimethyl zinc (DMZn), carbon
tetrabromide (CBr.sub.4) may be used.
[0215] In each of the surface-emitting laser elements 151-182 of
the surface-emitting laser array 200, the resonator (=resonator
spacer layers 103A and 105A and active layer 104) and the part of
reflection layer 106A (low refractive index layer 1061A) contains
In, and the thickness of the layer containing In is larger than
that in the surface-emitting laser elements 1-32. Therefore,
control of etching of the surface-emitting laser array 200 is made
easier when compared with that of the surface-emitting laser array
100.
[0216] In this embodiment, only the low refractive index layer
1061A nearest to the resonator among the reflection layers 106A
contains In. Alternatively, this embodiment may be modified so that
both a low refractive index layer and a high refractive index layer
of the upper reflection layer 106A of the resonator nearer to the
resonator contain In. In this case, the low refractive index layer
is constituted by (Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P, and
the high refractive index layer is constituted by
(Al.sub.0.1Ga.sub.0.9).sub.0.5In.sub.0.5P. In this case, two or
more layers may contain In, and the sum of thickness of the layers
containing In can be made larger.
[0217] And p-(Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P which is a
wide band gap is used in many cases by doping Zn or Mg. Such
dopants are easy to be spread. If they are spread to the active
layer 104, the active layer 104 may be damaged, which causes the
emission light efficiency to decline and causes the reliability to
fall.
[0218] In the surface-emitting laser elements 151-182,
p-(Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P is arranged in the
reflection layer 106A apart from the active layer 104 than the
resonator spacer layer 105A, and the resonator spacer layers 103A
and 105A are constituted by undoped
(Al.sub.0.1Ga.sub.0.9).sub.0.5In.sub.0.5P. It is possible to
prevent the undesired influence of impurities from arising.
[0219] Thus, mesa etching for forming mesa structure in the
surface-emitting laser array 200 is stopped in the middle of the
region containing In (or in the middle of the resonator spacer
layer 103A). Even if the mesa interval becomes small, the
difference .DELTA.d in etching depth between the inter-element gap
and the flat part becomes small, and the low refractive index layer
1021 (=AlAs) of reflection layer 102 is not exposed in the flat
part. As a result, even if the selective oxidation of the selective
oxidation layer 107 is performed, the low refractive index layer
1021 (=AlAs) of reflection layer 102 is not oxidized.
[0220] Therefore, according to this embodiment, the heat generated
in the active layer 104 can be escaped to the substrate 1 via AlAs
(low refractive index layer) of the reflection layer 102, and it is
possible to prevent the heat from being accumulated in the active
layer 104 without using dummy elements. Since the surface-emitting
laser array 200 is provided with surface-emitting laser elements
151-182 whose layer thickness containing In is thicker than
surface-emitting laser elements 1-32, it can be stopped with
controllability more sufficient than surface-emitting laser array
100 in the layer which includes the etching bottom for In.
[0221] Next, the output characteristic of the surface-emitting
laser array 200 of this embodiment will be explained.
[0222] FIG. 17 is a cross-sectional view of the surface-emitting
laser element in the embodiment of FIG. 14 used for the experiment.
FIG. 18 is a cross-sectional view of a surface-emitting laser
element in a comparative example used for the experiment.
[0223] In the embodiment of FIG. 17, the thickness of three cycles
of the low refractive index layer 1021 (=AlAs) near the active
layer 104 among the reflection layers 102 of the surface-emitting
laser element 151 is set to 3.lamda./4, and the other composition
is the same as that of the surface-emitting laser element 151.
[0224] In the comparative example of FIG. 18, the reflection layer
102 of surface-emitting laser element 151 is replaced by a
reflection layer which is constituted by 30.5 cycles of
n-Al.sub.0.3Ga.sub.0.7As/n-AlAs and 10 cycles of
n-Al.sub.0.3Ga.sub.0.7As/n-Al.sub.0.9Ga.sub.0.1As. And each of
n-Al.sub.0.3Ga.sub.0.7As, n-AlAs, and n-Al.sub.0.9Ga.sub.0.1As has
a thickness of .lamda./4.
[0225] FIG. 19 is a diagram for explaining the relationship between
the optical output and the current which shows an experimental
result. In FIG. 19, the vertical axis expresses the optical output
and the horizontal axis expresses the current.
[0226] The curve k9 shows the relationship between the optical
output and the current of the surface-emitting laser element of the
invention, and the curve k10 shows the relationship between the
optical output and the current of the surface-emitting laser
element of the comparative example. The experiment was conducted by
observing the continuous wave (CW) at 20 degrees C. from the
surface-emitting laser element having the light emitting part with
an area of 16 square micrometers.
[0227] As is apparent from the experimental result of FIG. 19, the
saturation value of the optical output of the surface-emitting
laser element by the invention shifts to the high-electric-current
value side rather than the saturation value of the optical output
of the surface-emitting laser element of the comparative example,
and high output is obtained.
[0228] In the surface-emitting laser element according the
invention, since the low refractive index layer 1021 of reflection
layer 102 on the side of substrate 101 is constituted by AlAs
having high thermal conductivity, it is because the heat
dissipation by the side of substrate 101 became good and the
temperature rise of the element at the time of element operation
was controlled.
[0229] Thus, by the use of AlAs with high thermal conductivity
constituting low refractive index layer 1021 of reflection layer
102 provided in substrate 101, and adopting the composition which
makes the heat generated in active layer 104 radiate heat to the
substrate 101, it was proved experimentally the output
characteristic of the surface-emitting laser element and that the
output characteristic of the surface-emitting laser array can be
improved if it lengthens.
[0230] The surface-emitting laser array of this embodiment may be
provided with 40 surface-emitting laser elements arranged in four
rows.times.ten columns like surface-emitting laser array 100A
(refer to FIG. 13).
[0231] The surface-emitting laser array of the invention may be
provided so that the resonator spacer layer 103,103A of the
surface-emitting laser elements 1-40, 151-182 includes
surface-emitting laser elements constituted by
Ga.sub.0.5In.sub.0.5P. The surface-emitting laser array of the
invention may be provided so that the resonator spacer layer
103,103A of the surface-emitting laser elements 1-40,151-182
includes surface-emitting laser elements constituted by
(Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P/Ga.sub.0.5In.sub.0.5P. In
this case, (Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P is arranged on
the active layer 104 side, and Ga.sub.0.5In.sub.0.5P is arranged on
the reflection layer 102 side.
[0232] While the carrier to the active layer 104 by
(Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P shuts up and is
increased, the heat generated in the active layer 104 can be made
to radiate heat to the reflection layer 102 more.
Ga.sub.0.5In.sub.0).sub.5P has a thermal conductivity higher than
(Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P.
[0233] Table 1 shows a difference in band gap between the resonator
spacer layer 103,105; 103A, 105A, and the well layer 1041 and a
difference in band gap between the barrier layer 1042 and the well
layer 1041 in the case where the well layers 1041 of the resonator
spacer layer 103,105; 103A,105A/the active layer 104 are formed
from AlGaAs/AlGaAs and in the case where the well layers 1041 are
formed from AlGaInP/GaInPAs, respectively.
TABLE-US-00001 TABLE 1 Wavelength 780 nm Spacer Layer
Al.sub.0.6Ga.sub.0.4As (Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P
(Eg = 2.0226 eV) (Eg = 2.324 eV) Active Layer Well Layer
Al.sub.0.12Ga.sub.0.88As GaInAs (Eg = 1.5567 eV) (Eg = 1.5567 eV)
Barrier Al.sub.0.3Ga.sub.0.7As Ga.sub.0.6In.sub.0.4P Layer (Eg =
1.78552 eV) (Eg = 2.02 eV) .DELTA.Eg (spacer/well) 465.9 meV 767.3
meV .DELTA.Eg (barrier/well) 228.8 meV 463.3 meV Wavelength 850 nm
(reference) Spacer Layer Al.sub.0.6Ga.sub.0.4As (Eg = 2.0226 eV)
Active Layer Well Layer GaAs (Eg = 1.42 eV) Barrier Layer
Al.sub.0.3Ga.sub.0.7As (Eg = 1.78552 eV) .DELTA.Eg (spacer/well)
602.6 eV .DELTA.Eg (barrier/well) 365.5 eV
[0234] When AlGaAs and AlGaAs are used for the resonator spacer
layer 103,105; 103A,105A and the well layer 1041 of the active
layer 104, respectively, the difference in band gap between the
resonator spacer layer 103,105; 103A,105A and the well layer 1041
in the surface-emitting laser element whose emission wavelength is
780 nm is 465.9 meV, and the difference in band gap between the
barrier layer 1042 and the well layer 1041 is 228.8 meV.
[0235] When AlGaAs and AlGaAs are used for the resonator spacer
layer 103,105; 103A,105A and the well layer 1041 of the active
layer 104, respectively, the difference in band gap between the
resonator spacer layer 103,105; 103A,105A and the well layer 1041
in the surface-emitting laser element whose emission wavelength is
850 nm is 602.6 meV, and the difference in band gap between the
barrier layer 1042 and the well layer 1041 is 365.5 meV.
[0236] On the other hand, when AlGaInP and GaInPAs are used for the
resonator spacer layer 103,105; 103A,105A and the well layer 1041
of the active layer 104, respectively, the difference in band gap
between the resonator spacer layer 103,105; 103A,105A and the well
layer 1041 in the surface-emitting laser elements 1-40,151-182
whose emission wavelength is 780 nm is 767.3 meV and the difference
in band gap between the barrier layer 1042 and the well layer 1041
is 463.3 meV.
[0237] Thus, by constituting the resonator spacer layer 103,105;
103A,105A and the well layer 1041 of the active layer 104 by
AlGaInP and GaInPAs, respectively, the difference in band gap
between the resonator spacer layer 103,105; 103A,105A and the well
layer 1041 and the difference in band gap between the barrier layer
1042 and the well layer 1041 can be increased from before.
[0238] As a result, the locked-in effect of the carrier to the well
layer 1041 remarkably improves and the surface-emitting laser
elements 1-40,151-182 can emit a higher-output emission light while
oscillating with a low threshold. Since the active layer 104
contains GaInPAs which has a compressive strain, the increase in
gain becomes large according to band separation with a heavy hole
and a light hole.
[0239] Thereby, it becomes high gain and a high output emission
light can be obtained with a low threshold. This effect is not
acquired with the surface-emitting laser element (780 nm or 850 nm)
produced by the AlGaAs system which has the almost same lattice
constant as a GaAs substrate.
[0240] With the improvement in the carrier inclusion and high gain
by the active layer 104 constituted by distorted quantum well
structure, the threshold current of the surface-emitting laser
elements 1-40,151-182 can be lowered, the reduction of the
reflection factor by reflection layer 106,106A on the side of
optical extraction are attained with high output emission.
[0241] Since the active layer 104 contains a material which does
not contain aluminum and is considering it as aluminum free active
region (the quantum well active layer and the adjoining layer),
when the inclusion of oxygen to these regions decreases, it can
control formation of a non-emitting re-coupling center, and can
attain long-life operation. This makes the optical writing unit or
the light source unit recyclable.
[0242] In the above embodiment, the low refractive index layer 1021
of the reflection layer 102 is constituted by AlAs. Alternatively,
the low refractive index layer 1021 of the reflection layer 102
arranged rather than the active layer 104 at the substrate 101 side
should just consist of a semiconductor material which has an
oxidation rate of selective oxidation layer 107, and an oxidation
rate more than equivalent. Since the selective oxidation layer 107
is generally constituted by Al.sub.xGa.sub.1-xAs (x>=0.9), the
low refractive index layer 1021 constituted by AlAs generally has
an oxidation rate equivalent to or larger than the oxidation rate
of the selective oxidation layer 107.
[0243] In the case of the layer containing aluminum, if the content
of aluminum differs, the oxidation rate of the layer with a larger
content of aluminum is larger, and if the content of aluminum is
the same, the oxidation rate of the layer with a larger thickness
is larger.
[0244] In the above embodiment, all the low refractive index layers
1021 of the reflection layer 102 are constituted by AlAs.
Alternatively, the reflection layer 102 should just equip the
active layer 104 side with the low refractive index layer
(=Al.sub.xGa.sub.1-xAs (x>=0.9)) which has an oxidation rate
more than the oxidation rate of selective oxidation layer 107. This
is because the effect which radiates heat to substrate 101 in the
heat generated in active layer 104 is high to make high the thermal
conductivity of the portion near a heating source (=active layer
104).
[0245] In the above embodiment, mesa etching is stopped in the
middle of the resonator spacer layer 103,103A. Alternatively, in
the surface-emitting laser array 100,100A, it is adequate that mesa
etching is stopped in the inside of the resonator (resonator spacer
layer 103, active layer 104, and resonator spacer layer 105) or at
the interface of the resonator and the reflection layer 106. In the
surface-emitting laser array 200, it is adequate that mesa etching
is stopped in the inside of the resonator (the resonator spacer
layer 103A, the active layer 104 and the resonator spacer layer
105A), or the inside of the low refractive index layer 1061A of the
reflection layer 106A, or at the interface of the low refractive
index layer 1061A and the high refractive index layer 1062.
Generally, it is adequate that mesa etching is stopped on the
reflection layer 106 side rather than the reflection layer 102.
[0246] FIG. 20 is a plan view of a surface-emitting laser array in
an embodiment of the invention. As shown in FIG. 20, the
surface-emitting laser array 300 of this embodiment includes
substrate 310, surface-emitting laser elements 311-320, and pads
321-330.
[0247] The surface-emitting laser elements 311-320 are arranged on
the substrate 310 in one dimensional formation. And the
surface-emitting laser elements 311-320 are constituted by the
surface-emitting laser elements 1-40 or the surface-emitting laser
elements 151-182 mentioned above.
[0248] The pads 321-330 are arranged around the surface-emitting
laser elements 311-320 and connected to the p-type electrode 111,
respectively. A threshold rise is controlled, and by accumulating
many field emission laser devices 311-320 in which high-output
operation is possible on the same substrate 310, since much data
transmission by a beam becomes simultaneously possible for example,
when it uses for optical communications, high-speed communication
can be performed.
[0249] Since the radiation characteristic of the heat generated in
active layer 104 is also good while operating with low power,
surface-emitting laser elements 311-320 can reduce a temperature
rise, when it captures into apparatus and uses especially.
[0250] Next, a description will be given of a method of
manufacturing the surface-emitting laser array in an embodiment of
the invention with reference to FIGS. 21A-23.
(1) Using the crystal growth using the metal-organic chemical vapor
deposition (MOCVD) method, semiconductor layers, including
reflection layer (lower reflector) 102, resonator spacer layer
(lower spacer layer) 103, active layer 104, resonator spacer layer
(upper spacer layer) 105, selective oxidation layer 107, and
reflection layer (upper reflector) 106, are laminated on the
substrate 101 one by one (refer to FIG. 21A). In the following, the
semiconductor layered product in which these layers are laminated
is called multilayer semiconductor film. (2) A pattern of photomask
PM corresponding to the light emitting part and the array boundary
part is formed on the surface of the multilayer semiconductor film
(which surface is opposite to the substrate 101) through the photo
lithography method (refer to FIG. 21B). In this example, one chip
has nine light emitting parts (3.times.3). (3) The shape of mesa is
formed through the dry etching method using the photomask PM as an
etching mask (refer to FIG. 21C). In the following, the shape of
mesa is called "mesa" for the sake of convenience. At this time,
etching is also performed in the portion used as the array boundary
part. In this example, etching is performed until the etching
bottom reaches the lower spacer layer 103. (4) The photomask PM is
removed. (5) The current narrowing structure is formed in the
selective oxidation layer 107 (refer to FIG. 21D). (6) A pattern of
etching mask for etching the array boundary part is formed through
the photolithography method. (7) Etching is performed for the array
boundary part until the etching bottom reaches the substrate 101
(refer to FIG. 22A). Each array part is separated or isolated from
other array parts, respectively. (8) A protection film 109 made of
any of SiO.sub.2, SiN and SiON is formed as a passivation film
(refer to FIG. 22B). (9) Etching is performed to remove the
passivation film at the divided part of the contact of the mesa
upper part and the bottom of the array boundary part (refer to FIG.
22C). At this time, the part of the passivation film on the side of
the array boundary part is masked so that it is not etched. (10)
The p-type electrode 111 is formed through the lift-off method
(refer to FIG. 22D). The portions other than the electrode are
masked beforehand by photoresist, and after vapor deposition of the
electrode material ultrasonic cleaning is performed in a solution,
such as acetone in which the photoresist dissolves. A multilayer
film of Cr/AuZn/Au or a multilayer film of Ti/Pt/Au is used as a
p-type electrode material. (11) After grinding of the back surface
of the substrate 101 is performed to reach a predetermined
thickness (about 100 micrometers), the n-type electrode 112 is
formed (refer to FIG. 23). The n-type electrode 112 is constituted
by a multilayer film of AuGe/Ni/Au. (12) The wiring for
establishing electrical connections between the electrode pads (not
shown) and the electrode pads corresponding to the respective
p-type electrodes 111 of the light emitting parts is formed. An
opening is formed in the center of the p-type electrode 111, and a
laser beam is emitted from this opening. Thereby, each mesa serves
as a light emitting part. (13) Cutting is performed along the
divided part of the bottom of the array boundary part to divide the
wafer into chips.
[0251] The thus produced surface-emitting laser array 400 of this
embodiment is shown in FIG. 24. Since this surface-emitting laser
array 400 is produced as a divided chip at the time of manufacture,
it is possible to reduce the curvature of the substrate 101.
Therefore, a manufacturing yield improves and it is possible to
attain low cost production.
[0252] Since the side of the lower reflector 102 in the
surface-emitting laser array 350 is covered by the protection film,
it is possible to suppress the low refractive index layer of the
lower reflector 102 reacting with moisture in the atmosphere to be
oxidized so that distortion is caused and destruction is caused to
advance. That is, degradation with the passage of time can be
prevented, and it is possible to realize formation of a reliable
surface-emitting laser array.
[Applications]
[0253] FIG. 25 is a diagram showing the composition of an optical
scanning device using the surface-emitting laser array 100A of FIG.
13.
[0254] As shown in FIG. 25, the optical scanning device 400
includes a light source 401, a coupling lens 402, an aperture 403,
an anamorphic lens 404, a polygon mirror 405, a deflector side
scanning lens 406, an image surface side scanning lens 407, a
dust-proof glass 408, an image surface glass 408, an image surface
409, a soundproof glass 410, and a dummy lens 411.
[0255] The light source 401 is constituted by the surface-emitting
laser array 100A shown in FIG. 13. 40 light beams emitted from the
light source 401 enter the coupling lens 402 and the coupling lens
402 converts them into slightly divergent light beams and guides
them to enter the anamorphic lens 404.
[0256] And the light beams incident to the anamorphic lens 404 are
converted by the anamorphic lens 404 so that they are parallel in
the main scanning direction and convergent in the sub-scanning
direction in the vicinity of the polygon mirror 405.
[0257] Then, the light beams enter the polygon mirror 405 through
the aperture 403, the dummy lens 411, and the soundproof glass
410.
[0258] And the light beams are deflected by the polygon mirror 405,
pass through the dust-proof glass 408, and image formation is
carried out on the image surface 409 by the deflector side scanning
lens 406 and the image surface side scanning lens 407.
[0259] The light source 401 and the coupling lens 402 are commonly
fixed to a component which is made of aluminum.
[0260] The light source 401 is constituted by the surface-emitting
laser array 100A including 40 surface-emitting laser elements 1-40
arranged so that the gaps in the sub-scanning direction of ten
normals to straight lines arranged in the sub-scanning direction
from ten centers of the ten surface-emitting laser element
1-10/11-20/21-30/31-40 are arranged at equal intervals of c2 by
adjusting the timing of lighting of 40 surface-emitting laser
elements 1-40, it can regard on the photoconductor as the same
composition as the case where the light source is located in a line
in the sub-scanning direction at equal intervals.
[0261] The gap of optical writing in the sub-scanning direction can
be adjusted by adjusting the inter-element gap c2 of the
surface-emitting laser elements 1-40, and the magnification of the
optical system. That is, when the surface-emitting laser array 100A
(40 channels) is used as light source 401, since the inter-element
gap c2 is set as 2.4 micrometers to have mentioned above, it can
perform the high-density writing of 4800 dpi by setting up the
magnification of the optical system about 2.2 times.
[0262] By increasing the number of the elements in the main
scanning direction, making smaller the interval c2 between the
adjoining surface-emitting elements arranged in the main-scanning
direction, making smaller the interval d between the
surface-emitting laser elements arranged in the sub-scanning
direction, or lowering the magnification of the optical system,
high-density optical writing may be attained with high quality
printing. In this case, the optical writing gap of the main
scanning direction is easily controllable by adjusting the lighting
timing of the light source 401.
[0263] Thus, in the optical scanning device 400, 40 dots can be
written in simultaneously and high-speed printing can be performed.
By increasing the number of the surface-emitting laser elements in
the surface-emitting laser array 100A, high-speed printing is still
more possible.
[0264] Since the life of the surface-emitting laser array 100A
remarkably improves by using the surface-emitting laser elements
1-40, 151-182 for the surface-emitting laser array 100A, the
optical writing unit or light source unit can be made
recyclable.
[0265] In the optical scanning device 400, the light source 401 may
be constituted by the surface-emitting laser array 100 of FIG. 1 or
the surface-emitting laser array 200 of FIG. 14.
[0266] FIG. 26 is a diagram showing the composition of a laser
printer. As shown in FIG. 26, the laser printer 500 includes
photoconductor drum 501, optical scanning device 502, cleaning unit
503, charging unit 504, developing unit 505, transferring unit 506,
and fixing unit 507.
[0267] The optical scanning device 502, the cleaning unit 503, the
charging unit 504, the developing unit 505, the transferring unit
506, and the fixing unit 507 are arranged around the periphery of
the photoconductor drum 501.
[0268] The optical scanning device 502 is constituted by the
optical scanning device 400 shown in FIG. 25, and it forms a latent
image on the photoconductor drum 501 using the multiple laser beams
through the above-mentioned method.
[0269] The cleaning unit 503 removes the toner which remains on the
photoconductor drum 501. The charging unit 504 charges the surface
of the photoconductor drum 501. The developing unit 505 supplies
toner to the surface of the photoconductor drum 501, and carries
out toner development to the latent image formed by the optical
scanning device 502.
[0270] The transferring unit 506 transfers the toner image to a
recording medium. The fixing unit 507 fixes the transferred toner
image to the recording medium.
[0271] In the laser printer 500, upon start of operation, the
charging unit 504 charges the surface of the photoconductor drum
501, and the optical scanning device 502 forms a latent image on
the photoconductor drum 501 by the multiple laser beams.
[0272] And the developing unit 505 supplies toner to the latent
image formed by the optical scanning device 502, to form a toner
image. The transferring unit 506 transfers the toner image to a
recording medium, and the fixing unit 507 fixes the transferred
toner image to the recording medium. Thereby, a toner picture is
transferred on the recording paper 508, after that, a toner image
is heat fused by the fixing unit 507, and formation of an
electrophotographic image is completed.
[0273] On the other hand, an electric discharge unit (not shown)
eliminates the latent image on the surface of the photoconductor
drum 501 by discharging the photoconductor drum surface, and the
cleaning unit 503 removes the toner remaining on the surface of the
photoconductor drum 501. Thereby, the above-mentioned
electrophotographic operation is repeated so that a series of
operation continuously outputs images at high speed. The laser
printer 500 constitutes an image forming device in an embodiment of
the invention.
[0274] FIG. 27 is a diagram showing the composition of an image
forming device. As shown in FIG. 27, the image forming device 600
includes photoconductors 1Y, 1M, 1C, 1K, charging units 2Y, 2M, 2C,
2K, developing units 4Y, 4M, 4C, 4K, cleaning units 5Y, 5M, 5C, 5K,
transferring/charging units 6Y, 6M, 6C, 6K, fixing unit 610,
optical writing unit 620, and transferring belt 630. In FIG. 27, Y
denotes yellow, M denotes magenta, C denotes cyan, and K denotes
black.
[0275] The photoconductors 1Y, 1M, 1C, 1K are rotated in the
direction indicated by the arrow. The charging units 2Y, 2M, 2C,
2K, the developing units 4Y, 4M, 4C, 4K, the transferring/charging
units 6Y, 6M, 6C, 6K, and the cleaning units 5Y, 5M, 5C, 5K are
arranged in the sequence according to the direction of
rotation.
[0276] The charging units 2Y, 2M, 2C, 2K are the components which
uniformly charge the surfaces of the photoconductors 1Y, 1M, 1C,
1K. The surfaces of the photoconductors 1Y, 1M, 1C, 1K between the
charging units 2Y, 2M, 2C, 2K and the developing units 4Y, 4M, 4C,
4K are irradiated by light beams from the optical writing unit 620
(which is constituted by the optical scanning device 400), so that
an electrostatic image is formed on the photoconductors 1Y, 1M, 1C,
1K.
[0277] And the developing units 4Y, 4M, 4C, 4K form toner images on
the surfaces of the photoconductors 1Y, 1M, 1C, 1K based on the
electrostatic images.
[0278] And the transferring/charging units 6Y, 6M, 6C, 6K transfer
the toner image of each color one by one to the recording paper
640. Finally, the fixing unit 610 fixes the transferred image to
the recording paper 640.
[0279] Although a color gap of the respective colors may occur due
to mechanical accuracy etc., the image forming device 600 is
designed for high-density image formation, and can raise the
compensation accuracy of the color gap by adjusting the timing of
turning on of the surface-emitting laser elements of the
surface-emitting laser array used in the optical writing unit
620.
[0280] FIG. 28 is a diagram the composition of an optical
transmitting module. As shown in FIG. 28, the optical transmitting
module 700 includes surface-emitting laser array 701 and optical
fibers 702.
[0281] The surface-emitting laser array 701 is constituted so that
the surface-emitting laser elements 1-40, 151-182 are arranged in
one dimensional formation. The optical fibers 702 are constituted
by a plurality of plastic optical fibers (POF). And the plurality
of plastic optical fibers are arranged corresponding to the
plurality of surface-emitting laser elements 1-40, 151-182 of the
surface-emitting laser array 701.
[0282] In the optical transmitting module 700, the laser beams
emitted from the surface-emitting laser elements 1-40, 151-182 are
transmitted to the corresponding plastic optical fibers,
respectively. And an acryl base plastic optical fiber of has a
bottom of absorption loss at 650 nm, and a 650 nm surface-emitting
laser element is under development. However, it has undesired high
temperature characteristics, and it is not yet put into practical
use.
[0283] An LED (Light Emitting Diode) is used as a light source, but
attaining high-speed modulation is difficult. Use of a
semiconductor laser is needed for realization of high-speed
transmission over 1 Gbps.
[0284] The emission wavelength of the surface-emitting laser
elements 1-40, 151-182 mentioned above is 780 nm. The radiation
characteristic is improved, the high output is provided, and the
high temperature characteristic is good. Although the absorption
loss of the optical fiber is large, the optical transmitting module
700 is usable for short-distance transmission only.
[0285] In the field of optical communications, in order to transmit
a large amount of data simultaneously, a parallel transmission
using a laser array in which a plurality of semiconductor lasers
are integrated is developed. With this technology, high-speed
parallel transmission is possible and simultaneous transmission of
a large amount of data is possible.
[0286] In the optical transmitting module 700, the surface-emitting
laser elements 1-40, 151-182 correspond to the optical fibers
respectively. Alternatively, several surface-emitting laser
elements having different emission wavelengths may be arranged in
one-dimensional or two-dimensional array formation, and the
transmission rate may be increased by performing
wavelength-multiplexing transmission.
[0287] Moreover, the optical transmitting module 700 in which the
surface-emitting laser array using the surface-emitting laser
elements 1-40, 151-182 and the in-expensive POFs are combined makes
it possible to provide a low-cost optical transmitting module and
an optical fiber communications system using the same.
[0288] Since the optical fiber communications system is low cost,
it is effective in the short-distance data communications for the
purpose of home use, office use, in-device use, etc.
[0289] FIG. 29 is a cross-sectional view of a modification of the
surface-emitting laser elements 1-32 of FIG. 1.
[0290] In this embodiment, each of the surface-emitting laser
elements 1-32 of FIG. 1 is constituted by the surface-emitting
laser element 1B of FIG. 29. As shown in FIG. 29, in the
surface-emitting laser element 1B, the resonator spacer layer 103
of the surface-emitting laser element 1 of FIG. 3 is replaced by
the resonator spacer layer 103B, and the other composition is the
same as that of the surface-emitting laser element 1.
[0291] The resonator spacer layer 103B is constituted by non-doped
Ga.sub.0.5In.sub.0.5P and formed on the reflection layer 102. And
Ga.sub.0.5In.sub.0.5P has a thermal conductivity larger than
(Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P which constitutes the
resonator spacer layer 103.
[0292] FIG. 30 is a cross-sectional view showing the neighborhood
of the active layer 104 of the surface-emitting laser element 1B of
FIG. 29. As shown in FIG. 30, the low refractive index layer 1021
of the reflection layer 102 touches the resonator spacer layer
103B. The resonator spacer layer 103B touches the low refractive
index layer 1021 of the reflection layer 102 and the barrier layer
1042 of the active layer 104.
[0293] In the surface-emitting laser element 1B, the resonator
spacer layers 103B and 105 and the active layer 104 constitute a
resonator, and the thickness of the resonator in a direction
perpendicular to the substrate 101 is set to one wavelength
(=.lamda.) of the surface-emitting laser element 1B. That is, the
resonator spacer layers 103B and 105 and the active layer 104
constitute a one-wave resonator.
[0294] The surface-emitting laser array 100 including the
surface-emitting laser elements 1B is produced according to the
manufacturing process of FIGS. 4A-6B. In this case, in the process
of FIG. 4A, Ga.sub.0.5In.sub.0.5P of the resonator spacer layer
103B is formed through the MOCVD method by using trimethyl gallium
(TMG), trimethyl indium (TMI) and phosphine (PH3) as source
materials.
[0295] Since the resonator (=resonator spacer layers 103B and 105
and active layer 104) contains In, it constitutes an absorption
layer which absorbs the difference of the etching depth in the
in-surface direction when forming the mesa structure.
[0296] At the time of production of the surface-emitting laser
array 100 using the surface-emitting laser element 1B, etching for
forming the mesa structure is suspended in the middle of the
resonator (the resonator spacer layer 103B), the difference
.DELTA.d in etching depth between the inter-element portion 120 and
the flat part 130 becomes small.
[0297] Therefore, according to the invention, the difference of the
etching depth in the in-surface direction DR1 of the substrate 101
can be reduced without using dummy elements.
[0298] Since the difference .DELTA.d in etching depth between the
inter-element portion 120 and the flat part 130 is small, the
probability of cutting off of the wires W1-W32 can be lowered.
[0299] Since the pads 51-82 are arranged in the flat part 130, it
is possible to prevent the mesa structure from being damaged by the
pads 51-82 at the time of wire bonding.
[0300] In contrast to the surface-emitting laser element 1, the
surface-emitting laser element 1B is provided so that the resonator
spacer layer 103B is constituted by Ga.sub.0.5In.sub.0.5P having a
thermal conductivity larger than
(Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P, and most of heat
generated in the active layer 104 can be radiated to the substrate
101 side.
[0301] In the above embodiment, the bottom of the mesa structure is
located in the middle of the resonator spacer layer 103B.
Alternatively, the bottom of the mesa structure may be located in
an arbitrary position in the thickness direction of the resonator
(=resonator spacer layers 103B and 105 and active layer 104)
containing In.
[0302] FIG. 31 is a cross-sectional view of a modification of the
surface-emitting laser elements 1-32 of FIG. 1. In this embodiment,
each of the surface-emitting laser elements 1-32 of FIG. 1 is
constituted by the surface-emitting laser element 1C of FIG.
31.
[0303] As shown in FIG. 31, in the surface-emitting laser element
1C, the resonator spacer layer 103 of the surface-emitting laser
element 1 of FIG. 3 is replaced by the resonator spacer layer 103C,
and the other composition is the same as that of the
surface-emitting laser element 1.
[0304] The resonator spacer layer 103C is constituted by non-doped
(Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P/Ga.sub.0.5In.sub.0.5P and
formed on the reflection layer 102.
[0305] FIG. 32 is a cross-sectional view showing the neighborhood
of the active layer 104 of the surface-emitting laser element 1C of
FIG. 31. As shown in FIG. 32, the resonator spacer layer 103C is
constituted by the spacer layers 1031 and 1032. The spacer layer
1031 is formed in contact with the low refractive index layer 1021
of the reflection layer 102, and the spacer layer 1032 is formed in
contact with the barrier layer 1042 of the active layer 104.
[0306] The spacer layer 1031 is constituted by
Ga.sub.0.5In.sub.0.5P. The spacer layer 1032 is constituted by
(Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P.
[0307] In the surface-emitting laser element 1C, the resonator
spacer layers 103C and 105 and the active layer 104 constitute a
resonator, and the thickness of the resonator in a direction
perpendicular to the substrate 101 is set to one wavelength
(=.lamda.) of the surface-emitting laser element 1C. That is, the
resonator spacer layers 103C and 105 and the active layer 104
constitute a one-wave resonator.
[0308] The surface-emitting laser array 100 including the
surface-emitting laser elements 1C is produced according to the
manufacturing process of FIGS. 4A-6B. In this case, in the process
of FIG. 4A,
(Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P/Ga.sub.0.5In.sub.0.5P of
the resonator spacer layer 103C is formed through the MOCVD method
by using trimethyl aluminum (TMA), trimethyl gallium (TMG),
trimethyl indium (TMI) and phosphine (PH3) as source materials.
[0309] Since the resonator (=the resonator spacer layers 103C and
105 and the active layer 104) contains In, it constitutes an
absorption layer which absorbs the difference of the etching depth
in the in-surface direction when forming the mesa structure.
[0310] At the time of production of the surface-emitting laser
array 100 using the surface-emitting laser elements 1C, etching for
forming the mesa structure is suspended in the middle of the
resonator (the resonator spacer layer 103C), and the difference
.DELTA.d in etching depth between the element-arrangement portion
120 and the flat part 130 becomes small.
[0311] Therefore, according to the invention, the difference of the
etching depth in the in-surface direction DR1 of the substrate 101
can be reduced without using a dummy element.
[0312] Since the difference .DELTA.d in etching depth between the
element-arrangement portion 120 and the flat part 130 is small, the
probability of cutting off of the wires W1-W32 can be reduced.
[0313] Since the pads 51-82 are arranged in the flat part 130, it
is possible to prevent the mesa structure from being damaged by the
pads at the time of wire bonding.
[0314] In the surface-emitting laser element 1C, the spacer layer
1032 which touches the active layer 104 among the resonator spacer
layers 103C is constituted by
(Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P which is a wide band gap
material.
[0315] The spacer layer 1031 which touches the low refractive index
layer 1021 (=AlAs) of the reflection layer 102 is constituted by
Ga.sub.0.5In.sub.0.5P. For this reason, in contrast to the
surface-emitting laser element 1, most of heat generated in the
active layer 104 can be radiated to the substrate 101 side, and it
is possible to provide the degree of carrier which is the same as
the degree of carrier included in the surface-emitting laser
element 1.
[0316] In the above embodiment, the bottom of the mesa structure is
located in the middle of resonator spacer layer 103C.
Alternatively, the bottom of the mesa structure may be located in
an arbitrary position in the thickness direction of the resonator
(=the resonator spacer layers 103C and 105 and the active layer
104) containing In.
[0317] FIG. 33 is a cross-sectional view of a modification of the
surface-emitting laser elements 1-32 of FIG. 1.
[0318] In this embodiment, each of the surface-emitting laser
elements 1-32 of FIG. 1 is constituted by the surface-emitting
laser element 1D of FIG. 33. As shown in FIG. 33, in the
surface-emitting laser element 1D, the resonator spacer layer 103
of the surface-emitting laser element 1 of FIG. 3 is replaced by
the resonator spacer layer 103D, and the other composition is the
same as that of the surface-emitting laser element 1.
[0319] The resonator spacer layer 103D is constituted by non-doped
(Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P/AlGaAs and formed on the
reflection layer 102.
[0320] FIG. 34 is a cross-sectional view showing the neighborhood
of the active layer 104 of the surface-emitting laser element 1D of
FIG. 33. As shown in FIG. 34, the resonator spacer layer 103D is
constituted by the spacer layers 1031A and 1032A. The spacer layer
1031A is formed in contact with the low refractive index layer 1021
of the reflection layer 102, and the spacer layer 1032A is formed
in contact with the barrier layer 1042 of the active layer 104.
[0321] The spacer layer 1031A is constituted by AlGaAs having a
thermal conductivity larger than that of
(Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P. The spacer layer 1032A
is constituted by (Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P.
[0322] In the surface-emitting laser element 1D, the resonator
spacer layers 103D and 105 and the active layer 104 constitute a
resonator, and the thickness of the resonator in a direction
perpendicular to the substrate 101 is set to one wavelength
(=.lamda.) of the surface-emitting laser element 1D. That is, the
resonator spacer layers 103D and 105 and the active layer 104
constitute a one-wave resonator.
[0323] The surface-emitting laser array 100 including the
surface-emitting laser elements 1D is produced according to the
manufacturing process of FIGS. 4A-6B. In this case, in the process
of FIG. 4A, (Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P of the
resonator spacer layer 103D is formed through the MOCVD method by
using trimethyl aluminum (TMA), trimethyl gallium (TMG), trimethyl
indium (TMI), and phosphine (PH3) as source materials, and AlGaAs
of the resonator spacer layer 103D is formed by using trimethyl
aluminum (TMA), trimethyl gallium (TMG), and arsine (AsH3) as
source materials.
[0324] Since the spacer layer 1032A of the resonator spacer layer
103D, the active layer 104 and the resonator spacer layer 105
contain In, they constitute an absorption layer which absorbs the
difference of the etching depth in the in-surface direction when
forming the mesa structure.
[0325] At the time of production of the surface-emitting laser
array 100 including the surface-emitting laser elements 1D, etching
for forming the mesa structure is suspended in the middle of the
spacer layer 1032A of the resonator spacer layer 103D, and the
difference .DELTA.d in etching depth between the
element-arrangement portion 120 and the flat part 130 becomes
small.
[0326] Therefore, according to the invention, the difference in
etching depth in the in-surface direction DR1 of the substrate 101
can be reduced without using dummy elements.
[0327] Since the difference .DELTA.d in etching depth between the
element-arrangement portion 120 and the flat part 130 is small, the
probability of cutting off of the wires W1-W32 can be lowered.
Since the pads 51-82 are arranged in the flat part 130, it is
possible to prevent the mesa structure from being damaged by the
pads 51-82 at the time of wire bonding.
[0328] In the surface-emitting laser element 1D, the spacer layer
1032A which touches the active layer 104 among the resonator spacer
layers 103D is constituted by
(Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P which is a wide band gap
material. The spacer layer 1031A which touches the low refractive
index layer 1021 (=AlAs) of the reflection layer 102 is constituted
by AlGaAs.
[0329] Therefore, in contrast to the surface-emitting laser element
1, heat can be more mostly radiated to the substrate 101 side in
the heat which realized the same carrier contained as the degree of
carrier contained in surface-emitting laser element 1, and was
generated in the active layer 104.
[0330] In the above embodiment, the bottom of the mesa structure is
located in the middle of the spacer layer 1032A. Alternatively, the
bottom of the mesa structure may be located in an arbitrary
position in the thickness direction of the spacer layer 1032A
containing In, the active layer 104, and the resonator spacer layer
105.
[0331] FIG. 35 is a cross-sectional view of a modification of
surface-emitting laser elements 1-32 of FIG. 1.
[0332] In this embodiment, each of the surface-emitting laser
elements 1-32 of FIG. 1 is constituted by the surface-emitting
laser element 1E of FIG. 35. As shown in FIG. 35, in the
surface-emitting laser element 1E, the resonator spacer layer 103
and the active layer 104 of the surface-emitting laser element 1 of
FIG. 3 are replaced by the resonator spacer layer 103E and the
active layer 104A, respectively, and the other composition is the
same as that of the surface-emitting laser element 1.
[0333] The resonator spacer layer 103E is constituted by non-doped
AlGaAs and formed on the reflection layer 102. The active layer
104A is constituted by an AlGaAs base material and provided to emit
a 780 nm laser beam.
[0334] In the surface-emitting laser element 1E, the bottom of the
mesa structure is located in the middle of the resonator spacer
layer 105.
[0335] FIG. 36 is a cross-sectional view showing the neighborhood
of the active layer 104A of the surface-emitting laser element 1E
of FIG. 35. As shown in FIG. 36, the resonator spacer layer 103E is
formed in contact with the low refractive index layer 1021 and the
active layer 104A of the reflection layer 102.
[0336] The resonator spacer layer 103E is constituted by
Al.sub.0.6Ga.sub.0.4As. The active layer 104A is constituted by the
quantum well structure in which three well layers 1041A and four
barrier layers 1042A are laminated alternately. Each well layer
1041A is constituted by Al.sub.0.12Ga.sub.0.88As. Each barrier
layer 1042A is constituted by Al.sub.0.3Ga.sub.0.7As.
[0337] In the surface-emitting laser element 1E, the resonator
spacer layers 103E and 105 and the active layer 104A constitute a
resonator, and the thickness of the resonator in a direction
perpendicular to the substrate 101 is set to one wavelength
(=.lamda.) of the surface-emitting laser element 1E. That is, the
resonator spacer layers 103E and 105 and the active layer 104A
constitute a one-wave resonator.
[0338] The surface-emitting laser array 100 including the
surface-emitting laser elements 1E is produced according to the
manufacturing process of FIGS. 4A-6B.
[0339] In this case, in the process of FIG. 4A,
Al.sub.0.6Ga.sub.0.4As of the resonator spacer layer 103E,
Al.sub.0.12Ga.sub.0.8BAs of the well layer 1041A, and
Al.sub.0.3Ga.sub.0.7As of the barrier layer 1042A are formed by
using trimethyl aluminum (TMA), trimethyl gallium (TMG), and arsine
(AsH3) as source materials.
[0340] Since the resonator spacer layer 105 contains In, it
constitutes an absorption layer which absorbs the difference of the
etching depth in the in-surface direction when forming the mesa
structure.
[0341] Since etching for forming the mesa structure is suspended in
the middle of the resonator spacer layer 105 at the time of
production of the surface-emitting laser array 100 including the
surface-emitting laser elements 1E, the difference .DELTA.d in
etching depth between the element-arrangement portion 120 and the
flat part 130 becomes small.
[0342] Therefore, according to the invention, the difference in
etching depth in the in-surface direction DR1 of the substrate 101
can be reduced without using dummy elements.
[0343] Since the difference .DELTA.d in etching depth between the
element-arrangement portion 120 and the flat part 130 is small, the
probability of cutting off of the wires W1-W32 can be lowered.
Since the pads 51-82 are arranged in the flat part 130, it is
possible to prevent the mesa structure from being damaged by the
pads 51-82 at the time of wire bonding.
[0344] In this embodiment, among the reflection layer 102, the
resonator spacer layer 103E, the active layer 104A, the resonator
spacer layer 105, the reflection layer 106, the selective oxidation
layer 107, and the contact layer 108, which constitute the
surface-emitting laser element 1E, only the resonator spacer layer
105 contains In. Alternatively, this embodiment may be configured
so that only the resonator spacer layer 103E contains In or only
the active layer 104A contains In.
[0345] When only the resonator spacer layer 103E contains In, the
resonator spacer layer 103E constitutes an absorption layer which
absorbs the difference of the etching depth in the in-surface
direction when forming the mesa structure, and the bottom of the
mesa structure is located in the middle of the resonator spacer
layer 103E.
[0346] When only the active layer 104A contains In, the active
layer 104A constitutes an absorption layer which absorbs the
difference of the etching depth in the in-surface direction when
forming the mesa structure, and the bottom of the mesa structure is
located in the middle of the active layer 104A.
[0347] In the embodiment mentioned above, the low refractive index
layer 1021 of the reflection layer 102 is constituted by AlAs.
Alternatively, according to the invention, the low refractive index
layer 1021 may be constituted by Al.sub.xGa.sub.1-xAs
(0.9.ltoreq.x.ltoreq.1).
[0348] The surface-emitting laser array of the invention may be
constituted by a plurality of surface-emitting laser elements
arranged in a two-dimensional formation other than the formation of
four rows.times.eight columns.
[0349] The present invention is not limited to the above-described
embodiments, and variations and modifications may be made without
departing from the scope of the present invention.
[0350] The present application is based on and claims the benefit
of priority of Japanese patent application No. 2006-226561, filed
on Aug. 23, 2006, Japanese patent application No. 2006-226562,
filed on Aug. 23, 2006, and Japanese patent application No.
2007-134856, filed on May 22, 2007, the entire contents of which
are hereby incorporated by reference.
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