U.S. patent application number 12/781175 was filed with the patent office on 2011-06-09 for vertical cavity surface emitting laser, vertical cavity surface emitting laser device, optical transmission device, and information processing apparatus.
This patent application is currently assigned to FUJI XEROX CO., LTD.. Invention is credited to Kazuyuki Matsushita, Kazutaka Takeda, Masahiro Yoshikawa.
Application Number | 20110135318 12/781175 |
Document ID | / |
Family ID | 44082134 |
Filed Date | 2011-06-09 |
United States Patent
Application |
20110135318 |
Kind Code |
A1 |
Takeda; Kazutaka ; et
al. |
June 9, 2011 |
VERTICAL CAVITY SURFACE EMITTING LASER, VERTICAL CAVITY SURFACE
EMITTING LASER DEVICE, OPTICAL TRANSMISSION DEVICE, AND INFORMATION
PROCESSING APPARATUS
Abstract
A vertical cavity surface emitting laser that includes: a
substrate; a first semiconductor multilayer reflector; an active
region; a second semiconductor multilayer reflector; a columnar
structure formed from the second semiconductor multilayer reflector
to the first semiconductor multilayer reflector; a current
narrowing layer formed inside of the columnar structure and having
a conductive region surrounded by an oxidization region; a first
electrode formed at a top of the columnar structure, electrically
connected to the second semiconductor multilayer reflector and
defining a beam window; a first insulating film comprised of a
material with a first refractive index and formed on the first
electrode to cover the beam window; and a second insulating film
comprised of a material with a second refractive index and formed
on the first insulating film, of which a radius is smaller than a
radius of the conductive region.
Inventors: |
Takeda; Kazutaka; (Kanagawa,
JP) ; Yoshikawa; Masahiro; (Kanagawa, JP) ;
Matsushita; Kazuyuki; (Kanagawa, JP) |
Assignee: |
FUJI XEROX CO., LTD.
Tokyo
JP
|
Family ID: |
44082134 |
Appl. No.: |
12/781175 |
Filed: |
May 17, 2010 |
Current U.S.
Class: |
398/182 ;
257/E33.005; 257/E33.067; 369/100; 372/50.1; 438/31; G9B/7 |
Current CPC
Class: |
H01S 5/18311 20130101;
H01S 5/005 20130101; H01S 5/18391 20130101; H01S 5/02212 20130101;
H01S 2301/166 20130101; H01S 2301/176 20130101; H01S 5/04254
20190801 |
Class at
Publication: |
398/182 ;
372/50.1; 438/31; 369/100; 257/E33.005; 257/E33.067; G9B/7 |
International
Class: |
H04B 10/04 20060101
H04B010/04; H01S 5/183 20060101 H01S005/183; H01L 33/00 20100101
H01L033/00; G11B 7/00 20060101 G11B007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 9, 2009 |
JP |
2009-279328 |
Claims
1. A vertical cavity surface emitting laser comprising: a
substrate; a first semiconductor multilayer reflector of a first
conductive type formed on the substrate; an active region formed on
the first semiconductor multilayer reflector; a second
semiconductor multilayer reflector of a second conductive type
formed on the active region; a columnar structure that is formed
from the second semiconductor multilayer reflector to the first
semiconductor multilayer reflector on the substrate; a current
narrowing layer that is formed inside of the columnar structure,
and has a conductive region surrounded by an oxidization region
selectively oxidized; a first electrode that is annular, is formed
at a top of the columnar structure, is electrically connected to
the second semiconductor multilayer reflector, and defines a beam
window; a first insulating film that is comprised of a material
which has a first refractive index capable of transmitting an
oscillation wavelength, and formed on the first electrode to cover
the beam window; and a second insulating film that is circular, is
comprised of a material which has a second refractive index that is
able to transmit an oscillation wavelength and greater than the
first refractive index, and is formed on the first insulating film,
and of which a radius is smaller than a radius of the conductive
region.
2. The vertical cavity surface emitting laser according to claim 1,
wherein a third refractive index to an oscillation wavelength of a
semiconductor layer which composes the second semiconductor
multilayer reflector is greater than the second refractive
index.
3. The vertical cavity surface emitting laser according to claim 1,
further comprising a third insulating layer that covers a sidewall
and a part of a top of the columnar structure, wherein an opening
to connect to the first electrode is formed between the third
insulating film and the first insulating film.
4. The vertical cavity surface emitting laser according to claim 3,
wherein the third insulating film is comprised of a same material
as that of the second insulating film.
5. The vertical cavity surface emitting laser according to claim 1,
wherein the radius of the conductive region is at least 5
.mu.m.
6. A fabrication method of a vertical cavity surface emitting laser
having a columnar structure on a substrate, the fabrication method
comprising: stacking a semiconductor layer including a first
semiconductor multilayer reflector of a first conductive type, an
active region, a current narrowing layer which is conductive, a
second semiconductor multilayer reflector of a second conductive
type on the substrate; forming a first electrode which is annular
and defines a beam window on the second semiconductor multilayer
reflector; forming a first insulating film that is comprised of a
material having a first refractive index to an oscillation
wavelength on the first electrode to cover a beam window of the
first electrode; forming the columnar structure including the first
electrode and the first insulating film at a top on the substrate
by etching the semiconductor layer from the second semiconductor
multilayer reflector to the first semiconductor multilayer
reflector; forming an oxidization region and a conductive region
surrounded by the oxidization region inside of a current narrowing
layer by oxidizing the current narrowing layer inside of the
columnar structure selectively; forming a second insulating film
that is comprised of a material having a second refractive index
that is greater than the first refractive index on whole area of
the substrate including the columnar structure; and forming a
pattern of the second insulating film that corresponds to a center
of the conductive region and is smaller than a radius of the
conductive region, and an opening that exposes the first electrode
on the first insulating film by removing the second insulating film
at the top of the columnar structure selectively.
7. The fabrication method according to claim 7 wherein a third
refractive index to an oscillation wavelength of a semiconductor
layer composing the second semiconductor multilayer reflector is
greater than the second refractive index.
8. A vertical cavity surface emitting laser device comprising: a
vertical cavity surface emitting laser including: a substrate; a
first semiconductor multilayer reflector of a first conductive type
formed on the substrate; an active region formed on the first
semiconductor multilayer reflector; a second semiconductor
multilayer reflector of a second conductive type formed on the
active region; a columnar structure that is formed from the second
semiconductor multilayer reflector to the first semiconductor
multilayer reflector on the substrate; a current narrowing layer
that is formed inside of the columnar structure, and has a
conductive region surrounded by an oxidization region selectively
oxidized; a first electrode that is annular, is formed at a top of
the columnar structure, is electrically connected to the second
semiconductor multilayer reflector, and defines a beam window; a
first insulating film that is comprised of a material which has a
first refractive index capable of transmitting an oscillation
wavelength, and formed on the first electrode to cover the beam
window; and a second insulating film that is circular, is comprised
of a material which has a second refractive index that is able to
transmit an oscillation wavelength and greater than the first
refractive index, and is formed on the first insulating film, and
of which a radius is smaller than a radius of the conductive
region; and an optical member that receives a beam from the
vertical cavity surface emitting laser.
9. An optical transmission device comprising: a vertical cavity
surface emitting laser device that comprises: a vertical cavity
surface emitting laser that includes: a substrate; a first
semiconductor multilayer reflector of a first conductive type
formed on the substrate; an active region formed on the first
semiconductor multilayer reflector; a second semiconductor
multilayer reflector of a second conductive type formed on the
active region; a columnar structure that is formed from the second
semiconductor multilayer reflector to the first semiconductor
multilayer reflector on the substrate; a current narrowing layer
that is formed inside of the columnar structure, and has a
conductive region surrounded by an oxidization region selectively
oxidized; a first electrode that is annular, is formed at a top of
the columnar structure, is electrically connected to the second
semiconductor multilayer reflector, and defines a beam window; a
first insulating film that is comprised of a material which has a
first refractive index capable of transmitting an oscillation
wavelength, and formed on the first electrode to cover the beam
window; and a second insulating film that is circular, is comprised
of a material which has a second refractive index that is able to
transmit an oscillation wavelength and greater than the first
refractive index, and is formed on the first insulating film, and
of which a radius is smaller than a radius of the conductive
region; and an optical member that receives a beam from the
vertical cavity surface emitting laser; and a transmission unit
that transmits a laser beam emitted from the vertical cavity
surface emitting laser device through an optical medium.
10. An information processing apparatus comprising: a vertical
cavity surface emitting laser that includes: a substrate; a first
semiconductor multilayer reflector of a first conductive type
formed on the substrate; an active region formed on the first
semiconductor multilayer reflector; a second semiconductor
multilayer reflector of a second conductive type formed on the
active region; a columnar structure that is formed from the second
semiconductor multilayer reflector to the first semiconductor
multilayer reflector on the substrate; a current narrowing layer
that is formed inside of the columnar structure, and has a
conductive region surrounded by an oxidization region selectively
oxidized; a first electrode that is annular, is formed at a top of
the columnar structure, is electrically connected to the second
semiconductor multilayer reflector, and defines a beam window; a
first insulating film that is comprised of a material which has a
first refractive index capable of transmitting an oscillation
wavelength, and formed on the first electrode to cover the beam
window; and a second insulating film that is circular, is comprised
of a material which has a second refractive index that is able to
transmit an oscillation wavelength and greater than the first
refractive index, and is formed on the first insulating film, and
of which a radius is smaller than a radius of the conductive
region; a focusing unit that focuses a laser beam emitted from the
vertical cavity surface emitting laser onto a record medium; and a
structure which scans the laser beam focused by the focusing unit
on the record medium.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based on and claims priority under 35
USC 119 from Japanese Patent Application No. 2009-279328 filed on
Dec. 9, 2009.
BACKGROUND
[0002] (i) Technical Field
[0003] The present invention relates to a vertical cavity surface
emitting laser, a vertical cavity surface emitting laser device, an
optical transmission device, and an information processing
apparatus.
[0004] (ii) Related Art
[0005] A vertical cavity surface emitting laser (VCSEL) is used as
a light source in a communication device and an image forming
apparatus. Single lateral mode, high power and long service life
are required for such vertical cavity surface emitting laser used
as a light source. In an exemplary selective oxidation type
vertical cavity surface emitting laser, a single lateral mode is
achieved by reducing a radius of the oxidized aperture of a current
narrowing layer to about 2 through 3 .mu.m, but it becomes
difficult to obtain an optical output greater than or equal to 3 mW
stably.
SUMMARY
[0006] According to an aspect of the present invention, there is
provided a vertical cavity surface emitting laser device including:
a substrate; a first semiconductor multilayer reflector of a first
conductive type formed on the substrate; an active region formed on
the first semiconductor multilayer reflector; a second
semiconductor multilayer reflector of a second conductive type
formed on the active region; a columnar structure that is formed
from the second semiconductor multilayer reflector to the first
semiconductor multilayer reflector on the substrate; a current
narrowing layer that is formed inside of the columnar structure,
and has a conductive region surrounded by an oxidization region
selectively oxidized; a first electrode that is annular, is formed
at a top of the columnar structure, is electrically connected to
the second semiconductor multilayer reflector, and defines a beam
window; a first insulating film that is comprised of a material
which has a first refractive index capable of transmitting an
oscillation wavelength, and formed on the first electrode to cover
the beam window; and a second insulating film that is circular, is
comprised of a material which has a second refractive index that is
able to transmit an oscillation wavelength and greater than the
first refractive index, and is formed on the first insulating film,
and of which a radius is smaller than a radius of the conductive
region.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Exemplary embodiments of the present invention will be
described in detail based on the following figures, wherein:
[0008] FIG. 1 illustrates a plane view, and a cross-section view
taken from line A-A of a vertical cavity surface emitting laser in
accordance with a first exemplary embodiment of the present
invention;
[0009] FIG. 2 is a cross-section view enlarging a top of a mesa of
the vertical cavity surface emitting laser illustrated in FIG.
1;
[0010] FIG. 3 is a diagram illustrating exemplary combinations of a
first insulating film and a second insulating film;
[0011] FIG. 4A is a diagram illustrating a simulation result of a
reflection ratio of an upper DBR in a region where only a first
insulating film exists, and FIG. 4B is a diagram illustrating a
simulation result of a reflection ratio of an upper DBR in a region
where a first insulating film and a second insulating film are
stacked;
[0012] FIG. 5 is a cross-section view enlarging a top of a mesa of
a vertical cavity surface emitting laser in accordance with a
second exemplary embodiment of the present invention;
[0013] FIGS. 6A and 6B are cross-section views for explaining a
fabrication process of a vertical cavity surface emitting laser in
accordance with a third exemplary embodiment of the present
invention;
[0014] FIGS. 7A and 7B are cross-section views for explaining a
fabrication process of a vertical cavity surface emitting laser in
accordance with the third exemplary embodiment of the present
invention;
[0015] FIGS. 8A and 8B are schematic cross-section views
illustrating a composition of a vertical cavity surface emitting
laser device in which the vertical cavity surface emitting laser of
exemplary embodiments and an optical component are packaged;
[0016] FIG. 9 is a diagram illustrating a composition of a light
source device using the vertical cavity surface emitting laser of
exemplary embodiments; and
[0017] FIG. 10 is a schematic cross-section view illustrating a
composition of an optical transmission device using the vertical
cavity surface emitting laser device illustrated in FIG. 8A.
DETAILED DESCRIPTION
[0018] A description will now be given, with reference to the
accompanying drawings, of exemplary embodiments of the present
invention. In the following description, a selective oxidation type
vertical cavity surface emitting laser will be exemplified, and a
vertical cavity surface emitting laser is abbreviated as a VCSEL.
The scale in drawings is exaggerated to understand the feature of
the present invention, and is not same as the scale of actual
devices.
First Exemplary Embodiment
[0019] FIG. 1 is a schematic cross-section view of a VCSEL in
accordance with the first exemplary embodiment of the present
invention. As illustrated in FIG. 1, a VCSEL 10 of the exemplary
embodiment is formed by stacking an n-type lower Distributed Bragg
Reflector (hereinafter, abbreviated as DBR) 102, an active region
104, and a p-type upper DBR 106 on an n-type GaAs substrate 100.
The n-type lower DBR 102 is formed by stacking AlGaAs layers with
different Al composition alternately. The active region 104
includes a quantum well layer sandwiched between upper and lower
spacer layers. The p-type upper DBR 106 is formed by stacking
AlGaAs layers with different Al composition on the active region
104 alternately.
[0020] The n-type lower DBR 102 is a multi-layer stack formed by a
pair of an Al0.9Ga0.1As layer and an Al0.3Ga0.7As layer for
example. The thickness of each layer is .lamda./4n.sub.r (.lamda.
is an oscillation wavelength, and n.sub.r is a refractive index of
the medium), and the Al.sub.0.9Ga.sub.0.1As layer and the
Al.sub.0.3Ga.sub.0.7As layer are stacked alternately 40 periods. A
carrier concentration after doping an n-type impurity (silicon) is
3.times.10.sup.18 cm.sup.-3 for example.
[0021] A lower spacer layer of the active region 104 is an undoped
Al0.6Ga0.4As layer, quantum well active layers are an undoped
Al0.11Ga0.89As quantum well layer and an undoped Al0.3Ga0.7As
barrier layer, and an upper spacer layer is an undoped Al0.6Ga0.4As
layer.
[0022] The p-type upper DBR 106 is a multi-layer stack formed by a
pair of an Al0.9Ga0.1As layer and an Al0.3Ga0.7As layer for
example. The thickness of each layer is .lamda./4n.sub.r, and the
Al.sub.0.9Ga.sub.0.1As layer and the Al.sub.0.3Ga.sub.0.7As layer
are stacked alternately 24 periods. A carrier concentration after
doping a p-type impurity (carbon) is 3.times.10.sup.18 cm.sup.-3
for example. A contact layer 106A comprised of p-type GaAs is
formed at a top layer of the upper DBR 106, and a current narrowing
layer 108 comprised of p-type AlAs is formed at a bottom layer of
the upper DBR 106 or inside of the upper DBR 106.
[0023] A cylindrical mesa (a columnar structure) M is formed on the
substrate 100 by etching a semiconductor layer from the upper DBR
106 to the lower DBR 102. The current narrowing layer 108 is
exposed on the side surface of the mesa M, and has an oxidization
region 108A which is selectively oxidized from the side surface,
and a conductive region (oxidized aperture) 108B surrounded by the
oxidization region 108A. In the oxidization process of the current
narrowing layer 108, the oxidation rate of an AlAs layer is faster
than that of an AlGaAs layer, and the oxidization proceeds from the
side surface of the mesa M to the inside at an almost constant
rate. Therefore, the planar shape of the surface, which is parallel
to the principal surface of the substrate 100 of the conductive
region 108B, becomes a round shape which reflects the outer shape
of the mesa M, and the center of the conductive region 108B
corresponds to the axial center of the mesa M which means an
optical axis. The radius of the conductive region 110B may have the
size at which the high-order lateral mode oscillation occurs. For
example, the radius of the conductive region 110B may be equal to
or larger than 5 .mu.m in a wavelength range of 780 nm.
[0024] An annular metallic p-side electrode 110 is formed at the
top layer of the mesa M. The p-side electrode 110 is comprised of a
metal formed by stacking Au or Ti/Au for example, and is ohmic
connected to the contact layer 106A of the upper DBR 106. The
outside diameter of the p-side electrode 110 is larger than the
radius of the conductive region 108B. The circular opening is
formed at the center of the p-side electrode 110, and this opening
defines a beam window 110A which emits a beam. The center of the
beam window 110A corresponds to the optical axis of the mesa M, and
the radius of the beam window 110A is larger than the radius of the
conductive region 108B.
[0025] A circular first insulating film 112 is formed on the p-side
electrode 110 to cover the beam window 110A. The first insulating
film 112 is comprised of a material that is able to transmit the
oscillation wavelength. The outside diameter of the first
insulating film 112 is smaller than the outside diameter of the
p-side electrode, and larger than the radius of the beam window
110A. Therefore, the beam window 110A is covered by the first
insulating film 112 completely, but a part of the p-side electrode
110 is exposed by the first insulating film 112.
[0026] An interlayer insulating film 114 covering the edge of the
bottom, side, and top of the mesa M is formed. The edge of the
interlayer insulating film 114 covers the part of the p-side
electrode 110, and a annular contact hole 116 which exposes the
p-side electrode 110 is formed between the interlayer insulating
film 114 and the first insulating film 112.
[0027] A circular second insulating film 118 comprised of a
material that is able to transmit the oscillation wavelength is
formed on the first insulating film 112. The center of the second
insulating film 118 corresponds to the optical axis, and the
outside diameter of the second insulating film 118 is smaller than
the radius of the conductive region 108B. For example, when the
radius of the conductive region 108B is about 5 .mu.m, the radius
of the second insulating film 118 is about 3 .mu.m. In the
preferable exemplary embodiment, the second insulating film 118 can
be formed with the same process as that of the interlayer
insulating film 114 by using the same material as that of the
interlayer insulating film 114. An n-side electrode 120 that is
electrically connected to the lower DBR 102 is formed on the back
side of the substrate 100.
[0028] FIG. 2 is an enlarged cross-section views of the top of the
mesa of the VCSEL in FIG. 1. In the present exemplary embodiment,
the refractive index of the first insulating film 112 is n1, the
refractive index of the second insulating film 118 is n2, the
refractive index of the semiconductor layer (the contact layer
106A) of the upper DBR 106 is n3. Then, the relation among n1, n2,
and n3 is n1<n2<n3. Each film thickness of the first
insulating film 112 and the second insulating film 118 is odd
multiples of the wavelength of the medium .lamda./4, which means
(2n-1).lamda./4 (n is positive integer).
[0029] As illustrated in FIG. 2, there are a circular first region
Z1 where the first insulating film 112 is formed and the second
insulating film 118 is stacked on the first insulating film 112,
and an annular second region X2 where only the first insulating
film 112 is formed around the first region Z1, on the contact layer
106A exposed by the beam window 110A. The center of the first
region Z1 corresponds to the center of the conductive region 110B
(the optical axis), but the size of the first region Z1 is smaller
than the radius of the conductive region 110B. As the second
insulating film 118 of which the refractive index n2 is greater
than the refractive index n1 of the first insulating film 112 is
formed in the first region Z1, the reflection ratio r1 of the upper
DBR 106 including the first region Z1 is higher than the reflection
ratio r2 of the upper DBR 106 including the second region Z2.
Therefore, a high-order lateral mode oscillation is suppressed in
the upper DBR 106 including the second region Z2, and a fundamental
transverse mode oscillation is accelerated in the upper DBR 106
including the first region Z1. Therefore, it is possible to
increase the optical output by making the radius of the conductive
region 108B (the radius of the oxidized aperture) be the size at
which a high-order lateral mode oscillates.
[0030] Preferably, it is desirable to select a material that makes
the difference between the refractive indexes n1 and n2 large. This
makes it possible to make a difference of reflection ratio between
the first region Z1 and the first region Z2 (r1-r2) large. For
example, the first insulating film 112 may be comprised of SiON,
and the second insulating film 118 may be comprised of SiN. In
addition to this, the first insulating film 112 and the second
insulating film 118 may be comprised of combinations indicated in
FIG. 3. For example, when the first insulating film 112 is
comprised of SiON, the second insulating film 118 may be comprised
of TiO.sub.2. When the first insulating film 112 is comprised of
SiO.sub.2, the second insulating film 118 may be comprised of
SiN.
[0031] A description will now be given of a simulation result of a
reflection ratio of the upper DBR of the VCSEL of the present
exemplary embodiment. Suppose that the upper DBR 106 is composed by
stacking Al.sub.0.9Ga.sub.0.1As layer and Al.sub.0.3Ga.sub.0.7As
layer 24 periods. FIG. 4A illustrates a reflection ratio r2 of the
upper DBR including the second region Z2 when SiON with a film
thickness of .lamda./4 is formed as the first insulating film 112.
FIG. 4B illustrates a reflection ratio r1 of the upper DBR
including the first region Z1 when SiON with a film thickness of
.lamda./4 is formed as the first insulating film 112, and SiN with
a film thickness of .lamda./4 is formed as the second insulating
film 118. In the second region Z2 illustrated in FIG. 4A, the
reflection ratio r2 is about 99.2% in a wavelength range of 780 nm.
In the first region Z1 illustrated in FIG. 4B, the reflection ratio
r1 is about 99.7% in a wavelength range of 780 nm. A reflection
ratio needed for a laser oscillation typically is about 99.5%.
Therefore, in the first region Z1, the fundamental lateral mode
generated on the optical axis is easily oscillated, and in the
second region Z2 the high-order lateral mode oscillation away from
the optical axis is suppressed. The fundamental transverse mode
oscillation is selectively accelerated and the high-order lateral
mode oscillation is suppressed, by making the difference between
reflection ratios r1 of the first region Z1 and r2 of the second
region Z2. Ordinary skilled persons in the art can understand that
it is possible to adjust reflection ratios r1 and r2 by selecting
the periodic number of the upper DBR 106 and materials of first and
second insulating films 112 and 118.
Second Exemplary Embodiment
[0032] FIG. 5 is a cross-section view of a main part of a VCSEL in
accordance with a second exemplary embodiment of the present
invention. In a VCSEL 10A in accordance with the present exemplary
embodiment, a taper is formed in the mesa M, and the radius of the
mesa gradually narrows along to the top. Such taper of the mesa can
be formed by selecting proper etching condition. In addition to the
taper of the mesa M, the end surface of the first insulating film
112, the end surface of the interlayer insulating film 114, and the
end surface of the second insulating film 118 are inclined in a
tapered shape. By making the mesa M have a taper structure, the
step coverage of the adherent interlayer insulating film 114 is
improved, and it is possible to prevent the disconnection of the
interlayer insulating film 114. In addition, it is possible to make
the film thickness of the interlayer insulating film 114 that is
formed on the side and top of the mesa M almost uniform. When the
second insulating film 118 is formed with the same process as that
of the interlayer insulating film 114, it is possible to
uniformly-control both film thicknesses to be odd multiples of
.lamda./4. Furthermore, it is possible to prevent the disconnection
of metallic wiring that is coupled to the p-side electrode 110
through the contact hole 116.
Third Exemplary Embodiment
[0033] A description will now be given of a third exemplary
embodiment. The third exemplary embodiment relates to a preferable
fabrication method of the VCSEL. A fabrication method is described
with reference to FIGS. 6A through 7B. As illustrated in FIG. 6A,
the n-type lower DBR 102, the active region 104, and the p-type
upper DBR 106 are stacked on the n-type GaAs substrate 100 by the
metal organic chemical vapor deposition (MOCVD) method. The n-type
lower DBR 102 is composed by stacking Al.sub.0.9Ga.sub.0.1As and
Al.sub.0.3Ga.sub.0.7As with a carrier concentration of
2.times.10.sup.18 cm.sup.-3 alternately 40 periods so that each
film thickness becomes quarter of the wavelength of the medium. The
active regionl04 is comprised of an undoped Al.sub.0.6Ga.sub.0.4As
lower spacer layer, an undoped Al.sub.0.11Ga.sub.0.89As quantum
well layer, an undoped Al.sub.0.3Ga.sub.0.7As barrier layer, and an
undoped Al.sub.0.6Ga.sub.0.4As upper spacer layer. The p-type upper
DBR 106 is composed by stacking a p-type Al.sub.0.9Ga.sub.0.1As
layer and a p-type Al.sub.0.3Ga.sub.0.7As layer with a carrier
concentration of 3.times.10.sup.18 cm.sup.-3 alternately 24 periods
so that each film thickness becomes quarter of the wavelength of
the medium. The p-type GaAs contact layer 106A with a carrier
concentration of 1.times.10.sup.19 cm.sup.-3 is formed at the top
layer of the upper DBR 106, and a p-type AlAs layer is formed at
the bottom of the upper DBR 106 or inside of the upper DBR 106. It
is not illustrated, but a buffer layer may be provided between the
substrate 100 and the lower DBR 102.
[0034] A resist pattern is formed on the contact layer 106A by the
photolithography process conventionally known, and the annular
p-side electrode 110 comprised of Au/Ti is formed on the contact
layer 106A by the liftoff process. Then, SiON is deposited on whole
surface of the substrate 100 by CVD, and the circular first
insulating film 112 covering the beam window 110A which is the
opening of the p-side electrode 110 is formed by patterning SiON.
At this time, the inside of the p-side electrode 110 is covered by
the first insulating film 112, and the outside is exposed. The beam
window 110A is protected from an exposure and particles generated
in subsequent processes by being covered by the first insulating
film 112.
[0035] As illustrated FIG. 6B, a circular mask MK1 is formed on a
region including the p-side electrode 110 and the first insulating
film 112 by the photolithography process. Then, a cylindrical mesa
M is formed by etching a semiconductor layer from the upper DBR 106
to the lower DBR 102 by the reactive ion etching process using
boron trichloride for example. Accordingly, an AlAs layer 108
inside of the upper DBR 106 is exposed on the side surface of the
mesa M. Then the oxidization process that exposes the substrate to
the water-vapor atmosphere with a temperature of 340.degree. C. for
a given time is carried out, and the oxidization region 108A which
is oxidized a certain distance from the side surface of the mesa M
is formed inside of the AlAs layer 108. The oxidation control is
performed so that a radius of plane field of the conductive region
108B surrounded by the oxidization region 108A becomes larger than
the radius needed for a conventional single lateral mode (e.g. 3
.mu.m), and becomes the size at which the high-order lateral mode
occurs (e.g. 5 .mu.m).
[0036] Then, the mask MK1 is removed, and the interlayer insulating
film 114 comprised of SiN is formed on whole surface of the
substrate as illustrated in FIG. 7A. The interlayer insulating film
114 is adjusted so that the film thickness of the top of the mesa M
becomes quarter of the wavelength of the medium. Then, as
illustrated in FIG. 7B, a mask MK2 is formed by the
photolithography process, and the interlayer insulating film 114
exposed by the mask MK2 is removed by etching. Preferably, the
interlayer insulating film 114 is etched under the etching
condition that the selectivity between the interlayer insulating
film 114 and the first insulating film 112 can be selected. For
example, the reactive ion etching process using an etchant of
SF.sub.6+O.sub.2 is carried out. According to this, patterns of the
contact hole 116 and the second insulating film 118 to the p-side
electrode 110 is formed at the top of the mesa M. Then, a metallic
wiring that is coupled to the p-side electrode 110 through the
contact hole 116 is formed, and the n-side electrode is formed on
the back side of the substrate.
[0037] According to the fabrication method of the present exemplary
embodiment, it is possible to form the second insulating film 118
with an easy process only changing a mask pattern by forming the
second insulating film 118 and the interlayer insulating film 114
simultaneously, and mass production at low cost becomes possible.
In addition, as the process is processed under the condition that
the beam window 110A is protected by the first insulating film 112,
this makes it work for the reliability of the VCSEL. When the
insulating layer is formed inside of the contact layer by etching
the contact layer, it is difficult to stop the etching with high
accuracy. If the film thickness of the etched layer is not uniform,
there is a possibility that a reflection ratio changes, and this
makes it difficult to obtain a reproducible composition.
[0038] In above exemplary embodiments, a description was given of a
current narrowing layer comprised of AlAs, but a current narrowing
layer may be an AlGaAs layer of which the Al composition is higher
than the Al composition of other DBRs. In addition, the radius of
the conductive region (the oxidized aperture) of the current
narrowing layer can be changed appropriately according to required
optical output. Furthermore, in above exemplary embodiments, the
description was given of an GaAs-based VCSEL, but the present
invention can be applied to other VCSELs using other III-V group
compound semiconductors. In above exemplary embodiments, the
description was given of a single spot VCSEL, but the VCSEL can be
a multi-spot VCSEL where multiple mesas (emission portion) are
formed on the substrate, or a VCSEL array.
[0039] A description will be given of a vertical cavity surface
emitting laser device, an optical information processing apparatus,
and an optical transmission device using the VCSEL of exemplary
embodiments with reference to drawings. FIG. 8A is a cross-section
view illustrating a composition of a vertical cavity surface
emitting laser device in which the VCSEL and an optical component
are packaged. A vertical cavity surface emitting laser device 300
fixes a chip 310, on which a long resonator VCSEL is formed, to a
disk-shaped metal stem 330 via a conductive bond 320. Conductive
leads 340 and 342 are inserted in a through hole (not illustrated)
provided to the stem 330, the lead 340 is electrically connected to
the n-side electrode of the VCSEL, and the lead 342 is electrically
connected to the p-side electrode.
[0040] A rectangular hollow cap 350 is fixed on the stem 330
including the chip 310, and a ball lens 360 is fixed in an opening
352 located in the center of the cap 350. The ball lens 360 is laid
out so that the optical axis of the ball lens 360 corresponds to
the substantial center of the chip 310. When a forward current is
applied between leads 340 and 342, a laser beam is emitted from the
chip 310 to the vertical direction. The distance between the chip
310 and the ball lens 360 is adjusted so that the ball lens 360 is
included within the spread angle .theta. of the laser beam from the
chip 310. A light receiving element and a temperature sensor to
monitor the emitting condition of the VCSEL can be included in the
cap.
[0041] FIG. 8B is a diagram illustrating a composition of another
vertical cavity surface emitting laser device. A vertical cavity
surface emitting laser device 302 illustrated in FIG. 8B fixes a
plane glass 362 in the opening 352 located in the center of the cap
350 instead of using the ball lens 360. The plane glass 362 is laid
out so that the center of the plane glass 362 corresponds to the
substantial center of the chip 310. The distance between the chip
310 and the plane glass 362 is adjusted so that the opening radius
of the plane glass 362 becomes equal to or larger than the spread
angle .theta. of the laser beam from the chip 310.
[0042] FIG. 9 is a diagram illustrating a case where the VCSEL is
applied to a light source of an optical information processing
apparatus. An optical information processing apparatus 370 is
provided with a collimator lens 372 which receives the laser beam
from the vertical cavity surface emitting laser device 300 or 302,
in which the long resonator VCSEL is packaged, illustrated in FIG.
8A or 8B, a polygon mirror 374 which rotates at constant speed and
reflects a beam of light from the collimator lens 372 at constant
spread angle, a f.theta. lens 376 which receives the laser beam
from the polygon mirror 374 and irradiates the laser beam to a
reflection mirror 378, the linear reflection mirror 378, and a
photoreceptor drum (a record medium) 380 which forms latent images
based on the reflection beam from the reflection mirror 378. As
described above, the laser beam from the VCSEL can be used as a
light source of the optical information processing apparatus such
as a copier and a printer provided with an optical system which
focuses the laser beam from the VCSEL onto the photoreceptor drum
and a structure which scans the focused laser beam on the
photoreceptor drum.
[0043] FIG. 10 is a cross-section view illustrating a composition
where the vertical cavity surface emitting laser device illustrated
in FIG. 8A is applied to an optical transmission device. An optical
transmission device 400 includes a cylindrical chassis 410 fixed to
the stem 330, a sleeve 420 integrally-formed on the end surface of
the chassis 410, a ferrule 430 held in an opening 422 of the sleeve
420, and an optical fiber 440 held by the ferrule 430. The end
portion of the chassis 410 is fixed to a flange 332 which is
circumferentially-formed of the stem 330. The ferrule 430 is laid
out in the opening 422 of the sleeve 420 accurately, and the
optical axis of the optical fiber 440 is matched to the optical
axis of the ball lens 360. The core of the optical fiber 440 is
held in a through hole 432 of the ferrule 430.
[0044] The laser beam emitted from the surface of the chip 310 is
focused by the ball lens 360. The focused beam enters to the core
of the optical fiber 440, and is transmitted. In above exemplary
embodiments, the ball lens 360 is used, but other lenses such as a
biconvex lens and a plane-convex lens can be used besides a ball
lens. Furthermore, the optical transmission device 400 can include
a drive circuit to apply an electrical signal to leads 340 and 342.
The optical transmission device 400 can also include a receiving
function to receive an optical signal through the optical fiber
440.
[0045] The foregoing description of the exemplary embodiments of
the present invention has been provided for the purposes of
illustration and description. It is not intended to be exhaustive
or to limit the invention to the precise forms disclosed.
Obviously, many modifications and variations will be apparent to
practitioners skilled in the art. The exemplary embodiments were
chosen and described in order to best explain the principles of the
invention and its practical applications, thereby enabling others
skilled in the art to understand the invention for various
exemplary embodiments and with the various modifications as are
suited to the particular use contemplated. It is intended that the
scope of the invention be defined by the following claims and their
equivalents.
* * * * *