U.S. patent application number 10/933532 was filed with the patent office on 2005-12-29 for method of producing multi-wavelength semiconductor laser device.
This patent application is currently assigned to Samsung Electro-Mechanics Co., Ltd.. Invention is credited to Lee, Sang Don.
Application Number | 20050286591 10/933532 |
Document ID | / |
Family ID | 35505679 |
Filed Date | 2005-12-29 |
United States Patent
Application |
20050286591 |
Kind Code |
A1 |
Lee, Sang Don |
December 29, 2005 |
Method of producing multi-wavelength semiconductor laser device
Abstract
Disclosed herein is a method for producing a multi-wavelength
semiconductor laser device. The method comprises the steps of:
forming first and second nitride epitaxial layers in parallel on a
substrate for growth of a nitride single crystal; separating the
first and second nitride epitaxial layers from the substrate;
attaching the separated first and second nitride epitaxial layers
to a first conductivity-type substrate; selectively removing the
first and second nitride semiconductor epitaxial layers to expose a
portion of the first conductivity-type substrate and to form first
and second semiconductor laser structures, respectively; and
forming a third semiconductor laser structure on the exposed
portion of the first conductivity-type substrate.
Inventors: |
Lee, Sang Don; (Suwon,
KR) |
Correspondence
Address: |
LOWE HAUPTMAN GILMAN AND BERNER, LLP
1700 DIAGONAL ROAD
SUITE 300 /310
ALEXANDRIA
VA
22314
US
|
Assignee: |
Samsung Electro-Mechanics Co.,
Ltd.
Suwon
KR
|
Family ID: |
35505679 |
Appl. No.: |
10/933532 |
Filed: |
September 3, 2004 |
Current U.S.
Class: |
372/50.12 ;
372/23; 372/50.121 |
Current CPC
Class: |
H01S 5/32341 20130101;
H01S 5/40 20130101; H01S 5/22 20130101; H01S 5/0215 20130101; H01S
5/0217 20130101; H01S 5/4087 20130101; H01S 5/0213 20130101 |
Class at
Publication: |
372/050.12 ;
372/050.121; 372/023 |
International
Class: |
H01S 005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 25, 2004 |
KR |
2004-48079 |
Claims
What is claimed is:
1. A method for producing a multi-wavelength semiconductor laser
device, comprising the steps of: preparing a substrate for growth
of a nitride single crystal thereon; sequentially growing a first
conductivity-type first clad layer, a first active layer and a
second conductivity-type first clad layer on the substrate, to form
a first nitride epitaxial layer; selectively removing the first
nitride epitaxial layer such that a portion of the substrate is
exposed; sequentially growing a first conductivity-type second clad
layer, a second active layer and a second conductivity-type second
clad layer on the exposed portion of the substrate, to form a
second nitride epitaxial layer; separating the first and second
nitride epitaxial layers from the substrate; attaching the
separated first and second nitride epitaxial layers to a first
conductivity-type substrate; selectively etching the first and
second nitride semiconductor epitaxial layers to expose a portion
of the first conductivity-type substrate and to form first and
second semiconductor laser structures from the first and second
nitride epitaxial layers, respectively, the first and second
semiconductor laser structures being separated from each other;
sequentially growing a first conductivity-type third clad layer, a
third active layer and a second conductivity-type third clad layer
on the exposed portion of the first conductivity-type substrate, to
form a third semiconductor laser structure; and forming a first
electrode connected to a bottom surface of the first
conductivity-type substrate and forming second electrodes connected
to the respective second conductivity-type clad layers of the
first, second and third semiconductor laser structures.
2. The method according to claim 1, further comprising the steps
of: selectively etching the respective second conductivity-type
clad layers of the first, second and third semiconductor laser
structures, after the formation of the third semiconductor laser
structure and before the formation of the first electrode and the
second electrodes, to form ridge-shaped layers; and forming an
insulating layer on top surfaces of the second conductivity-type
clad layers except for top ends of the ridge-shaped layers, wherein
the second electrodes are connected to the respective second
conductivity-type clad layers through the respective top ends of
the ridge-shaped layers.
3. The method according to claim 2, wherein the insulating layer is
formed in such a manner that it is extended to side faces of the
first, second and third semiconductor laser structures.
4. The method according to claim 2, wherein the insulating layer is
formed of SiO.sub.2 or Si.sub.3N.sub.4.
5. The method according to claim 1, wherein the separation of the
first and second nitride epitaxial layers from the substrate is
performed by irradiating the bottom surface of the substrate with
laser light to lift-off the first and second nitride epitaxial
layers.
6. The method according to claim 5, wherein the step of separating
the first and second nitride epitaxial layers comprises the
sub-step of lapping the bottom surface of the substrate, before the
laser irradiation, to decrease the thickness of the substrate.
7. The method according to claim 1, wherein the attachment of the
first and second nitride epitaxial layers to the first
conductivity-type substrate is performed by pressuring the first
and second nitride epitaxial layers on a top surface of the first
conductivity-type substrate at high temperature.
8. The method according to claim 1, wherein the etching of the
first nitride semiconductor layer leaves an epitaxial layer for the
first semiconductor laser structure.
9. The method according to claim 1, wherein the step of forming the
third semiconductor laser structure comprises the sub-steps of:
sequentially growing the first conductivity-type third clad layer,
the third active layer and the second conductivity-type third clad
layer on the top surface of the first conductivity-type substrate
on which the first and second semiconductor laser structures are
formed, to form an epitaxial layer for the third semiconductor
laser structure; and selectively etching the epitaxial layer for
the third semiconductor laser structure, to form the third
semiconductor laser structure from the first and second
semiconductor laser structures on a portion of the first
conductivity-type substrate.
10. The method according to claim 1, wherein the first, second and
third semiconductor laser structures are formed in this order from
one side of the first conductivity-type substrate.
11. The method according to claim 1, wherein the substrate for
growth of a nitride single crystal is a sapphire, SiC, or GaN
substrate.
12. The method according to claim 1, wherein the first nitride
epitaxial layer is formed of a GaN-based semiconductor material for
a semiconductor laser structure oscillating blue. light, and the
second nitride epitaxial layer is formed of a GaN-based
semiconductor material for a semiconductor laser structure
oscillating green light.
13. The method according to claim 1, wherein the third
semiconductor laser structure is formed from an epitaxial layer
made of an AlGaInP-based semiconductor material.
14. A multi-wavelength semiconductor laser device comprising: a
first conductivity-type substrate having a top surface divided into
first, second and third regions; a first semiconductor laser
structure oscillating blue light, the first semiconductor laser
structure including a first conductivity-type first GaN-based clad
layer, a first GaN-based active layer and a second
conductivity-type first GaN-based clad layer sequentially formed on
the first region of the first conductivity-type substrate; a second
semiconductor laser structure oscillating green light, the second
semiconductor laser structure including a first conductivity-type
second GaN-based clad layer, a second GaN-based active layer and a
second conductivity-type second GaN-based clad layer sequentially
formed on the second region of the first conductivity-type
substrate; a third semiconductor laser structure including a first
conductivity-type AlGaInP-based clad layer, an AlGaInP-based active
layer and a second conductivity-type AlGaInP-based clad layer
sequentially formed on the third region of the first
conductivity-type substrate; and a first electrode connected to a
bottom surface of the first conductivity-type substrate and second
electrodes connected to the respective second conductivity-type
clad layers of the first, second and third semiconductor laser
structures.
15. The multi-wavelength semiconductor laser device according to
claim 14, wherein the respective second conductivity-type clad
layers of the first, second and third semiconductor laser
structures are formed into ridge-shaped layers, and the first,
second and third semiconductor laser structures further include an
insulating layer formed on top surfaces of the second
conductivity-type clad layers except for top ends of the
ridge-shaped layers, wherein the second electrodes are connected to
the respective second conductivity-type clad layers through the top
ends of the ridge-shaped layers.
16. The multi-wavelength semiconductor laser device according to
claim 15, wherein the insulating layer is formed in such a manner
that it is extended to side faces of the first, second and third
semiconductor laser structures.
17. The multi-wavelength semiconductor laser device according to
claim 15, wherein the insulating layer is formed of SiO.sub.2 or
Si.sub.3N.sub.4.
18. The multi-wavelength semiconductor laser device according to
claim 14, wherein the first, second and third semiconductor laser
structures are formed in this order from one side of the first
conductivity-type substrate.
19. The multi-wavelength semiconductor laser device according to
claim 14, wherein the first conductivity-type substrate is a first
conductivity-type GaAs substrate.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a multi-wavelength
semiconductor laser device, and more particularly to a
multi-wavelength semiconductor laser device capable of
simultaneously or selectively oscillating laser light of three
different wavelengths (e.g., 460 nm, 530 nm and 635 nm), and a
method for producing the multi-wavelength semiconductor laser
device.
[0003] 2. Description of the Related Art
[0004] In general, a semiconductor laser device is one that
produces light amplified by stimulated emission of radiation. The
light produced by the semiconductor laser device has a narrow
frequency width (one of short-wavelength characteristics), superior
directivity and high output. Due to these advantages, the
semiconductor laser device is used as a light source for an optical
pick-up apparatus of an optical disc system, such as a CD (compact
disc) or DVD (digital video disc) player, as well as, is widely
applied to a wide range of fields of optical communications
multiplex communications, space communications and the like.
[0005] In recent years, a multi-wavelength semiconductor laser
device capable of oscillating two or more different wavelengths has
been required in the field of optical discs using laser as a light
source for writing and reading information. For example, a
two-wavelength semiconductor laser device is currently developed as
a light source for both CD players having a relatively low data
density and DVD players having a relatively high data density.
[0006] FIGS. 1a to 1g are cross-sectional views illustrating the
overall procedure of a conventional method for producing a
two-wavelength semiconductor laser device.
[0007] Referring to FIG. 1a, a first semiconductor laser epitaxial
layer oscillating light at a wavelength of 780 nm is formed on an
n-type GaAs substrate 11. Specifically, the first semiconductor
laser epitaxial layer is formed by sequentially growing an n-type
AlGaAs clad layer 12a, an AlGaAs active layer 13a and a p-type
AlGaAs clad layer 14a on the GaAs substrate 11.
[0008] Thereafter, the first semiconductor laser epitaxial layer,
including the layers 12a, 13a and 14a, is selectively removed by
photolithography and etching to expose a portion of a top surface
of the GaAs substrate 11, as shown in FIG. 1b.
[0009] Next, as shown in FIG. 1c, a second semiconductor laser
epitaxial layer oscillating light at a wavelength of 650 nm is
formed on the exposed portion of the GaAs substrate 11 and the
unremoved portion of the first semiconductor laser epitaxial layer.
Specifically, the second semiconductor laser epitaxial layer is
formed by sequentially growing an n-type AlGaInP clad layer 12b, a
GaInP/AlGaInP active layer 13b and a p-type AlGaInP clad layer
14b.
[0010] Thereafter, the second semiconductor laser epitaxial layer,
including the layers 12b, 13b and 14b, formed on the first
semiconductor laser epitaxial layer is removed by photolithography
and etching, and at the same time, the first epitaxial layer is
separated from the second epitaxial layer, as shown in FIG. 1d.
[0011] Next, as shown in FIG. 1e, the p-type AlGaAs clad layer 14a
and the p-type AlGaInP clad layer 14b are selectively etched by a
common process to form ridge-shaped layers 14a' and 14b', which
contribute to an improvement in current injection efficiency. Then,
as shown in FIG. 1f, n-type GaAs current-limiting layers 16a and
16b and p-type GaAs contact layers 17a and 17b are formed.
[0012] Finally, as shown in FIG. 1g, p-side electrodes 19a and 19b
formed of Ti, Pt, Au or an alloy thereof are formed on the p-type
GaAs contact layers 17a and 17b, respectively, and then an n-side
electrode 18 formed of Au/Ge, Au, Ni or an alloy thereof is formed
on a bottom surface of the GaAs substrate 11 to produce the
two-wavelength semiconductor laser device 10.
[0013] In this manner, the semiconductor laser device 10
oscillating light of two different wavelengths is produced on a
single substrate, enabling integration into one chip. Accordingly,
the conventional method is advantageous compared to a method
wherein respective semiconductor laser devices are separately
produced, and are then attached to one substrate by die bonding, in
terms of the following advantages: i) the separate production and
bonding processes are omitted, thus shortening the overall
production procedure, and ii) poor alignment caused during die
bonding of chip can be solved.
[0014] As explained earlier in FIGS. 1a to 1g, the conventional
method is limited to the two-wavelength (650 nm and 780 nm)
semiconductor laser device, and thus cannot be applied to a
three-wavelength (further including light of a short wavelength)
semiconductor laser device. For example, two laser structures
composed of nitride epitaxial layers oscillating light at
wavelengths of 460 nm and 530 nm, and one laser structure composed
of an AlGaInP-based epitaxial layer oscillating light at a
wavelength of 635 nm are required to produce a multi-wavelength
semiconductor laser device oscillating red, green and blue light.
In this connection, there is a problem that since GaN-based
epitaxial layers are particularly required to produce a
semiconductor laser device oscillating light at wavelengths of 460
nm and 530 nm, they cannot be formed on the same substrate,
together with a semiconductor laser structure oscillating light at
a wavelength of 635 nm.
[0015] More specifically, since there is a large difference in the
lattice constant between the AlGaInP epitaxial layer (about 5.6
.ANG.) and the GaN epitaxial layer (about 3.2 .ANG.) for the
semiconductor laser structure oscillating light at a wavelength of
635 nm, it is difficult to grow the AlGaInP and GaN epitaxial
layers on the same substrate. The AlGaInP epitaxial layer can be
formed with superior crystallinity on a GaAs substrate, whereas the
GaN epitaxial layer can be formed with superior crystallinity only
on substrates for growth of a nitride semiconductor, such as GaN,
sapphire and SiC substrates. Consequently, a multi-wavelength
semiconductor laser device oscillating three-color light, for
example, at wavelengths of 460 nm, 530 nm and 635 nm, cannot be
substantially produced by the conventional method for producing a
two-wavelength semiconductor laser device.
SUMMARY OF THE INVENTION
[0016] Therefore, the present invention has been made in view of
the above problems, and it is an object of the present invention to
provide a method for producing a multi-wavelength semiconductor
laser device oscillating light of three different wavelengths by
growing GaN epitaxial layers on a separate substrate, followed by
separation and attachment.
[0017] It is another object of the present invention to provide a
multi-wavelength semiconductor laser device having a novel
structure which is produced by the method.
[0018] In order to accomplish the above objects of the present
invention, there is provided a method for producing a
multi-wavelength semiconductor laser device, comprising the steps
of: preparing a substrate for growth of a nitride single crystal
thereon; sequentially growing a first conductivity-type first clad
layer, a first active layer and a second conductivity-type first
clad layer on the substrate, to form a first nitride epitaxial
layer; selectively removing the first nitride epitaxial layer such
that a portion of the substrate is exposed; sequentially growing a
first conductivity-type second clad layer, a second active layer
and a second conductivity-type second clad layer on the exposed
portion of the substrate, to form a second nitride epitaxial layer;
separating the first and second nitride epitaxial layers from the
substrate; attaching the separated first and second nitride
epitaxial layers to a first conductivity-type substrate;
selectively etching the first and second nitride semiconductor
epitaxial layers to expose a portion of the first conductivity-type
substrate and to form first and second semiconductor laser
structures from the first and second nitride epitaxial layers,
respectively, the first and second semiconductor laser structures
being separated from each other; sequentially growing a first
conductivity-type third clad layer, a third active layer and a
second conductivity-type third clad layer on the exposed portion of
the first conductivity-type substrate, to form a third
semiconductor laser structure; and forming a first electrode
connected to a bottom surface of the first conductivity-type
substrate and forming second electrodes connected to the respective
second conductivity-type clad layers of the first, second and third
semiconductor laser structures.
[0019] In a preferred embodiment of the present invention, the
method of the present invention further comprises the steps of:
selectively etching the respective second conductivity-type clad
layers of the first, second and third semiconductor laser
structures, after the formation of the third semiconductor laser
structure and before the formation of the first electrode and the
second electrodes, to form ridge-shaped layers; and forming an
insulating layer on top surfaces of the second conductivity-type
clad layers except for top ends of the ridge-shaped layers. In this
case, the second electrodes can be connected to the respective
second conductivity-type clad layers through the respective top
ends of the ridge-shaped layers.
[0020] More preferably, the insulating layer may be formed in such
a manner that it is extended to side faces of the first, second and
third semiconductor laser structures. The insulating layer may be
formed of SiO.sub.2 or Si.sub.3N.sub.4.
[0021] In addition, the separation of the first and second nitride
epitaxial layers from the substrate can be performed by irradiating
the bottom surface of the substrate with laser light to lift-off
the first and second nitride epitaxial layers. More preferably, the
method of the present invention may further comprise the step of
lapping the bottom surface of the substrate for growth of a nitride
single crystal, before the laser irradiation, to decrease the
thickness of the substrate.
[0022] Further, the attachment of the first and second nitride
epitaxial layers to the first conductivity-type substrate can be
performed by applying pressure to the first and second nitride
epitaxial layers on a top surface of the first conductivity-type
substrate at high temperature.
[0023] The etching of the first nitride semiconductor layer leaves
only an epitaxial layer for the first semiconductor laser
structure. The formation of the third semiconductor laser structure
can be realized by the sub-steps of: sequentially growing the first
conductivity-type third clad layer, the third active layer and the
second conductivity-type third clad layer on the top surface of the
first conductivity-type substrate on which the first and second
semiconductor laser structures are formed, to form an epitaxial
layer for the third semiconductor laser structure; and selectively
etching the epitaxial layer for the third semiconductor laser
structure, to form the third semiconductor laser structure
separated from the first and second semiconductor laser structures
on a portion of the first conductivity-type substrate.
[0024] Further, in order to facilitate the subsequent growth step,
the first, second and third semiconductor laser structures are
preferably arranged in order that they grow. Namely, it is
preferable that the first, second and third semiconductor laser
structures are formed in this order from one side of the first
conductivity-type substrate.
[0025] The substrate for growth of a nitride single crystal may be
a sapphire, SiC, or GaN substrate, the first nitride epitaxial
layer may be formed of a GaN-based semiconductor material for a
semiconductor laser structure oscillating blue light, and the
second nitride epitaxial layer may be formed of a GaN-based
semiconductor material for a semiconductor laser structure
oscillating green light.
[0026] On the other hand, the third semiconductor laser structure
may be formed of an AlGaInP-based semiconductor material
oscillating red light.
[0027] In accordance with another aspect of the present invention,
there is provided a multi-wavelength semiconductor laser device
having a novel structure. The multi-wavelength semiconductor laser
device comprises: a first conductivity-type substrate having a top
surface divided into first, second and third regions; a first
semiconductor laser structure oscillating blue light, the first
semiconductor laser structure including a first conductivity-type
first GaN-based clad layer, a first GaN-based active layer and a
second conductivity-type first GaN-based clad layer sequentially
formed on the first region of the first conductivity-type
substrate; a second semiconductor laser structure oscillating green
light, the second semiconductor laser structure including a first
conductivity-type second GaN-based clad layer, a second GaN-based
active layer and a second conductivity-type second GaN-based clad
layer sequentially formed on the second region of the first
conductivity-type substrate; a third semiconductor laser structure
including a first conductivity-type AlGaInP-based clad layer, an
AlGaInP-based active layer and a second conductivity-type
AlGaInP-based clad layer sequentially formed on the third region of
the first conductivity-type substrate; and a first electrode
connected to a bottom surface of the first conductivity-type
substrate and second electrodes connected to the respective second
conductivity-type clad layers of the first, second and third
semiconductor laser structures.
[0028] In order to integrate the semiconductor laser structures
composed of the respective epitaxial layers, which are grown under
different conditions, into one chip, the multi-wavelength
semiconductor laser device of the present invention is produced by
forming the respective nitride epitaxial layers for the first and
second semiconductor laser structures oscillating light of short
wavelengths, separating the nitride epitaxial layers from each
other, attaching the separated epitaxial layers to the first
conductivity-type substrate, and forming the third semiconductor
laser structure on the first conductivity-type substrate.
Particularly, according to the method of the present invention,
since the nitride epitaxial layers grown at a relatively high
temperature are formed, separated from the substrate and attached
to the first conductivity-type substrate, unwanted effects
(diffusion of dopants, thermal shock, etc.) of the other layers
during the subsequent epitaxial growth step are reduced. In
addition, since etching is performed to form the semiconductor
laser structures on the same substrate, a multi-wavelength
semiconductor laser device in which the respective laser structures
are highly aligned, can be produced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The above and other objects, features and other advantages
of the present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0030] FIGS. 1a to 1g are cross-sectional views illustrating the
overall procedure of a conventional method for producing a
two-wavelength semiconductor laser device; and
[0031] FIGS. 2a to 2l are cross-sectional views illustrating the
overall procedure of a method for producing a three-wavelength
semiconductor laser device according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] Detailed description will be made of the preferred
embodiment of the present invention with reference to the
accompanying drawings.
[0033] FIGS. 2a to 2l are cross-sectional views illustrating the
overall procedure of a method for producing a three-wavelength
semiconductor laser device according to a preferred embodiment of
the present invention.
[0034] As shown in FIG. 2a, a first nitride epitaxial layer 25a for
a semiconductor laser structure oscillating light of a short
wavelength (e.g., 460 nm) is formed on a sapphire substrate 21. The
first nitride epitaxial layer 25a can be formed by sequentially
growing a first conductivity-type first clad layer 22a, a first
active layer 23a and a second conductivity-type first clad layer
24a. The first conductivity-type first clad layer 22a may be
composed of an n-type Al.sub.0.2Ga.sub.0.8N layer and an n-type GaN
layer, and the second conductivity-type first clad layer 24a may be
composed of a p-type Al.sub.0.2Ga.sub.0.8N layer and a p-type GaN
layer. The active layer 23a may have a multi-quantum well structure
formed of In.sub.0.2Ga.sub.0.8N/I- n.sub.0.05Ga.sub.0.95N.
[0035] Thereafter, as shown in FIG. 2b, the first nitride epitaxial
layer 25a is selectively etched by photolithography and dry etching
such that a portion of the top surface of the substrate 21 is
exposed. The first nitride epitaxial layer 25a is removed in such a
manner that a first semiconductor laser structure 21a remains on
the sapphire substrate 21, but is not limited to the structure
shown in FIG. 2b.
[0036] Next, as shown in FIG. 2c, a second nitride epitaxial layer
25b for a second semiconductor laser structure is formed on the
exposed top surface of the sapphire substrate 21 and the first
semiconductor laser structure 20a. The second nitride epitaxial
layer 25b for a second semiconductor laser structure is formed by
sequentially growing a first conductivity-type second clad layer
22b, a second active layer 23b and a second conductivity-type
second clad layer 24b. In the case where the second nitride
epitaxial layer 25b is designed for a semiconductor laser structure
oscillating light at a wavelength of 530 nm, the first
conductivity-type second clad layer 22b may be composed of an
n-type Al.sub.0.1Ga.sub.0.9N layer and an n-type GaN layer, and the
second conductivity-type second clad layer 24a may be composed of a
p-type Al.sub.0.2Ga.sub.0.8N layer and a p-type GaN layer. The
active layer 23b may have a multi-quantum well structure formed of
In.sub.0.2Ga.sub.0.8N/I- n.sub.0.05Ga.sub.0.95N.
[0037] Additionally, in order to make subsequent separation and
attachment steps easier, the portion of the second nitride
epitaxial layer 25b formed on the first nitride epitaxial layer 25a
is removed, and then the top surface of the first 25a and second
nitride epitaxial layers 25b is planarized, as shown in FIG. 2d, to
form a nitride epitaxial layer 25 for both first and second
semiconductor laser structures.
[0038] The first and second nitride epitaxial layers 25a and 25b
can be formed by conventional growth processes, e.g., metal organic
chemical vapor deposition (MOCVD) and molecular beam epitaxial
(MBE) deposition. Instead of the sapphire substrate 21, known
substrates for growth of a nitride semiconductor, for example, GaN
and SiC substrates, can be used.
[0039] As shown in FIG. 2e, the nitride epitaxial layer 25 is
separated from the sapphire substrate 21. This separation can be
performed by well-known processes, such as lift-off, dry-etching,
lapping and combinations thereof. For example, the lift-off process
using laser light can be performed by irradiating the bottom
surface of the substrate 21 with an Nd-YAG laser at 5 eV or higher
to melt a crystal layer present in the vicinity of the interface
between the nitride epitaxial layer 25 and the sapphire substrate
21, thereby easily lifting-off the nitride epitaxial layer 25. On
the other hand, these dry-etching or lapping processes can be used
to chemically or mechanically separate the sapphire substrate 21.
In addition, the dry-etching or lapping process can be combined
with the lift-off process using laser light. As a preferred
example, the thickness of the substrate 21 is decreased by the
lapping process, and then the nitride epitaxial layer 25 is
separated from the substrate 21 by laser irradiation.
[0040] Next, as shown in FIG. 2f, the separated nitride epitaxial
layer 25 is attached to a first conductivity-type substrate 31. The
first conductivity-type substrate 31 may be an n-type GaAs
substrate suitable as a substrate for growth of an epitaxial layer
to be grown later. This attachment may be performed using a
conductive adhesive, and is preferably performed by applying a
predetermined pressure to the separated nitride epitaxial layer 25
on the first conductivity-type substrate 31 at high temperature.
For example, the nitride epitaxial layer 25 is arranged on the
first conductivity-type substrate 31, and then the resulting
structure is heated at 500.degree. C. for about 20 minutes under a
pressure of at 5 kg/cm.sup.2 to attach the nitride epitaxial layer
25 to the n-type GaAs substrate 31.
[0041] Thereafter, as shown in FIG. 2g, the nitride epitaxial layer
(25 in FIG. 2e) is selectively removed by photolithography and dry
etching to expose portions of the first conductivity-type substrate
31, and at the same time, to form respective first and second
semiconductor laser structures 20a and 20b separated from the first
and the second nitride epitaxial layers 25a and 25b. The top
surface of the first conductivity-type substrate 31 exposed by
etching is provided as a region where a third semiconductor laser
structure is formed through subsequent steps.
[0042] Specifically, a first conductivity-type third clad layer
22c, a third active layer 23c and a second conductivity-type third
clad layer 24c are sequentially grown on the exposed surface of the
first conductivity-type substrate 31 such that the first and the
second semiconductor laser structures 20a and 20b are separated
from each other. In this manner, a third semiconductor laser
structure 20c is formed on the first conductivity-type substrate
(see, FIG. 2i).
[0043] The formation of the third semiconductor laser structure
will be explained below with reference to FIGS. 2h and 2i.
[0044] Next, an epitaxial layer 25c for the third semiconductor
laser structure is formed on the first conductivity-type substrate
31 on which the first and second semiconductor laser structures 20a
and 20b are formed, as shown in FIG. 2h. The epitaxial layer 25c
for the third semiconductor laser structure can be formed by
sequentially growing the first conductivity-type third clad layer
22c, the third active layer 23c and the second conductivity-type
third clad layer 24c. In the case where the epitaxial layer 25c is
designed for a semiconductor laser structure oscillating light at a
wavelength of 635 nm, the first and second conductivity-type third
clad layers 22c and 24c may be composed of n-type and p-type
(Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5P layers, respectively. The
active layer 23c may have a multi-quantum well structure composed
of an InGaP/(Al.sub.0.5Ga.sub.0.5).sub.0.5In.sub.0.5P layer.
[0045] Thereafter, as shown in FIG. 2i, the AlGaInP-based epitaxial
layer 25c is selectively etched in such a manner that the third
semiconductor laser structure 20c is formed on one region of the
top surface of the first conductivity-type substrate 31 except for
the regions where the first and second semiconductor laser
structures 20a and 20b are formed. Portions of the AlGaInP-based
epitaxial layer 25c formed on the top surfaces of the first and the
second semiconductor laser structures 20a and 20b and between the
respective semiconductor laser structures 20a, 20b and 20c are
selectively removed by etching, such that the first, second and
third semiconductor laser structures 20a, 20b and 20c are separated
from one another.
[0046] In addition, etching is preferably performed to form the
respective second conductivity-type clad layers 24a, 24b and 24c of
the first, the second and the third semiconductor laser structures
20a, 20b and 20c into ridge-shaped layers 24a', 24b' and 24c', as
shown in FIG. 2j. The width between the ridge-shaped layers may be
about 2 .mu.m to about 7 .mu.m. This ridge structure can increase
the efficiency of current injected through the second
conductivity-type clad layers 24a, 24b and 24c.
[0047] Next, as shown in FIG. 2k, an insulating layer 32 is formed
on the top surfaces of the second conductivity-type clad layers
24a, 24b and 24c except for top ends of the ridge-shaped layers.
The insulating layer 32 acts as a current-limiting layer.
Preferably, the insulating layer 32 may be formed in such a manner
that it is extended to side faces of the first, second and third
semiconductor laser structures and the overall faces of the
substrate 31. Thus, the insulating layer 32 can be used as a common
passivation layer, as well as a current-limiting layer. The
insulating layer 32 may be formed of SiO.sub.2 or
Si.sub.3N.sub.4.
[0048] Referring finally to FIG. 2l, a first electrode 38 is formed
on a bottom surface of the first conductivity-type substrate 31,
and second electrodes 39a, 39b and 39c are formed in such a manner
that they are connected to the respective second conductivity-type
clad layers 24a, 24b and 24c of the first, second and third
semiconductor laser structures 20a, 20b and 20c. In this
embodiment, the second electrodes 39a, 39b and 39c can be formed on
top surfaces of the respective semiconductor laser structures 20a,
20b and 20c such that they are connected to the respective second
conductivity-type clad layers 24a, 24b and 24c through the tops
surfaces of the ridge-shaped layers. The first electrode 38 may be
formed of AuGe, Au, Ni or an alloy thereof, and the second
electrodes 39a, 39b and 39c may be formed of at least one metal
selected from the group consisting of Ti, Pt, Ni and Au. In this
manner, a three-wavelength semiconductor laser device 30 in which
the three semiconductor laser structures 20a, 20b and 20c
oscillating light of the respective inherent wavelengths are
arranged on the same substrate 31, can be produced.
[0049] As shown in FIG. 21, according to the semiconductor laser
device 30 capable of oscillating three-wavelength light of the
three primary colors (red, green and blue), the first semiconductor
laser structure 20a formed of a first GaN-based material, the
second semiconductor laser structure 20b formed of a second
GaN-based material, and the third semiconductor laser structure 20c
formed of an AlGaIn-based material can be integrated into one chip.
The first and second semiconductor laser structures 20a and 20b are
grown on a separate substrate for growth of a nitride
semiconductor, separated from the substrate and attached to the
first conductivity-type substrate 31. For easy growth of the third
semiconductor laser structure 20c, the first semiconductor laser
structure 20a is preferably arranged at one side of the first
conductivity-type substrate 31. Furthermore, the second and third
semiconductor laser structures 20b and 20c are preferably arranged
in this order in order that they grow from the side where the first
semiconductor laser structure 20a is arranged.
[0050] In the case where ridge-shaped layers and a current-limiting
layer are employed, the insulating layer 32 of the respective
second conductivity-type clad layers 24a, 24b and 24c is provided
as a current-limiting layer. Since the second conductivity-type
first clad layers (formed of a GaN-based material) are grown under
different conditions, a conventional current-limiting layer formed
by reverse attachment has a limitation in its simultaneous
formation on the three semiconductor laser structures. Accordingly,
the present invention suggests the use of the insulating layer 32
as a current-limiting layer to simultaneously form the
current-limiting layer on the three semiconductor laser structures.
The insulating layer is extended to side faces of the respective
semiconductor laser structures, and thus acts as a passivation
layer of the respective semiconductor laser structures.
[0051] Although the present invention has been described herein
with reference to the foregoing examples and the accompanying
drawings, the scope of the present invention is defined by the
claims that follow. Accordingly, those skilled in the art will
appreciate that various substitutions, modifications and changes
are possible, without departing from the technical spirit of the
present invention as disclosed in the accompanying claims. It is to
be understood that such substitutions, modifications and changes
are within the scope of the present invention.
[0052] As apparent from the above description, according to the
method for producing a multi-wavelength semiconductor laser device
oscillating red, green and blue light, after first and second
GaN-based semiconductor laser structures are grown in parallel on a
substrate for growth of a nitride semiconductor, separated from the
substrate and attached to a first conductivity-type substrate
(e.g., a GaAs substrate), another semiconductor laser structure
oscillating light of a different wavelength is formed on the first
conductivity-type substrate. Accordingly, the semiconductor laser
structures, which cannot be grown on a single substrate, can be
integrated into one chip.
[0053] In addition, since epitaxial layers for the respective
semiconductor laser structures are formed on the final substrate,
the three-wavelength semiconductor laser device can be produced in
a simpler manner, without causing poor alignment during attachment
of the semiconductor laser structures.
* * * * *