U.S. patent application number 11/022892 was filed with the patent office on 2005-07-14 for nitride semiconductor laser device and method for fabrication thereof.
This patent application is currently assigned to Sharp Kabushiki Kaisha. Invention is credited to Kamikawa, Takeshi, Kaneko, Yoshika.
Application Number | 20050151153 11/022892 |
Document ID | / |
Family ID | 34737104 |
Filed Date | 2005-07-14 |
United States Patent
Application |
20050151153 |
Kind Code |
A1 |
Kamikawa, Takeshi ; et
al. |
July 14, 2005 |
Nitride semiconductor laser device and method for fabrication
thereof
Abstract
In a nitride semiconductor light-emitting device, and according
to a method for fabricating it, a low-defect region having a defect
density of 10.sup.6 cm.sup.-2 or less and a carved region in the
shape of a depressed portion are formed on the surface of a nitride
semiconductor substrate, and the etching angle .theta., which is
the angle between the side surface portion of the depressed portion
and an extension line of the bottom surface portion thereof as
measured with the depressed portion seen in a sectional view, is in
a range of 75.degree..ltoreq..theta..ltor- eq.140.degree.. This
prevents the development of cracks, and reduces the creep-up growth
from the bottom growth portion of the carved region, thereby
reducing the film thickness of the side growth portion. This makes
it possible to produce, with a high yield, a nitride semiconductor
laser device having a nitride semiconductor growth layer with good
surface flatness.
Inventors: |
Kamikawa, Takeshi;
(Mihara-shi, JP) ; Kaneko, Yoshika;
(Funabashi-shi, JP) |
Correspondence
Address: |
Barry E. Bretschneider
Morrison & Foerster LLP
Suite 300
1650 Tysons Boulevard
McLean
VA
22102
US
|
Assignee: |
Sharp Kabushiki Kaisha
Osaka
JP
|
Family ID: |
34737104 |
Appl. No.: |
11/022892 |
Filed: |
December 28, 2004 |
Current U.S.
Class: |
257/103 |
Current CPC
Class: |
H01S 5/0207 20130101;
H01S 5/32025 20190801; H01S 2304/12 20130101; H01L 33/20 20130101;
H01S 5/320225 20190801; H01S 2301/176 20130101; H01L 33/32
20130101; H01S 5/2201 20130101; H01S 5/32341 20130101 |
Class at
Publication: |
257/103 |
International
Class: |
H01L 029/22 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 5, 2004 |
JP |
2004-000328 |
Claims
What is claimed is:
1. A nitride semiconductor light-emitting device comprising: a
nitride semiconductor substrate of which at least part of a surface
is formed from a nitride semiconductor; and a nitride film
semiconductor growth layer laid on the surface of the nitride
semiconductor substrate, wherein a low-defect region having a
defect density of 10.sup.6 cm.sup.-2 or less and a carved region in
a shape of a depressed portion are formed on the surface of the
nitride semiconductor substrate, and wherein an etching angle
.theta., which is an angle between a side face portion of the
depressed portion and an extension line of a bottom face portion
thereof as measured with the depressed portion seen in a sectional
view, is in a range of
75.degree..ltoreq..theta..ltoreq.140.degree..
2. The nitride semiconductor light-emitting device according to
claim 1, wherein the etching angle .theta. is in a range of
85.degree..ltoreq..theta..ltoreq.140.degree..
3. The nitride semiconductor light-emitting device according to
claim 1, wherein, of all layers constituting the nitride film
semiconductor growth layer, a layer that makes contact with the
surface of the nitride semiconductor substrate is a GaN layer, and
this GaN layer is 2 .mu.m or less thick.
4. The nitride semiconductor light-emitting device according to
claim 1, wherein, of all layers constituting the nitride film
semiconductor growth layer, a layer that makes contact with the
surface of the nitride semiconductor substrate is an AlGaN
layer.
5. The nitride semiconductor light-emitting device according to
claim 1, wherein the carved region is 1 .mu.m or more but 30 .mu.m
or less deep.
6. The nitride semiconductor light-emitting device according to
claim 1, wherein a laser stripe that is formed in the nitride film
semiconductor growth layer so as to function as a light-emitting
portion is formed above the low-defect region and elsewhere than
above the carved region.
7. The nitride semiconductor light-emitting device according to
claim 6, wherein the laser stripe is formed 20 .mu.m or more away
from the carved region.
8. The nitride semiconductor light-emitting device according to
claim 1, wherein a side growth portion formed, as part of the
nitride film semiconductor growth layer, on a side face of the
carved region is 20 .mu.m or less thick.
9. A method for fabricating a nitride semiconductor light-emitting
device, the method including a step of forming a nitride film
semiconductor growth layer on a surface of a nitride semiconductor
substrate of which at least part is formed from a nitride
semiconductor and that includes on the surface thereof a low-defect
region having a defect density of 10.sup.6 cm.sup.-2 or less, the
method comprising: a first step of forming a carved region by
etching the nitride semiconductor substrate; and a second step of
laying the nitride film semiconductor growth layer on the nitride
semiconductor substrate that has undergone the first step, wherein,
in the first step, an etching angle .theta., which is an angle
between a side face portion of a depressed portion formed as the
carved region and an extension line of a bottom face portion of the
depressed portion, is in a range of
75.degree..ltoreq..theta..ltoreq.140.degree..
10. The method for fabricating a nitride semiconductor
light-emitting device according to claim 9, wherein, in the first
step, the etching angle .theta. is in a range of
85.degree..ltoreq..theta..ltoreq.140.degre- e..
11. The method for fabricating a nitride semiconductor
light-emitting device according to claim 9, wherein, in the second
step, a layer that makes contact with the surface of the nitride
semiconductor substrate is a 2 .mu.m or less thick GaN layer.
12. The method for fabricating a nitride semiconductor
light-emitting device according to claim 9, wherein, in the second
step, a layer that makes contact with the surface of the nitride
semiconductor substrate is an AlGaN layer.
13. The method for fabricating a nitride semiconductor
light-emitting device according to claim 9, the method further
comprising: a step of forming a laser stripe in the nitride film
semiconductor growth layer, above the low-defect region and
elsewhere than above the carved region, so as to function as a
light-emitting portion.
14. The method for fabricating a nitride semiconductor
light-emitting device according to claim 13, wherein the laser
stripe is formed 20 .mu.m or more away from the carved region.
15. The method for fabricating a nitride semiconductor
light-emitting device according to claim 9, wherein a side growth
portion formed, as part of the nitride film semiconductor growth
layer, on a side face of the carved region is 20 .mu.m or less
thick.
16. The method for fabricating a nitride semiconductor
light-emitting device according to claim 9, wherein, in the first
step, first a nitride semiconductor layer is grown on the nitride
semiconductor substrate, and then the carved region is formed.
Description
[0001] This nonprovisional application claims priority under 35
U.S.C. .sctn. 119(a) on Patent Application No. 2004-000328 filed in
Japan on Jan. 5, 2004, the entire contents of which are hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a nitride semiconductor
laser device, and to a method for fabricating a nitride
semiconductor laser device. More particularly, the present
invention relates to a nitride semiconductor laser device that uses
as the substrate thereof a nitride semiconductor.
[0004] 2. Description of Related Art
[0005] One feature of nitride semiconductors, for example GaN,
AlGaN, GaInN, and AlGaInN, is that they have higher band gap
energies than AlGaInAs-based and AlGaInP-based semiconductors.
Another feature of such nitride semiconductors is that they are
direct-transition semiconductor materials.
[0006] Having these features, nitride semiconductors have recently
been receiving much attention as materials for building
semiconductor light-emitting devices, such as semiconductor lasers
that emit light in a short-wavelength region ranging from
ultraviolet (blue) to green and light-emitting diodes that emit
light in a wide wavelength range covering from ultraviolet (blue)
to red. With this trend, various applications of nitride
semiconductors have been researched and developed in the fields of
high-density optical disks, full-color displays, environmental and
medical equipment, and many other fields.
[0007] Nitride semiconductors have also been arousing expectations
as materials for building high-output high-frequency electronic
devices that can operate at high temperatures. Moreover, nitride
semiconductors have higher thermal conductivity than GaAs-based or
other semiconductors, and are thus expected to find applications in
devices that operate at high temperatures and at high outputs.
Furthermore, nitride semiconductors do not require materials
comparable with arsenic (As) used in AlGaAs-based semiconductors or
cadmium (Cd) used in ZnCdSSe-based semiconductors, or materials
from which such materials are obtained, such as arsine (AsH.sub.3).
Thus, nitride semiconductors are also expected as compound
semiconductor materials that are environment-friendly.
[0008] However, conventionally, the fabrication of nitride
semiconductors suffers from extremely low yields, meaning that,
relative to the total number of nitride semiconductor laser devices
fabricated on a single wafer, the number of usable ones is very
small. One reason for low yields is the development of cracks in
the nitride semiconductor growth layer. Cracks may develop both
from faults in the substrate and from faults in the nitride
semiconductor growth layer laid on top of the substrate.
[0009] Theoretically, it is desirable that a nitride semiconductor
growth layer, such as one formed from GaN, be grown and formed on a
GaN substrate. To date, however, there has been developed no
high-quality GaN single crystal substrate of which the lattice
matches with that of GaN. For this reason, as substrates of which
the lattice constant differs comparatively little from that of GaN,
SiC substrates are occasionally used instead.
[0010] However, SiC substrates are expensive, are difficult to form
in large diameters, and are liable to produce tensile strains, with
the result that they are more liable to develop cracks. In
addition, any material for the substrate of a nitride semiconductor
is required to withstand a growth temperature as high as about
1,000.degree. C. and be resistant to discoloration and corrosion in
the atmosphere of ammonia gas, which is the material for GaN.
[0011] For the reasons discussed above, it is sapphire substrates
that are typically used as substrates on top of which to lay a
nitride semiconductor growth layer. However, a sapphire substrate
exhibits comparatively severe lattice mismatch (about 13%). To
overcome this, on top of a sapphire substrate, a buffer layer
formed from GaN, AlN, or the like is formed by low-temperature
growth, and then, on top of the buffer layer, a nitride
semiconductor growth layer is grown. Even this cannot completely
eliminate strains, with the result that cracks still develop
depending on the composition and film thickness of the growth layer
and other conditions.
[0012] To overcome this, according to one conventionally proposed
method for fabricating a nitride semiconductor device using a GaN
substrate, a nitride semiconductor laser device is produced by
using a GaN substrate that has previously been so processed as to
minimize the effects of such regions thereon as exhibit poor
crystallinity (Japanese Patent Application Laid-Open as No.
2003-124573 on Apr. 25, 2003, hereinafter referred to as Patent
Publication 1).
[0013] However, it is not only from faults in the substrate that
cracks develop. When a nitride semiconductor laser device is
produced, a nitride semiconductor growth layer is laid on top of a
substrate. Here, the nitride semiconductor growth layer is composed
of different kinds of film, such as GaN, AlGaN, InGaN, etc. Since
these individual films of which the nitride semiconductor growth
layer is composed have different lattice constants, lattice
mismatch arises, resulting in the development of cracks.
[0014] To overcome this, according to another conventionally
proposed method, after the growth of a nitride semiconductor growth
layer, depressions are formed on the surface thereof, without the
surface being made flat. This helps reduce cracks (Japanese Patent
Application Laid-Open as No. 2002-246698 on Aug. 30, 2002,
hereinafter referred to as Patent Publication 2).
[0015] By this method, it is possible to reduce both cracks that
develop from faults in the substrate and cracks that develop from
lattice mismatch between the individual films of which the nitride
semiconductor growth layer formed on top of the substrate is
composed.
[0016] In a case where, as described above, a nitride semiconductor
laser device is produced by using a previously processed substrate,
the nitride semiconductor growth layer thereof is structured as
shown in FIG. 7.
[0017] Specifically, on top of the etched surface of an n-type GaN
substrate 60 (see FIGS. 6A and 6B), a nitride semiconductor growth
layer 11 is formed as described below.
[0018] For example, on top of the n-type GaN substrate 60, the
following layers are laid on top of one another in the order named:
a 2.0 .mu.m thick n-type GaN layer 70; a 1.5 .mu.m thick n-type
Al.sub.0.062Ga.sub.0.938N first clad layer 71; a 0.2 .mu.m thick
n-type Al.sub.0.1Ga.sub.0.9N second clad layer 72; a 0.1 .mu.m
thick n-type Al.sub.0.062Ga.sub.0.938N third clad layer 73; a 0.1
.mu.m thick n-type GaN guide layer 74; a multiple quantum well
active layer 75 composed of three pairs of a 4 nm thick InGaN layer
and a 8 nm thick GaN layer laid on top of one another; a 20 nm
thick p-type Al.sub.0.3Ga.sub.0.7N evaporation prevention layer 76;
a 0.08 .mu.m thick p-type GaN guide layer 77; a 0.5 .mu.m thick
p-type Al.sub.0.062Ga.sub.0.938N clad layer 78; and a 0.1 .mu.m
thick p-type GaN contact layer 79.
[0019] In this way, by laying the nitride semiconductor growth
layer 11 on the previously processed n-type GaN substrate 60 by
MOCVD (metal organic chemical vapor deposition), a nitride
semiconductor wafer having depressions on the surface of the
semiconductor growth layer 11 as shown in FIGS. 6A and 6B is
produced.
[0020] In crystallography, it is customary to add an overscore to
the absolute value of the index indicating a plane or orientation
of a crystal if the index is negative. However, in the present
specification, since such notation is impossible, a negative index
will be indicated by placing the minus sign "-" in front of the
absolute value thereof.
[0021] In the present specification, some terms are used in
specific senses. A "trough" denotes a depressed portion formed in
the shape of a stripe on the surface of a previously processed
substrate as shown in FIGS. 6A and 6B. A "ridge" denotes an
elevated portion formed likewise in the shape of a stripe.
[0022] A "previously processed substrate" denotes a substrate
produced by forming troughs and ridges on the surface of a nitride
semiconductor substrate or on the surface of a nitride
semiconductor growth layer laid on top of the surface of a nitride
semiconductor substrate.
[0023] In the n-type GaN substrate 60 shown in FIGS. 6A and 6B,
stripe-shaped troughs are formed in the [1-100] direction by a dry
etching technique such as RIE (reactive ion etching). These troughs
are 5 .mu.m wide, are 3 .mu.m deep, and are formed with a period of
400 .mu.m between adjacent troughs. On top of the so etched n-type
GaN substrate 60, the nitride semiconductor growth layer 11, having
a multiple-layer structure as shown in FIG. 7, is formed by a
growth method such as MOCVD.
[0024] However, producing a nitride semiconductor laser device by
the technique disclosed in Patent Publication 2 mentioned above,
specifically by using a previously processed GaN substrate and
epitaxially growing a nitride semiconductor growth layer on top of
the substrate by MOCVD or the like, has been confirmed to
contribute indeed to the reduction of cracks but not to a
satisfactory improvement in yields.
[0025] This is because the depressions left on the nitride
semiconductor growth layer degrade the flatness of the films of
which it is composed. With degraded flatness, the individual layers
have thicknesses varying from one place to another within the
nitride semiconductor growth layer. This causes the characteristics
(such as FFP (far-field pattern), threshold current, and slope) of
the produced nitride semiconductor laser devices vary from one
device to another. This reduces the number of devices of which the
characteristics fall within the desired ranges. Thus, to improve
yields, it is necessary not only to reduce the development of
cracks but also to improve the flatness of the individual
films.
[0026] FIG. 8 shows the flatness, as actually measured in the
[1-100] direction, of the surface of a nitride semiconductor wafer
formed as shown in FIGS. 6A, 6B, and 7. The measurements were taken
under the following conditions: measurement length=600 .mu.m;
measurement duration=3 s; probe needle pressure=30 mg; and
horizontal resolution=1 .mu.m per sample. The graph in FIG. 8 shows
that, within the 600 .mu.m wide region in which the measurements
were taken, the level difference between the highest and lowest
points was 200 nm.
[0027] This variation in flatness results from the fact that, as
shown in FIG. 6B, the film thicknesses of the individual layers of
the nitride semiconductor growth layer 11 laid on top of the
surface of the n-type GaN substrate 60 vary from one place to
another within the wafer.
[0028] Consequently, the characteristic of nitride semiconductor
laser devices greatly vary according to where on the surface of a
wafer they are produced. Moreover, the thickness of the Mg-doped
p-type layer (i.e., the sum of the layer thicknesses from the
p-type GaN guide layer 77 through the p-type GaN contact layer 79),
which thickness greatly affects the characteristic of nitride
semiconductor laser devices, greatly varies according to where on
the surface of the substrate it is formed.
[0029] In the process of forming a ridge structure as a
current-narrowing structure, whereas ridges are left in the shape
of 2 .mu.m wide stripes, the rest is etched off by a dry etching
technique using an ICP (inducting coupled plasma) machine.
[0030] Thus, if the thickness of the p-type layer before etching
varies from one place to another within the wafer surface, the film
thickness of the p-type layer that remains after etching, which
thickness most greatly affects the characteristics of nitride
semiconductor laser devices, accordingly varies greatly from one
place to another within the wafer surface.
[0031] Because of the factors discussed above, the layer thickness
varies among individual nitride semiconductor laser devices. In
addition, even within a single nitride semiconductor laser device,
while the thickness of the remaining p-type layer is almost zero at
some places, it is considerably great at other places. This
variation in the thickness of the remaining p-type layer greatly
affects the characteristics, including the life, of nitride
semiconductor laser devices.
[0032] Next, using a light interference microscope, the thickness
of the p-type layer before a ridge structure was formed by etching
was measured. Here, with the design value of the thickness set at
0.700 .mu.m, 20 measurements were taken respectively at different
places within the wafer surface, and the mean deviation .sigma. of
those measurements were calculated. The mean deviation .sigma.
indicates the variation of the film thickness among the 20
measurements thereof. The greater the mean deviation .sigma., the
greater the variation of the various characteristic, such as FFP
(far-field pattern), threshold current, and slope efficiency, of
nitride semiconductor laser devices.
[0033] The mean deviation .sigma. of the thickness of the p-type
layer formed on the wafer produced by growing the nitride
semiconductor growth layer 11 on top of the conventional n-type GaN
substrate 60 as shown in FIGS. 6A and 6B was 0.07. To
satisfactorily reduce the variation of the characteristics of
nitride semiconductor laser devices, the mean deviation .sigma.
needs to be reduced to 0.01 or lower. The mean deviation .sigma. of
the thickness of the p-type layer formed on the wafer produced by
growing the nitride semiconductor growth layer 11 shown in FIGS. 6A
and 6B, however, does not meet this requirement. Incidentally, the
mean deviation is calculated by adding together the differences of
the individual values of the 20 measurements of the layer thickness
from the mean value of the 20 measurements and then dividing the
result by 20.
[0034] This large variation in layer thickness within the wafer
surface is considered to result from the fact that, when the films
are epitaxially grown in the ridge portions of the previously
processed substrate, their growth speed is affected by the troughs,
resulting in uneven growth.
[0035] Specifically, as shown in FIG. 9A, on the n-type GaN
substrate 60 having troughs formed thereon, as epitaxial growth
progresses, a top growth portion 90, a side growth portion 91, and
a bottom growth portion 92 grow in an uncarved region 93, in the
side face 94 of a carved region, and in the bottom face 95 of the
carved region, respectively.
[0036] When a semiconductor thin film is grown in this way, the
side growth portion 91, indicated with hatching in FIG. 9A, greatly
affects the flatness of the top growth portion 90. As shown in FIG.
9A, let the film thickness of the side growth portion 91 be X.
[0037] It has been confirmed that, as the growth of the
semiconductor thin film in the side growth portion 91 progresses as
shown in FIG. 9B, the growth speed of the semiconductor thin film
in the top growth portion 90 is affected to vary.
[0038] Specifically, the larger the film thickness X of the side
growth portion 91, the lower the growth speed of the semiconductor
thin film on the top growth portion 90, and thus the smaller the
film thickness on the top growth portion 90. By contrast, the
smaller the film thickness X of the side growth portion 91, the
higher the growth speed of the semiconductor thin film on the top
growth portion 90, and thus the greater the film thickness on the
top growth portion 90. Thus, the film thickness of the
semiconductor thin film on the surface of the top growth portion 90
varies greatly according to the film thickness X of the side growth
portion 91.
[0039] The film thickness X of the side growth portion 91 varies
from one place to another in the [1-100] direction because of the
variation of the off angle within the surface, unevenness in the
substrate itself such as the variation of the curvature thereof
within the surface, unevenness of the epitaxial growth speed within
the substrate surface, unevenness of the carving process within the
substrate surface, and other factors. As a result, as discussed
above, the flatness, within the wafer surface, of the semiconductor
thin film laid on the surface of the top growth portion 90 is
degraded.
[0040] Moreover, the greater the film thickness X of the side
growth portion 91, the greater the variation, within the substrate
surface, of the film thickness X of the side growth portion 91, and
thus the more the flatness within the wafer surface is degraded.
Thus, to obtain good flatness, the film thickness X of the top
growth portion 90 needs to be reduced.
[0041] Moreover, the semiconductor thin film in the side growth
portion 91 not only epitaxially grows directly on the side face,
but its growth is also promoted by "creep-up growth," whereby the
semiconductor thin film grown in the bottom growth portion 92
creeps up to the side growth portion 91.
[0042] FIG. 10 is a conceptual diagram illustrating how creep-up
growth occurs from the bottom growth portion 92 of the carved
region to the side growth portion 91. This creep-up growth further
increases the film thickness X of the side growth portion 91 (see
FIGS. 9A and 9B), and thereby affects the flatness within the wafer
surface.
SUMMARY OF THE INVENTION
[0043] The present invention has been devised to solve the
conventionally encountered problems discussed above. It is,
therefore, an object of the present invention to prevent cracks
that develop in a nitride semiconductor growth layer when it is
laid on top of a nitride semiconductor substrate to produce a
nitride semiconductor laser device. It is another object of the
present invention to provide a nitride semiconductor laser device
wherein a nitride semiconductor growth layer is formed with good
surface flatness as a result of a reduced film thickness in a side
growth portion achieved by reducing creep-up growth from a bottom
growth portion of a carved region. It is still another object of
the present invention to provide a method for fabricating such a
nitride semiconductor laser device.
[0044] To achieve the above objects, according to the present
invention, a nitride semiconductor light-emitting device is
provided with: a nitride semiconductor substrate of which at least
part of the surface is formed from a nitride semiconductor; and a
nitride film semiconductor growth layer laid on the surface of the
nitride semiconductor substrate. Here, a low-defect region having a
defect density of 10.sup.6 cm.sup.-2 or less and a carved region in
the shape of a depressed portion are formed on the surface of the
nitride semiconductor substrate. Moreover, the etching angle
.theta., which is the angle between the side face portion of the
depressed portion and an extension line of the bottom face portion
thereof as measured with the depressed portion seen in a sectional
view, is in the range of
75.degree..ltoreq..theta..ltoreq.140.degree..
[0045] In this structure, when the carved region in the shape of a
depression is formed, by adjusting the etching angle of the
sectional shape of the carved region within the range from
75.degree. to 140.degree., it is possible to give it an inverted
tapered shape. In this way, with the nitride semiconductor
light-emitting device of the invention, it is possible to prevent
the development of cracks in the nitride film semiconductor growth
layer. Moreover, it is also possible to reduce the creep-up growth
from the bottom growth portion of the carved region, and thereby to
reduce the film thickness of the side growth portion.
[0046] It is preferable that the etching angle .theta. be
140.degree. or less. The reason is that, with an etching angle
.theta. larger than 140.degree., it is difficult to fabricate the
nitride semiconductor light-emitting device.
[0047] As described above, according to the present invention, when
a nitride semiconductor growth layer is laid on top of a nitride
semiconductor substrate to produce a nitride semiconductor laser
device, a carved region in the shape of a depression is formed on
the nitride semiconductor substrate. The etching angle in the
sectional shape of the carved region is adjusted in the range from
75.degree. to 140.degree., including the range in which the etching
angle forms an inverted tapered shape.
[0048] With this structure, it is possible to prevent the
development of cracks, and also to reduce the creep-up growth from
the bottom growth portion of the carved region. Moreover, it is
possible to reduce the film thickness of the side growth portion,
and thus to form a nitride semiconductor growth layer with good
surface flatness. As a result, it is possible to fabricate the
nitride semiconductor laser device with a high yield.
[0049] This and other objects and features of the present invention
will become clear from the following description, taken in
conjunction with the preferred embodiments with reference to the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0050] FIG. 1A is a schematic sectional view of a nitride
semiconductor laser device embodying the invention;
[0051] FIG. 1B is a top view of FIG. 1A;
[0052] FIG. 2 is a diagram illustrating the film thickness X of the
side growth portion;
[0053] FIG. 3A is a top view of FIG. 3B described below;
[0054] FIG. 3B is a schematic sectional view of the GaN substrate
before the nitride semiconductor layer is grown in the embodiment
of the invention;
[0055] FIG. 4 is a diagram showing the correlation between the
etching angle .theta. and the mean deviation of the p-type layer
thickness;
[0056] FIG. 5 is a diagram showing the correlation between the
layer thickness X of the side growth portion and the mean deviation
of the p-type layer thickness;
[0057] FIG. 6A is a top view of FIG. 6B described below;
[0058] FIG. 6B is a schematic sectional view of a wafer having a
nitride semiconductor growth layer laid on top of a conventional
n-type GaN substrate;
[0059] FIG. 7 is a schematic sectional view of a nitride
semiconductor growth layer;
[0060] FIG. 8 is a graph showing the level difference across the
surface of a wafer having a nitride semiconductor growth layer laid
on top of a conventional n-type GaN substrate;
[0061] FIG. 9A is a diagram illustrating how a top growth portion,
a side growth portion, and a bottom growth portion grow in an
uncarved region, in the side face portion of a carved region, and
in the bottom face portion of the carved region, respectively;
[0062] FIG. 9B is a diagram illustrating how, as the growth of the
semiconductor thin film in the side growth portion progresses, the
growth speed of the semiconductor thin film growing in the top
growth portion is affected to vary; and
[0063] FIG. 10 is a diagram illustrating the growth mode of
creep-up growth.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0064] Hereinafter, embodiments of the present invention will be
described with reference to the accompanying drawings.
[0065] FIG. 1A is a schematic sectional view of a nitride
semiconductor laser device embodying the invention, and FIG. 1B is
a top view of FIG. 1A. FIG. 3B is a schematic sectional view of a
GaN substrate before a nitride semiconductor layer is grown on top
thereof in the embodiment of the invention, and FIG. 3A is a top
view of FIG. 3B. In these diagrams, the surface orientations are
also indicated.
[0066] The nitride semiconductor laser device shown in FIGS. 1A and
1B is produced by laying or otherwise forming a nitride
semiconductor growth layer on top of the GaN substrate shown in
FIGS. 3A and 3B.
[0067] In the following descriptions, a "nitride semiconductor
substrate" is formed from Al.sub.xGa.sub.yIn.sub.zN (where
0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1, 0.ltoreq.z.ltoreq.1, and
x+y+z=1). So long as the nitride semiconductor substrate has a
hexagonal crystal structure, about 10% or less of the nitrogen
contained therein may be substituted with As, P, or Sb. Moreover,
the nitride semiconductor substrate may be doped with Si, O, Cl, S,
C, Ge, Zn, Cd, Mg, or Be. Particularly preferred doping materials
for an n-type nitride semiconductor substrate are Si, O, and
Cl.
[0068] The orientation of the principal plane of the nitride
semiconductor substrate may be aligned with any of a C plane
{0001}, an A plane {11-20}, an R plane {1-102}, an M plane {1-100},
and a {1-101} plane. So long as the principal plane of the
substrate has an off angle less than 2.degree. relative to the
orientation of any of those crystal planes, good surface morphology
is obtained.
[0069] The nitride semiconductor laser device of the embodiment is
produced by growing a nitride semiconductor growth layer 11 on top
of an n-type GaN substrate 10 having carved regions 16, in the
shape of depressed portions, formed on the surface thereof. As
shown in FIGS. 1A and 1B, the carved regions 16 have a sectional
shape such that the width M of the opening of the carved regions 16
is smaller than the width N of the bottom face of the carved
regions 16 (i.e., the carved regions 16 have an inverted tapered
sectional shape).
[0070] Giving the carved regions 16 such a sectional shape helps
reduce "creep-up growth" from a bottom growth portion 19, i.e.,
growth that starts from the bottom face of the carved regions 16.
Doing so also helps reduce the film thickness X (see FIG. 2) of a
side growth portion 18, which is formed by growth starting from the
side faces of the carved regions 16. Consequently, higher evenness
is achieved in the film thickness on a top growth portion 17, which
is formed by growth starting from "uncarved regions," i.e., the
surface of the n-type GaN substrate 10 elsewhere than in the carved
regions 16.
[0071] Now, the definition of the film thickness X of the side
growth portion 18 will be explained with reference to FIG. 2. As
shown in FIG. 2, the film thickness X of the side growth portion 18
is defined as the distance from the end point A of an uncarved
region to the point (the point B in FIG. 2) where the line parallel
to the substrate surface and including the end point A intersects
with the epitaxially grown film. If the film thickness X differs
between both ends of the carved region 16, the thicker value is
taken as the film thickness X.
[0072] In this embodiment, a substrate in which a nitride
semiconductor including low-defect regions is exposed at the
surface thereof is used. It is, however, also possible to use a
substrate that is formed, except at the surface thereof, from
sapphire, SiC, GaAs, Si, or ZnO so long as a nitride semiconductor
growth layer can be laid on top thereof.
[0073] In connection with the nitride semiconductor laser device
described above, first, with reference to the relevant drawings,
how the "n-type GaN substrate before the laying of the nitride
semiconductor growth layer on top thereof" is produced will be
described.
[0074] First, on the entire surface of the n-type GaN substrate 10,
a 1 .mu.m thick layer of SiO.sub.2 or the like is deposited by
sputtering. Subsequently, by a common photolithography process,
photoresist is formed in the [1-100] direction in the shape of
stripes with a width (opening width) of 80 .mu.m and with a period
of 400 .mu.m between adjacent stripes. Next, by RIE (respective ion
etching), the SiO.sub.2 layer and the GaN substrate are etched to
form carved regions 16 with a carving depth Z of 6 .mu.m.
Thereafter, using HF (hydrofluoric acid) as an etchant, the
SiO.sub.2 layer is removed.
[0075] In this way, the n-type GaN substrate 10 before the nitride
semiconductor growth layer is laid on the surface thereof as shown
in FIGS. 3A and 3B is obtained.
[0076] The etching method used to produce the n-type GaN substrate
10 before the laying of the nitride semiconductor growth layer on
top thereof may be dry etching or wet etching.
[0077] When dry etching is used, after the SiO.sub.2 is etched, by
performing wet etching, the carved regions 16 are formed to have an
inverted tapered shape with an etching angle .theta. of 90.degree.
or more. Here, as shown in FIGS. 3A and 3B, the etching angle
.theta. denotes the angle between the side face of the carved
regions 16 and an extension line of the bottom face thereof.
[0078] The solution used in the wet etching here may be a KOH
(potassium hydroxide) solution, a mixed solution of NaOH (sodium
hydroxide) and KOH, or the like. Heating the solution to 80.degree.
C. to 250.degree. C. makes isotropic etching possible, permitting
the carved regions 16 to be formed to have an inverted tapered
shape.
[0079] The n-type GaN substrate 10 used in this embodiment includes
low-defect regions, which have a defect density of about 10.sup.6
cm.sup.-2 or less. The carved regions 16 may be formed after first
growing a thin film of GaN, InGaN, AlGaN, InAlGaN, or the like on
top of the n-type GaN substrate 10 including the low-defect
regions. Moreover, in this embodiment, for example, the etching
angle .theta. may be 100.degree..
[0080] Then, on top of the substrate processed as descried above
(i.e., on top of the n-type GaN substrate 10 before the laying of
the nitride semiconductor growth layer on top thereof), by MOCVD or
the like, a nitride semiconductor growth layer as shown in FIG. 7
is epitaxially grown to produce a nitride semiconductor laser
device as shown in FIGS. 1A and 1B.
[0081] In the nitride semiconductor laser device shown in FIGS. 1A
and 1B, on top of an n-type GaN substrate 10 produced as described
above so as to have a carved region 16 formed thereon, a nitride
semiconductor growth layer 11 having a multiple-layer structure as
shown in FIG. 7 is formed. Moreover, on the surface of the nitride
semiconductor growth layer 11, a laser stripe 12 functioning as a
laser light waveguide (light-emitting portion) is formed, and in
addition an SiO.sub.2 layer 13 for current narrowing is formed so
as to sandwich the laser stripe 12 from both sides.
[0082] Then, over the surfaces of the laser stripe (ridge stripe)
12 and the SiO2 layer 13, a p-type electrode 14 is formed. On the
other hand, on the bottom surface of the n-type GaN substrate 10,
an n-type electrode 15 is formed.
[0083] In the nitride semiconductor growth layer 11, the portion
that is formed by growth from the surface of the n-type GaN
substrate 10 elsewhere than in the carved region 16 is referred to
as the top growth portion 17. The portion formed by growth from the
side faces of the carved region 16 is referred to as the side
growth portion 18. The portion formed by growth from the bottom
face of the carved region 16 is referred to as the bottom growth
portion 19.
[0084] It is preferable that the laser stripe 12 be formed above a
low-defect region included in the n-type GaN substrate 10.
Moreover, for the reason stated later, it is preferable that the
laser stripe 12 not be formed above the carved region 16.
[0085] Using a light interference microscope, a wafer produced by
laying the nitride semiconductor growth layer 11 on top of the
n-type GaN substrate 10 having the carved region 16 formed thereon
so as to have an inverted tapered shape as shown in FIGS. 1A and 1B
was measured. Specifically, the thickness of the Mg-doped p-type
layer was measured using a light interference microscope.
[0086] In this embodiment, the design thickness of the p-type layer
is set at 0.700 .mu.m. Using a light interference microscope, 20
measurements were taken at different places within the wafer
surface, and the mean deviation .sigma. of those measurements were
calculated. As a result, the mean deviation .sigma. of the
thickness of the p-type layer of this wafer was found to be
0.003.
[0087] It is believed that, to satisfactorily reduce the variation
of the characteristics (such as FFP (far-field pattern), threshold
current, and slope) of nitride semiconductor laser devices, the
mean deviation .sigma. needs to be reduced to 0.01 or lower. By
this criterion, the mean deviation .sigma. of the thickness of the
p-type layer of the wafer in question can be said to be
satisfactory, well above the required level.
[0088] For comparison, a nitride semiconductor laser device was
produced in which the laser stripe 12 was formed above the carved
region 16 on the n-type GaN substrate 10 having the nitride
semiconductor growth layer 11 laid on top thereof. Then, in the
same manner as described above, measurements were taken of the
thickness of the p-type layer of the nitride semiconductor laser
device, and the mean deviation .sigma. of those measurements were
calculated.
[0089] It was then found that, in the nitride semiconductor laser
device having the laser stripe 12 located above the carved region
16, the mean deviation .sigma. of the p-type layer was 0.06,
indicating a large variation. This variation in layer thickness
results from forming the laser stripe 12 above the carved region
16.
[0090] The side growth portion 18 causes the semiconductor thin
film to grow from the side faces of the carved region 16 in a
direction approximately perpendicular to those faces. In addition,
creep-up growth from the bottom face of the carved region 16 occurs
in the bottom growth portion 19. As a result, as compared with the
top growth portion 17, the side and bottom growth portions 18 and
19 grow through a more complicated process, making it difficult to
maintain the flatness of the device surface.
[0091] Thus, to reduce the variation of the thickness of the p-type
layer, and to reduce the variation of the characteristics of the
nitride semiconductor laser device, it is preferable that the laser
stripe structure be formed in the top growth portion 17.
[0092] A study was also made of how the position where the laser
stripe 12 is formed affects the nitride semiconductor laser device.
First, as shown in FIG. 1A, let the distance from the center line
of the laser stripe 12 to the end of the carved region 16 be d.
Then, the laser stripe 12 was formed so that the distance d was 20
.mu.m or less. This resulted in large variations in the
characteristics of the nitride semiconductor laser device. This is
because the thickness of the top growth portion 17 at the end
thereof adjoining the carved region 16 is larger than the thickness
of the top growth portion 17 at a central portion thereof,
resulting in the formation of an abnormal growth portion.
[0093] Specifically, if the laser stripe 12 is formed so that the
distance d is 20 .mu.m or less, the abnormal growth portion lies
over a width of about 20 .mu.m from each end of the top growth
portion 17, resulting in large variations in the characteristics of
the nitride semiconductor laser device.
[0094] Thus, it is preferable that the laser stripe 12 be formed in
a region to which the distance from the end of the top growth
portion 17 is 20 .mu.m or more. For example, in this embodiment,
the distance d is set at 40 .mu.m.
[0095] Forming the carved region 16 and then forming the laser
stripe 12 elsewhere than above the carved region 16 as described
above helps greatly reduce the variation of the characteristics of
the nitride semiconductor laser device, and thus helps reduce the
development of cracks in the nitride semiconductor layer. This
leads to dramatically improved yields.
[0096] FIG. 4 shows the relationship between the etching angle
.theta. of the carved region 16 and the mean deviation .sigma. that
indicates the degree of variation of the thickness of the p-type
layer before etching. Here, it is assumed that the layer thickness
of the n-type GaN layer 70 (see FIG. 7) grown on the surface of the
n-type GaN substrate 10 is 2 .mu.m.
[0097] As described earlier, to reduce the variation of the
characteristics of the nitride semiconductor laser device, the mean
deviation .sigma. of the thickness of the p-type layer needs to be
0.01 or less. The graph in FIG. 4 shows that, to meet the
requirement that the mean deviation .sigma. be 0.01 or less, the
etching angle .theta. needs to be 80.degree. or more.
[0098] The graph in FIG. 4 covers a range of etching angles .theta.
up to 110.degree.. In fact, the mean deviation .theta. of the
thickness of the p-type layer was confirmed to be 0.01 or less up
to 140.degree.. With an etching angle .theta. greater than
140.degree., however, it is difficult to produce the nitride
semiconductor laser device. Hence, it is preferable that the
etching angle .theta. be 80.degree. or more but 140.degree. or
less.
[0099] Incidentally, by varying the layer thickness of the n-type
GaN layer 70 (see FIG. 7) grown on the surface of the n-type GaN
substrate 10, it is possible to vary the etching angle that reduces
the creep-up growth of the nitride semiconductor thin film. On the
other hand, GaN is more prone to creep-up growth than AlGaN. This
is because, as compared with AlGaN or the like, GaN is more prone
to migration and thus to lateral growth.
[0100] That is, the greater the layer thickness of the n-type GaN
layer 70 grown on the surface of the n-type GaN substrate 10, the
greater the tendency for creep-up growth, and thus the greater the
thickness of the side growth portion 18. Thus, to reduce this great
tendency for creep-up growth, it is necessary to make the etching
angle .theta. greater.
[0101] Hence, in a case where the layer thickness of the n-type GaN
layer 70 is great, the etching angle .theta. needs to be made
accordingly great. By contrast, in a case where the n-type GaN
layer 70 is not grown on the surface of the n-type GaN substrate 10
(this corresponds to reducing the layer thickness of the n-type GaN
layer 70 to 0 m) but growth is started from the n-type
Al.sub.0.062Ga.sub.0.938N first clad layer 71 (see FIG. 7), even
with a small etching angle .theta., it is possible to reduce
creep-up growth.
[0102] Specifically, as the graph in FIG. 4 shows, in a case where
the layer thickness of the n-type GaN layer 70 is greater than 5
.mu.m, to prevent the variation of the characteristics of the
nitride semiconductor laser device, the mean deviation .sigma. of
the thickness of the p-type layer needs to be 0.01 or less. To
achieve this, the etching angle .theta. needs to be 90.degree. or
more. For the reason stated earlier, it is preferable that the
upper limit of the etching angle .theta. be 140.degree. or
less.
[0103] Moreover, as the graph in FIG. 4 shows, in a case where the
n-type GaN layer 70 is not grown on the surface of the n-type GaN
substrate 10, in which case the layer thickness thereof is 0 .mu.m,
but growth is started from the n-type Al.sub.0.062Ga.sub.0.938N
first clad layer 71 (see FIG. 7), to prevent the variation of the
characteristics of the nitride semiconductor laser device, the mean
deviation .sigma. of the thickness of the p-type layer needs to be
0.01 or less. To achieve this the etching angle .theta. needs to be
75.degree. or more.
[0104] Moreover, for the reason stated earlier, it is preferable
that the upper limit of the etching angle .theta. be 140.degree. or
less. It should be noted that the measurements plotted in the graph
in FIG. 4 were made with the carving depth Z of the carved region
16 set at 6 .mu.m.
[0105] Now, the carving depth Z of the carved region 16 will be
explained. If the carving depth Z is 1 .mu.m or less, the carved
region 16 is almost filled (making it difficult to form a trough),
resulting in the development of cracks. Moreover, the creep-up
growth from the bottom growth portion 19 greatly affects the side
growth portion 18, greatly degrading the flatness. This is
undesirable.
[0106] On the other hand, if the carving depth Z of the carved
region 16 is 30 .mu.m or more, it is extremely difficult to produce
the nitride semiconductor laser device, resulting in lower
repeatability and lower yields. This too is undesirable. Hence, it
is preferable that the carving depth Z of the carved region 16 be
in the range of 1 .mu.m.ltoreq.Z.ltoreq.30 .mu.m.
[0107] FIG. 5 shows the relationship between the thickness of the
side growth portion 18 and the mean deviation .sigma. that
indicates the degree of variation of the thickness of the p-type
layer before the etching for forming the ridge structure. The graph
in FIG. 5 shows that, if the film thickness X of the side growth
portion 18 is greater than 20 .mu.m, the variation of the thickness
of the p-type layer is very large.
[0108] Thus, to obtain satisfactory flatness, and to reduce the
variation of the characteristics of the nitride semiconductor laser
device, it is preferable that the film thickness X of the side
growth portion 18 be 20 .mu.m or less. As described earlier, the
film thickness X of the side growth portion 18 is controlled by
controlling the etching angle .theta. or the film thickness of the
n-type GaN layer 70 or another layer laid beneath.
[0109] In this embodiment, the troughs and ridges shown in FIGS. 1A
and 1B are formed in the shape of stripes that extend in one
direction. It is, however, also possible to form the troughs and
ridges so that they cross one another in a lattice-like (net-like)
pattern.
[0110] The width of the troughs and the width of the ridges may
vary with a fixed period, or may vary in any different manner. The
depth of the troughs may be equal in all of the troughs formed, or
may vary from one trough to the next.
[0111] The nitride semiconductor light-emitting device according to
the invention and the method for fabricating it according to the
invention described above can also be presented in the following
manner.
[0112] In the nitride semiconductor light-emitting device according
to the invention, the etching angle .theta. mentioned above may be
in the range of 85.degree..ltoreq..theta..ltoreq.140.degree.. It is
particularly preferable that, in the nitride film semiconductor
growth layer, the layer that makes contact with the surface of the
nitride semiconductor substrate is a GaN layer, and that the layer
thickness of this GaN layer be 2 .mu.m or more.
[0113] A GaN layer is strongly prone to migration and thus to
lateral growth. This tendency is striking particularly when the
layer thickness of the GaN layer is greater than 2 .mu.m. Thus, to
reduce creep-up growth from the bottom growth portion of a carved
region, and to reduce the film thickness of the side growth portion
of the carved region, the etching angle .theta. needs to be set at
85.degree. or more. The reason that the etching angle .theta. is
140.degree. or less is the same as described earlier.
[0114] In a nitride semiconductor light-emitting device like this,
the layer thickness of the GaN layer mentioned above may be 2 .mu.m
or less.
[0115] As described above, a GaN layer is strongly prone to
migration and thus to lateral growth. However, the smaller the
layer thickness of the GaN layer, the less noticeable the tendency
becomes. Thus, setting the layer thickness of the GaN layer at 2
.mu.m or less is effective in reducing creep-up growth from the
bottom growth portion of the carved region and in reducing the film
thickness of the side growth portion. In this case, it is further
preferable that the etching angle .theta. be set at 80.degree. or
more. The reason that the etching angle .theta. is 140.degree. or
less is the same as described earlier.
[0116] In a nitride semiconductor light-emitting device like this,
in the nitride film semiconductor growth layer mentioned above, the
layer that makes contact with the surface of the nitride
semiconductor substrate may be an AlGaN layer.
[0117] As descried above, a GaN layer is strongly prone to
migration and thus to lateral growth. By contrast, an AlGaN layer
is less prone to migration than a GaN layer.
[0118] Thus, when the layer thickness of the GaN layer is set at 0
.mu.m, and the layer that makes contact with the surface of the
nitride semiconductor substrate is an AlGaN layer, to reduce
creep-up growth from the bottom growth portion of the carved region
and to reduce the film thickness of the side growth portion, it
suffices to set the etching angle .theta. at 75.degree. or more.
The reason that the etching angle .theta. is 140.degree. or less is
the same as described earlier.
[0119] In the nitride semiconductor light-emitting device described
above, the carving depth of the carved region may be 1 .mu.m or
more but 30 .mu.m or less.
[0120] Now, the carving depth of the carved region will be
explained. If the carving depth is 1 .mu.m or less, it is almost
filled, resulting in the development of cracks. Moreover, in this
case, the creep-up growth from the bottom growth portion strongly
affects the side growth portion, greatly degrading the flatness.
This is undesirable.
[0121] On the other hand, if the carving depth of the carved region
is 30 .mu.m or more, it is extremely difficult to produce the
nitride semiconductor light-emitting device, leading to lower
repeatability and lower yields. This too is undesirable. Hence, it
is preferable that the carving depth of the carved region be 1
.mu.m or more but 30 .mu.m or less.
[0122] In the nitride semiconductor light-emitting device described
above, the laser stripe formed as the light-emitting portion in the
nitride semiconductor growth layer may be formed above the
low-defect region elsewhere than above the carved region. In this
case, the laser stripe may be formed 20 .mu.m or more away from the
carved region.
[0123] Forming the laser stripe so that the distance from the
center line of the laser stripe to the carved portion is less than
20 .mu.m results in large variations in the characteristics of the
nitride semiconductor light-emitting device. This is because the
film thickness of the top growth potion at the end thereof
adjoining the carved portion is greater than the thickness of the
top growth portion in a central portion thereof, resulting in the
formation of an abnormal growth portion.
[0124] That is, in a case where an abnormal growth portion lies
over a width of about 20 .mu.m from each end of the top growth
portion, forming the laser stripe in this region results in large
variations in the characteristics of the nitride semiconductor
light-emitting device. Thus, it is preferable that the laser stripe
be formed in a region to which the distance from the end of the top
growth portion is 20 .mu.m or more.
[0125] In the nitride semiconductor light-emitting device described
above, the film thickness of the side growth portion formed as part
of the nitride film semiconductor growth layer on the side faces of
the carved region may be 20 .mu.m or less.
[0126] Giving the side growth portion a film thickness greater than
20 .mu.m results in large variation in the thickness of the p-type
layer. Thus, to obtain satisfactory flatness and to reduce the
variation of the characteristics of the nitride semiconductor
light-emitting device, it is preferable that the film thickness of
the top growth portion be 20 .mu.m or less.
[0127] The present invention also provides a method for fabricating
a nitride semiconductor light-emitting device including, as
described above: a nitride semiconductor substrate of which at
least part of the surface is formed from a nitride semiconductor
and that includes on the surface thereof a low-defect region having
a defect density of 10.sup.6 cm.sup.-2 or less; and a nitride film
semiconductor growth layer formed on the surface of the nitride
semiconductor substrate. The method includes: a first step of
forming a carved region by etching the nitride semiconductor
substrate; and a second step of laying the nitride semiconductor
growth layer on the nitride semiconductor substrate that has
undergone the first step. Here, in the first step, the etching
angle .theta., which is the angle between the side face of a
depressed portion formed as the carved region and the extension
line of the bottom face of the depressed portion, is in the range
of 75.degree..ltoreq..theta..ltore- q.140.degree..
[0128] In the method for fabricating a nitride semiconductor
light-emitting device described above, in the first step, the
etching angle .theta. may be in the range of
85.degree..ltoreq..theta..ltoreq.140- .degree..
[0129] In the method for fabricating a nitride semiconductor
light-emitting device described above, in the second step, the
layer that makes contact with the surface of the nitride
semiconductor substrate may be a 2 .mu.m or less thick GaN
layer.
[0130] In the method for fabricating a nitride semiconductor
light-emitting device described above, in the second step, the
layer that makes contact with the surface of the nitride
semiconductor substrate is an AlGaN layer.
[0131] In the method for fabricating a nitride semiconductor
light-emitting device described above, a laser stripe functioning
as a light-emitting portion may be formed above the low-defect
region, elsewhere than above the carved region. In this case, the
laser stripe may be formed 20 .mu.m or more away from the carved
region.
[0132] In any of the methods for fabricating a nitride
semiconductor light-emitting device described above, the side
growth portion formed, as part of the nitride film semiconductor
growth layer, on the side face of the carved region may be 20 .mu.m
or less thick.
[0133] In any of the methods for fabricating a nitride
semiconductor light-emitting device described above, in the first
step, first a nitride semiconductor layer may be grown on the
nitride semiconductor substrate, with the carved region formed
thereafter.
[0134] Even when first the nitride semiconductor layer is grown
before the carved region is formed, then the carved region is
formed, and then the nitride semiconductor growth layer is laid on
top, the effects of the present invention remain unaffected, making
it possible to provide a nitride semiconductor light-emitting
device wherein a nitride semiconductor growth layer is formed with
good surface flatness.
[0135] The practical examples and embodiments specifically
described hereinbefore are intended merely to clarify the technical
features of the present invention. Accordingly, it should be
understood that the present invention can be practiced in any other
manners than specifically described above, with many variations and
modifications made within the scope of the appended claims.
* * * * *