U.S. patent application number 10/945899 was filed with the patent office on 2005-02-24 for semiconductor device and method for manufacturing the same.
This patent application is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Ueda, Tetsuzo.
Application Number | 20050042788 10/945899 |
Document ID | / |
Family ID | 29229344 |
Filed Date | 2005-02-24 |
United States Patent
Application |
20050042788 |
Kind Code |
A1 |
Ueda, Tetsuzo |
February 24, 2005 |
Semiconductor device and method for manufacturing the same
Abstract
A light emitting layer made of a group III-V nitride
semiconductor is formed between a first semiconductor layer made of
an n-type group III-V nitride semiconductor and a second
semiconductor layer made of a p-type group III-V nitride
semiconductor. In side portions of the second semiconductor layer,
oxidized regions are formed through the oxidization of the second
semiconductor layer itself so as to be spaced apart from each other
in the direction parallel to the plane of the light emitting layer.
A p-side electrode is formed across the entire upper surface of the
second semiconductor layer including the oxidized regions, and an
n-side electrode is formed on one surface of the first
semiconductor layer that is away from the second semiconductor
layer.
Inventors: |
Ueda, Tetsuzo; (Osaka,
JP) |
Correspondence
Address: |
Jack Q. Lever, Jr.
McDERMOTT, WILL & EMERY
600 Thirteenth Street, N.W.
Washington
DC
20005-3096
US
|
Assignee: |
Matsushita Electric Industrial Co.,
Ltd.
Osaka
JP
|
Family ID: |
29229344 |
Appl. No.: |
10/945899 |
Filed: |
September 22, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10945899 |
Sep 22, 2004 |
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10382938 |
Mar 7, 2003 |
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6797532 |
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Current U.S.
Class: |
438/46 |
Current CPC
Class: |
H01S 2304/04 20130101;
H01L 21/02639 20130101; H01S 5/0215 20130101; H01L 33/145 20130101;
H01S 5/2231 20130101; H01L 21/7605 20130101; H01L 21/0262 20130101;
H01S 2304/12 20130101; H01S 5/04254 20190801; H01S 2301/176
20130101; H01S 5/227 20130101; H01S 5/04257 20190801; H01L 21/02532
20130101; H01S 5/0217 20130101; H01S 5/2215 20130101; H01S 5/32341
20130101; H01S 5/0213 20130101; H01S 5/2214 20130101; H01L 21/0254
20130101; H01S 5/2232 20130101; H01L 21/0237 20130101 |
Class at
Publication: |
438/046 |
International
Class: |
H01L 021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 22, 2002 |
JP |
2002-080229 |
Claims
1. A semiconductor device, comprising a first semiconductor layer
of a first conductivity type and a second semiconductor layer of a
second conductivity type, including an active region, wherein at
least one of the first semiconductor layer and the second
semiconductor layer includes oxidized regions, which are spaced
apart from each other in a direction parallel to a plane of the
active region and are obtained through oxidization of the at least
one of the first semiconductor layer and the second semiconductor
layer itself.
2. The semiconductor device of claim 1, further comprising: a first
ohmic electrode formed on the second semiconductor layer; and a
second ohmic electrode formed on one side of the first
semiconductor layer that is away from the second semiconductor
layer.
3. The semiconductor device of claim 2, wherein a conductive
substrate is provided between the first semiconductor layer and the
second ohmic electrode.
4. The semiconductor device of claim 3, wherein the conductive
substrate is made of silicon carbide, silicon, gallium arsenide,
gallium phosphide, indium phosphide, zinc oxide or a metal.
5. The semiconductor device of claim 1, wherein the first
semiconductor layer and the second semiconductor layer are formed
in this order on an insulative substrate, the semiconductor device
further comprising: a first ohmic electrode formed on the second
semiconductor layer; and a second ohmic electrode formed on an
exposed portion of one surface of the first semiconductor layer
that is closer to the second semiconductor layer.
6. The semiconductor device of claim 5, wherein the insulative
substrate is made of sapphire, magnesium oxide or lithium gallium
aluminum oxide (LiGa.sub.xAl.sub.1-xO.sub.2 (where
0.ltoreq.x.ltoreq.1)).
7. The semiconductor device of claim 1, wherein the oxidized
regions are formed so as to include the active region.
8. The semiconductor device of claim 1, wherein at least one of the
first semiconductor layer and the second semiconductor layer
includes a current constriction section formed by removing side
portions of the at least one of the first semiconductor layer and
the second semiconductor layer.
9. The semiconductor device of claim 8, wherein a ridge portion to
be a waveguide is formed in an upper portion of the current
constriction section.
10. The semiconductor device of claim 1, wherein an insulating film
is formed on the oxidized regions.
11. The semiconductor device of claim 10, wherein the insulating
film is made of silicon oxide or silicon nitride.
12. The semiconductor device of claim 1, wherein the first
semiconductor layer and the second semiconductor layer are made of
a compound semiconductor containing nitrogen.
13. A method for manufacturing a semiconductor device, comprising:
a first step of forming a first semiconductor layer of a first
conductivity type; a second step of forming a second semiconductor
layer of a second conductivity type on the first semiconductor
layer, thereby forming an active region between the first
semiconductor layer and the second semiconductor layer, and a third
step of selectively oxidizing at least the second semiconductor
layer, thereby forming, at least in the second semiconductor layer,
oxidized regions spaced apart from each other in a direction
parallel to a plane of the active region.
14. The method for manufacturing a semiconductor device of claim
13, wherein the third step includes a step of selectively covering
an upper surface of the second semiconductor layer by a mask film
made of a material that is less likely to be oxidized than the
second semiconductor layer.
15. The method for manufacturing a semiconductor device of claim
14, further comprising, after the third step, a fourth step of
forming an ohmic electrode on the second semiconductor layer after
removing the mask film.
16. The method for manufacturing a semiconductor device of claim
13, further comprising, after the third step: a fourth step of
forming a first ohmic electrode on the second semiconductor layer;
and a fifth step of forming a second ohmic electrode on one surface
of the first semiconductor layer that is away from the active
region.
17. The method for manufacturing a semiconductor device of claim
16, wherein the fourth step includes: a step of forming an
insulating film on the second semiconductor layer including the
oxidized regions; a step of forming a resist pattern having an
opening corresponding to a portion of the insulating film above the
second semiconductor layer, and then etching the insulating film
while using the formed resist pattern as a mask, thereby
transferring an opening pattern onto the insulating film; and a
step of depositing a metal film on the second semiconductor layer
including the resist pattern, and lifting off the resist pattern,
thereby forming the first ohmic electrode from the metal film.
18. The method for manufacturing a semiconductor device of claim
17, wherein the insulating film is made of silicon oxide or silicon
nitride.
19. The method for manufacturing a semiconductor device of claim
13, further comprising, after the third step: a fourth step of
forming a first ohmic electrode on the second semiconductor layer;
and a fifth step of selectively removing the active region and the
second semiconductor layer, thereby forming an exposed region of
the first semiconductor layer, and forming a second ohmic electrode
on the formed exposed region.
20. The method for manufacturing a semiconductor device of claim
19, wherein the fourth step includes: a step of forming an
insulating film on the second semiconductor layer including the
oxidized regions; a step of forming a resist pattern having an
opening corresponding to a portion of the insulating film above the
second semiconductor layer, and then etching the insulating film
while using the formed resist pattern as a mask, thereby
transferring an opening pattern onto the insulating film; and a
step of depositing a metal film on the second semiconductor layer
including the resist pattern, and lifting off the resist pattern,
thereby forming the first ohmic electrode from the metal film.
21. The method for manufacturing a semiconductor device of claim
20, wherein the insulating film is made of silicon oxide or silicon
nitride.
22. The method for manufacturing a semiconductor device of claim
13, wherein: in the first step, the first semiconductor layer is
formed on a substrate; and the method further comprises, after the
third step, a step of separating the substrate from the first
semiconductor layer.
23. The method for manufacturing a semiconductor device of claim
22, wherein the substrate is made of sapphire, silicon carbide,
silicon, gallium arsenide, gallium phosphide, indium phosphide,
magnesium oxide, zinc oxide or lithium gallium aluminum oxide
(LiGa.sub.xAl.sub.1-xO.sub.2 (where 0.ltoreq.x.ltoreq.1)).
24. The method for manufacturing a semiconductor device of claim
22, wherein the substrate separation step includes a step of
bonding a support substrate for supporting the second semiconductor
layer to an upper surface of the second semiconductor layer.
25. The method for manufacturing a semiconductor device of claim
24, further comprising, after the substrate separation step, a step
of forming an ohmic electrode on the support substrate.
26. The method for manufacturing a semiconductor device of claim
24, wherein the support substrate is made of silicon, gallium
arsenide, gallium phosphide, indium phosphide or a metal.
27. The method for manufacturing a semiconductor device of claim
22, wherein the substrate separation step is performed by a
polishing method.
28. The method for manufacturing a semiconductor device of claim
22, wherein: the substrate is made of a material whose forbidden
band width is larger than that of the first semiconductor layer;
the substrate separation step includes a step of irradiating the
first semiconductor layer with irradiation light from one surface
of the substrate that is away from the first semiconductor layer;
and an energy of the irradiation light is smaller than the
forbidden band width of the substrate and larger than that of the
first semiconductor layer.
29. The method for manufacturing a semiconductor device of claim
28, wherein the irradiation light is laser light that oscillates in
a pulsed manner.
30. The method for manufacturing a semiconductor device of claim
28, wherein the irradiation light is an emission line of a mercury
lamp.
31. The method for manufacturing a semiconductor device of claim
28, wherein the substrate separation step includes a step of
heating the substrate.
32. The method for manufacturing a semiconductor device of claim
28, wherein in the substrate separation step, the irradiation light
is radiated so as to scan a surface of the substrate.
33. The method for manufacturing a semiconductor device of claim
22, wherein: the first semiconductor layer is made of a plurality
of semiconductor layers having different compositions; the
substrate is made of a material whose forbidden band width is
larger than a forbidden band width of one of the plurality of
semiconductor layers that has a smallest forbidden band width; the
substrate separation step includes a step of irradiating the first
semiconductor layer with irradiation light from one surface of the
substrate that is away from the first semiconductor layer; and an
energy of the irradiation light is smaller than the forbidden band
width of the substrate and larger than the forbidden band width of
one of the plurality of semiconductor layers that has the smallest
forbidden band width.
34. The method for manufacturing a semiconductor device of claim
33, wherein the irradiation light is laser light that oscillates in
a pulsed manner.
35. The method for manufacturing a semiconductor device of claim
33, wherein the irradiation light is an emission line of a mercury
lamp.
36. The method for manufacturing a semiconductor device of claim
33, wherein the substrate separation step includes a step of
heating the substrate.
37. The method for manufacturing a semiconductor device of claim
33, wherein in the substrate separation step, the irradiation light
is radiated so as to scan a surface of the substrate.
38. The method for manufacturing a semiconductor device of claim
13, further comprising, between the second step and the third step,
a fourth step of etching at least the second semiconductor layer,
thereby forming a current constriction section having a convex
cross section at least in the second semiconductor layer.
39. The method for manufacturing a semiconductor device of claim
38, wherein in the fourth step, the current constriction section is
formed so as to reach the first semiconductor layer.
40. The method for manufacturing a semiconductor device of claim
38, wherein in the fourth step, the current constriction section is
formed so as not to reach the active region.
41. The method for manufacturing a semiconductor device of claim
38, wherein the fourth step includes a step of forming a ridge
portion to be a waveguide in an upper portion of the second
semiconductor layer within the current constriction section.
42. The method for manufacturing a semiconductor device of claim
13, wherein in the third step, the oxidization is performed in an
atmosphere containing an oxygen gas or water vapor.
43. The method for manufacturing a semiconductor device of claim
13, wherein the first semiconductor layer and the second
semiconductor layer are deposited by using one of a metal organic
chemical vapor deposition method, a molecular beam epitaxy method
and a hydride vapor phase epitaxy method, or by using more than one
of the methods in combination.
44. The method for manufacturing a semiconductor device of claim
13, wherein the first semiconductor layer and the second
semiconductor layer are made of a compound semiconductor containing
nitrogen.
45-67. (Cancelled)
68. A method for manufacturing a semiconductor device, comprising:
a first step of forming a first semiconductor layer of a first
conductivity type; a second step of forming a portion of a second
semiconductor layer of a second conductivity type on the first
semiconductor layer, thereby forming an active region between the
first semiconductor layer and the second semiconductor layer, a
third step of selectively oxidizing the first semiconductor layer,
the active region and the portion of the second semiconductor
layer, thereby forming oxidized regions spaced apart from each
other in a direction parallel to a plane of the second
semiconductor layer, in the first semiconductor layer, the active
region and the portion of the second semiconductor layer; and a
fourth step of forming a rest of the second semiconductor layer on
the portion of the second semiconductor layer including the
oxidized regions.
69. The method for manufacturing a semiconductor device of claim
68, wherein in the third step, the oxidization is performed in an
atmosphere containing an oxygen gas or water vapor.
70. The method for manufacturing a semiconductor device of claim
68, wherein the first semiconductor layer and the second
semiconductor layer are deposited by using one of a metal organic
chemical vapor deposition method, a molecular beam epitaxy method
and a hydride vapor phase epitaxy method, or by using more than one
of the methods in combination.
71. The method for manufacturing a semiconductor device of claim
68, wherein the first semiconductor layer and the second
semiconductor layer are made of a compound semiconductor containing
nitrogen.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a semiconductor device such
as a short-wavelength light emitting diode device or a
short-wavelength semiconductor laser device, and a method for
manufacturing the same.
[0002] A semiconductor material made of a group III-V nitride
semiconductor, having a wide forbidden band, can be used in light
emitting devices, specifically, light emitting diode devices and
short-wavelength semiconductor laser devices that are capable of
emitting light of a color in a visible region such as blue, green
or white. Among others, light emitting diode devices have already
been in practical use in large-size display apparatuses, traffic
signals, etc. Particularly, white light emitting diode devices,
which give white light by exciting a fluorescent substance, are
expected to replace conventional lighting fixtures such as electric
bulbs and fluorescent lamps. Moreover, the development of
semiconductor laser devices has reached a point where samples are
being shipped and products are being manufactured although in small
quantities, for use in high-density, large-capacity optical disk
apparatuses using blue-violet laser light.
[0003] The crystal growth of a group III-V nitride semiconductor,
or a so-called "gallium nitride (GaN) semiconductor", has been
difficult, as is also the case with other wide gap semiconductors.
However, with the recent significant improvements in crystal growth
techniques such as a metal organic chemical vapor deposition
method, light emitting diode devices capable of emitting light of
short wavelengths such as blue light have already been in practical
use.
[0004] Moreover, since a substrate made of gallium nitride is
difficult to produce, a gallium nitride semiconductor cannot be
grown by a crystal growth technique that is used with silicon (Si)
or gallium arsenide (GaAs), i.e., growing a semiconductor layer
(epitaxial growth layer) on a substrate having the same composition
as that of the semiconductor layer. Therefore, a so-called
"heteroepitaxial growth process" is typically employed, in which
the epitaxial growth layer is grown on a substrate having a
different composition from that of the epitaxial growth layer,
e.g., a sapphire substrate.
[0005] As a result, a gallium nitride semiconductor layer grown on
a sapphire substrate is currently exhibiting the most desirable
device characteristics, where the crystal defect density of the
epitaxial growth layer is about 1.times.10.sup.7 cm.sup.-2.
However, since sapphire is insulative, in order to form a device
including a p-n junction on a substrate made of sapphire, it is
necessary to selectively remove the p-type semiconductor layer or
the n-type semiconductor layer after the epitaxial growth and to
form a p-type electrode and an n-type electrode on the principal
surface of the substrate.
[0006] Moreover, since it is typically difficult to perform a wet
etching process with an acidic solution, or the like, on a nitride
semiconductor, a dry etching method such as reactive ion etching is
normally used in such a selective removal step.
First Conventional Example
[0007] A method for manufacturing a semiconductor device according
to a first conventional example will now be described with
reference to the drawings.
[0008] FIG. 21 is a cross-sectional view illustrating a light
emitting diode device, which is a semiconductor device of the first
conventional example.
[0009] As illustrated in FIG. 21, first, a buffer layer (not shown)
made of gallium nitride or aluminum nitride, an n-type cladding
layer 102 made of n-type aluminum gallium nitride, an active layer
103 including a quantum well structure made of undoped indium
gallium nitride, and a p-type cladding layer 104 made of p-type
aluminum gallium nitride are grown in this order on a substrate 101
made of sapphire by a metal organic chemical vapor deposition
method, or the like, to form an epitaxial layer. As a current is
externally injected into the n-type cladding layer 102 and the
p-type cladding layer 104, electrons and holes are confined in the
active layer 103, and output light is produced through
recombination of electrons and holes.
[0010] Then, the p-type cladding layer 104, the active layer 103
and an upper portion of the n-type cladding layer 102 are
selectively etched by a reactive ion etching method to form a
current constriction section 200 in the epitaxial layer. Then, the
p-side electrode 105 is formed on the p-type cladding layer 104 in
the current constriction section 200, and an n-side electrode 106
is formed on the exposed region of the n-type cladding layer
102.
Second Conventional Example
[0011] FIG. 22 is a cross-sectional view illustrating a
semiconductor laser device, which is a semiconductor device of the
second conventional example.
[0012] As illustrated in FIG. 22, in order to produce a
semiconductor laser device, an upper portion of the current
constriction section 200 is again subjected to a reactive ion
etching method to form a ridge portion 201 to be a waveguide, and
then the p-side electrode 105 is formed in a stripe pattern.
Furthermore, the structure is cleaved along a plane perpendicular
to the direction in which the p-side electrode 105 having a stripe
pattern extends, thereby forming a cavity with the two opposing
cleaved surfaces being mirrors. Herein, the upper surface excluding
the p-side electrode 105 and the n-side electrode 106 is covered by
an insulating film 107 made of silicon oxide.
[0013] However, with the methods for manufacturing a semiconductor
device of the first and second conventional examples, a nitride
semiconductor layer for forming the current constriction section
200 needs to be subjected to a dry etching process. The dry etching
process damages the side surfaces of the current constriction
section 200. With such a damage, when a current is supplied through
the semiconductor device, a leakage current occurs through the
damaged portions, thereby increasing the operating current of a
light emitting diode device, or the threshold current value of a
semiconductor laser device.
[0014] Moreover, as described above, sapphire, which is insulative,
is used for the substrate 101, whereby both of the p-side electrode
105 and the n-side electrode 106 need to be formed on the principal
surface of the substrate 101. This increases the series resistance
value as a p-n junction, while increasing the device cost because
of an increase in the chip area.
[0015] Moreover, sapphire has a relatively small thermal
conductivity, and thus a poor heat radiating property. Therefore,
when a semiconductor laser device, for example, is produced using
sapphire, it is difficult to increase the operating lifetime of the
semiconductor laser device.
SUMMARY OF THE INVENTION
[0016] In view of these problems in the prior art, a first object
of the present invention is to provide a semiconductor device using
a group III-V nitride semiconductor, in which a current
constriction section can be formed without damaging an exposed
surface (side surface) of an active region. Moreover, a second
object of the present invention is to reduce the series resistance
value and improve the heat radiating property.
[0017] In order to achieve the first object, the present invention
employs a structure in which a semiconductor layer including an
active region is oxidized at positions spaced apart from each other
to form oxidized regions so that the oxidized regions form a
current constriction section. Moreover, even when the semiconductor
layer is dry-etched, the side surface of the current constriction
section is oxidized.
[0018] Moreover, in order to achieve the second object in addition
to the first object, a semiconductor layer is formed on a substrate
so that an active region is included in the semiconductor layer,
after which the substrate is removed from the semiconductor
layer.
[0019] Specifically, a semiconductor device of the present
invention, which achieves the first object, includes a first
semiconductor layer of a first conductivity type and a second
semiconductor layer of a second conductivity type, including an
active region, wherein at least one of the first semiconductor
layer and the second semiconductor layer includes oxidized regions,
which are spaced apart from each other in a direction parallel to a
plane of the active region and are obtained through oxidization of
the at least one of the first semiconductor layer and the second
semiconductor layer itself
[0020] With the semiconductor device of the present invention, the
oxidized regions are formed so as to be spaced apart from each
other in the direction parallel to the plane of the active region,
whereby the oxidized regions function as a current constriction
structure. Furthermore, the oxidized regions are obtained through
oxidization of the first semiconductor layer or the second
semiconductor layer itself, whereby it is not necessary to use a
dry etching process for the current constriction structure, thus
preventing the current constriction structure from being damaged.
As a result, it is possible to prevent a leakage current occurring
in the active region via a damaged portion.
[0021] It is preferred that the semiconductor device of the present
invention further includes: a first ohmic electrode formed on the
second semiconductor layer; and a second ohmic electrode formed on
one side of the first semiconductor layer that is away from the
second semiconductor layer. In this way, the second object is
achieved.
[0022] In the semiconductor device of the present invention, it is
preferred that a conductive substrate is provided between the first
semiconductor layer and the second ohmic electrode.
[0023] In such a case, it is preferred that the conductive
substrate is made of silicon carbide, silicon, gallium arsenide,
gallium phosphide, indium phosphide, zinc oxide or a metal.
[0024] In the semiconductor device of the present invention, it is
preferred that the first semiconductor layer and the second
semiconductor layer are formed in this order on an insulative
substrate, the semiconductor device further including: a first
ohmic electrode formed on the second semiconductor layer; and a
second ohmic electrode formed on an exposed portion of one surface
of the first semiconductor layer that is closer to the second
semiconductor layer.
[0025] In such a case, it is preferred that the insulative
substrate is made of sapphire, magnesium oxide or lithium gallium
aluminum oxide (LiGa.sub.xAl.sub.1-xO.sub.2 (where
0.ltoreq.x.ltoreq.1)).
[0026] In the semiconductor device of the present invention, it is
preferred that the oxidized regions are formed so as to include the
active region.
[0027] In the semiconductor device of the present invention, it is
preferred that at least one of the first semiconductor layer and
the second semiconductor layer includes a current constriction
section formed by removing side portions of the at least one of the
first semiconductor layer and the second semiconductor layer.
[0028] In such a case, it is preferred that a ridge portion to be a
waveguide is formed in an upper portion of the current constriction
section.
[0029] In the semiconductor device of the present invention, it is
preferred that an insulating film is formed on the oxidized
regions.
[0030] In such a case, it is preferred that the insulating film is
made of silicon oxide or silicon nitride.
[0031] In the semiconductor device of the present invention, it is
preferred that the first semiconductor layer and the second
semiconductor layer are made of a compound semiconductor containing
nitrogen.
[0032] A first method for manufacturing a semiconductor device of
the present invention, which achieves the first object, includes: a
first step of forming a first semiconductor layer of a first
conductivity type; a second step of forming a second semiconductor
layer of a second conductivity type on the first semiconductor
layer, thereby forming an active region between the first
semiconductor layer and the second semiconductor layer; and a third
step of selectively oxidizing at least the second semiconductor
layer, thereby forming, at least in the second semiconductor layer,
oxidized regions spaced apart from each other in a direction
parallel to a plane of the active region.
[0033] With the first method for manufacturing a semiconductor
device, the oxidized regions are formed so as to be spaced apart
from each other in the direction parallel to the plane of the
active region, whereby the oxidized regions function as a current
constriction section. In addition, the oxidized regions are
obtained through oxidization of the second semiconductor layer
itself, whereby it is not necessary to use a dry etching process
for forming the current constriction section, thus preventing an
etching damage to the current constriction section. As a result, it
is possible to prevent a leakage current occurring in the active
region via a damaged portion.
[0034] In the first method for manufacturing a semiconductor
device, it is preferred that the third step includes a step of
selectively covering an upper surface of the second semiconductor
layer by a mask film made of a material that is less likely to be
oxidized than the second semiconductor layer.
[0035] In such a case, it is preferred that the first method for
manufacturing a semiconductor device further includes, after the
third step, a fourth step of forming an ohmic electrode on the
second semiconductor layer after removing the mask film.
[0036] It is preferred that the first method for manufacturing a
semiconductor device further includes, after the third step: a
fourth step of forming a first ohmic electrode on the second
semiconductor layer; and a fifth step of forming a second ohmic
electrode on one surface of the first semiconductor layer that is
away from the active region. In this way, the second object is
achieved.
[0037] It is preferred that the first method for manufacturing a
semiconductor device further includes, after the third step: a
fourth step of forming a first ohmic electrode on the second
semiconductor layer; and a fifth step of selectively removing the
active region and the second semiconductor layer, thereby forming
an exposed region of the first semiconductor layer, and forming a
second ohmic electrode on the formed exposed region.
[0038] In such a case, it is preferred that the fourth step
includes: a step of forming an insulating film on the second
semiconductor layer including the oxidized regions; a step of
forming a resist pattern having an opening corresponding to a
portion of the insulating film above the second semiconductor
layer, and then etching the insulating film while using the formed
resist pattern as a mask, thereby transferring an opening pattern
onto the insulating film; and a step of depositing a metal film on
the second semiconductor layer including the resist pattern, and
lifting off the resist pattern, thereby forming the first ohmic
electrode from the metal film.
[0039] In the first method for manufacturing a semiconductor
device, it is preferred that the insulating film is made of silicon
oxide or silicon nitride.
[0040] In the first method for manufacturing a semiconductor
device, it is preferred that in the first step, the first
semiconductor layer is formed on a substrate; and the method
further includes, after the third step, a step of separating the
substrate from the first semiconductor layer. In this way, the
second object is achieved.
[0041] In such a case, it is preferred that the first method for
manufacturing a semiconductor device further includes, between the
second step and the third step, a fourth step of etching at least
the second semiconductor layer, thereby forming a current
constriction section having a convex cross section at least in the
second semiconductor layer.
[0042] Moreover, in such a case, it is preferred that in the fourth
step, the current constriction section is formed so as to reach the
first semiconductor layer.
[0043] Alternatively, in such a case, it is preferred that in the
fourth step, the current constriction section is formed so as not
to reach the active region.
[0044] Moreover, in such a case, it is preferred that the fourth
step includes a step of forming a ridge portion to be a waveguide
in an upper portion of the second semiconductor layer within the
current constriction section.
[0045] In the first method for manufacturing a semiconductor
device, it is preferred that in the third step, the oxidization is
performed in an atmosphere containing an oxygen gas or water
vapor.
[0046] A second method for manufacturing a semiconductor device of
the present invention includes: a first step of forming a portion
of a first semiconductor layer of a first conductivity type; a
second step of selectively oxidizing the portion of the first
semiconductor layer, thereby forming, in the portion of the first
semiconductor layer, oxidized regions spaced apart from each other
in a direction parallel to a plane of the first semiconductor
layer; a third step of forming a rest of the first semiconductor
layer on the portion of the first semiconductor layer including the
oxidized regions; and a fourth step of forming a second
semiconductor layer of a second conductivity type on: the first
semiconductor layer, thereby forming an active region between the
first semiconductor layer and the second semiconductor layer.
[0047] With the second method for manufacturing a semiconductor
device, the oxidized regions to be the current constriction section
are formed in a portion of the first semiconductor layer, and then
the rest of the first semiconductor layer, the active region and
the second semiconductor layer are formed. Therefore, as with the
first method for manufacturing a semiconductor device, it is not
necessary to use a dry etching process for forming the current
constriction section, thus preventing an etching damage to the
current constriction section. As a result, it is possible to
prevent a leakage current occurring in the active region via a
damaged portion.
[0048] In the second method for manufacturing a semiconductor
device, it is preferred that the second step includes a step of
selectively covering an upper surface of the portion of the first
semiconductor layer by a mask film made of a material that is less
likely to be oxidized than the first semiconductor layer.
[0049] In such a case, it is preferred that the second method for
manufacturing a semiconductor device further includes: a fifth step
of removing the mask film, between the second step and the third
step; and a sixth step of forming an ohmic electrode on the second
semiconductor layer, after the fourth step.
[0050] It is preferred that the second method for manufacturing a
semiconductor device further includes, after the fourth step: a
fifth step of forming a first ohmic electrode on the second
semiconductor layer; and a sixth step of forming a second ohmic
electrode on one surface of the first semiconductor layer that is
away from the active region.
[0051] In the second method for manufacturing a semiconductor
device, it is preferred that in the first step, the portion of the
first semiconductor layer is formed on a substrate; and the method
further includes, after the fourth step, a step of separating the
substrate from the first semiconductor layer. In this way, the
second object is achieved.
[0052] In the second method for manufacturing a semiconductor
device, it is preferred that in the second step, the oxidization is
performed in an atmosphere containing an oxygen gas or water
vapor.
[0053] A third method for manufacturing a semiconductor device of
the present invention includes: a first step of forming a first
semiconductor layer of a first conductivity type; a second step of
forming a portion of a second semiconductor layer of a second
conductivity type on the first semiconductor layer, thereby forming
an active region between the first semiconductor layer and the
second semiconductor layer; a third step of selectively oxidizing
the first semiconductor layer, the active region and the portion of
the second semiconductor layer, thereby forming oxidized regions
spaced apart from each other in a direction parallel to a plane of
the second semiconductor layer, in the first semiconductor layer,
the active region and the portion of the second semiconductor
layer; and a fourth step of forming a rest of the second
semiconductor layer on the portion of the second semiconductor
layer including the oxidized regions.
[0054] With the third method for manufacturing a semiconductor
device, the oxidized regions to be the current constriction section
are formed in the first semiconductor layer, the active region and
a portion of the second semiconductor layer, and then the rest of
the second semiconductor layer is formed. Therefore, as with the
second method for manufacturing a semiconductor device, it is not
necessary to use a dry etching process for forming the current
constriction section, thus preventing an etching damage to the
current constriction section. As a result, it is possible to
prevent a leakage current occurring in the active region via a
damaged portion.
[0055] In the third method for manufacturing a semiconductor
device, it is preferred that in the third step, the oxidization is
performed in an atmosphere containing an oxygen gas or water
vapor.
[0056] In the first or second method for manufacturing a
semiconductor device, it is preferred that the substrate is made of
sapphire, silicon carbide, silicon, gallium arsenide, gallium
phosphide, indium phosphide, magnesium oxide, zinc oxide or lithium
gallium aluminum oxide (LiGa.sub.xAl.sub.1-xO.sub.2 (where
0.ltoreq.x.ltoreq.1)).
[0057] In the first or second method for manufacturing a
semiconductor device, it is preferred that the substrate separation
step includes a step of bonding a support substrate for supporting
the second semiconductor layer to an upper surface of the second
semiconductor layer.
[0058] In such a case, it is preferred that the first or second
method for manufacturing a semiconductor device further includes,
after the substrate separation step, a step of forming an ohmic
electrode on the support substrate.
[0059] In such a case, it is preferred that the support substrate
is made of silicon, gallium arsenide, gallium phosphide, indium
phosphide or a metal.
[0060] In the first or second method for manufacturing a
semiconductor device, it is preferred that the substrate separation
step is performed by a polishing method.
[0061] In the first or second method for manufacturing a
semiconductor device, it is preferred that the substrate is made of
a material whose forbidden band width is larger than that of the
first semiconductor layer; the substrate separation step includes a
step of irradiating the first semiconductor layer with irradiation
light from one surface of the substrate that is away from the first
semiconductor layer; and an energy of the irradiation light is
smaller than the forbidden band width of the substrate and larger
than that of the first semiconductor layer.
[0062] Moreover, in the first or second method for manufacturing a
semiconductor device, it is preferred that the first semiconductor
layer is made of a plurality of semiconductor layers having
different compositions; the substrate is made of a material whose
forbidden band width is larger than a forbidden band width of one
of the plurality of semiconductor layers that has a smallest
forbidden band width; the substrate separation step includes a step
of irradiating the first semiconductor layer with irradiation light
from one surface of the substrate that is away from the first
semiconductor layer; and an energy of the irradiation light is
smaller than the forbidden band width of the substrate and larger
than the forbidden band width of one of the plurality of
semiconductor layers that has the smallest forbidden band
width.
[0063] In such cases, it is preferred that the irradiation light is
laser light that oscillates in a pulsed manner.
[0064] Alternatively, it is preferred that the irradiation light is
an emission line of a mercury lamp.
[0065] Moreover, in such a case, it is preferred that the substrate
separation step includes a step of heating the substrate.
[0066] In the first or second method for manufacturing a
semiconductor device, it is preferred that in the substrate
separation step, the irradiation light is radiated so as to scan a
surface of the substrate.
[0067] In the first to third methods for manufacturing a
semiconductor device, it is preferred that the first semiconductor
layer and the second semiconductor layer are deposited by using one
of a metal organic chemical vapor deposition method, a molecular
beam epitaxy method and a hydride vapor phase epitaxy method, or by
using more than one of the methods in combination.
[0068] In the first to third methods for manufacturing a
semiconductor device, it is preferred that the first semiconductor
layer and the second semiconductor layer are made of a compound
semiconductor containing nitrogen.
BRIEF DESCRIPTION OF THE DRAWINGS
[0069] FIG. 1 is a cross-sectional view illustrating a
semiconductor device according to a first embodiment of the present
invention.
[0070] FIG. 2A to FIG. 2E are cross-sectional views sequentially
illustrating steps in a first method for manufacturing a
semiconductor device according to the first embodiment of the
present invention.
[0071] FIG. 3A to FIG. 3E are cross-sectional views sequentially
illustrating steps in a second method for manufacturing a
semiconductor device according to the first embodiment of the
present invention.
[0072] FIG. 4A to FIG. 4C are cross-sectional views sequentially
illustrating steps in a method for manufacturing a semiconductor
device according to a first variation of the first embodiment of
the present invention.
[0073] FIG. 5 is a cross-sectional view illustrating a
semiconductor device according to a second variation of the first
embodiment of the present invention.
[0074] FIG. 6 is a cross-sectional view illustrating a
semiconductor device according to a second embodiment of the
present invention.
[0075] FIG. 7A to FIG. 7D are cross-sectional views sequentially
illustrating steps in a method for manufacturing a semiconductor
device according to the second embodiment of the present
invention.
[0076] FIG. 8 is a cross-sectional view illustrating a
semiconductor device according to a third embodiment of the present
invention.
[0077] FIG. 9A to FIG. 9D are cross-sectional views sequentially
illustrating steps in a method for manufacturing a semiconductor
device according to the third embodiment of the present
invention.
[0078] FIG. 10A to FIG. 10D are cross-sectional views sequentially
illustrating steps in a method for manufacturing a semiconductor
device according to the third embodiment of the present
invention.
[0079] FIG. 11 is a cross-sectional view illustrating a
semiconductor device according to a fourth embodiment of the
present invention.
[0080] FIG. 12 is a cross-sectional view illustrating a
semiconductor device according to a fifth embodiment of the present
invention.
[0081] FIG. 13A to FIG. 13D are cross-sectional views sequentially
illustrating steps in a method for manufacturing a semiconductor
device according to the fifth embodiment of the present
invention.
[0082] FIG. 14A to FIG. 14D are cross-sectional views sequentially
illustrating steps in the method for manufacturing a semiconductor
device according to the fifth embodiment of the present
invention.
[0083] FIG. 15 is a cross-sectional view illustrating a
semiconductor device according to a sixth embodiment of the present
invention.
[0084] FIG. 16A to FIG. 16D are cross-sectional views sequentially
illustrating steps in a method for manufacturing a semiconductor
device according to the sixth embodiment of the present
invention.
[0085] FIG. 17A to FIG. 17C are cross-sectional views sequentially
illustrating steps in the method for manufacturing a semiconductor
device according to the sixth embodiment of the present
invention.
[0086] FIG. 18 is a cross-sectional view illustrating a
semiconductor device according to a seventh embodiment of the
present invention.
[0087] FIG. 19A to FIG. 19D are cross-sectional views sequentially
illustrating steps in a method for manufacturing a semiconductor
device according to the seventh embodiment of the present
invention.
[0088] FIG. 20A to FIG. 20C are cross-sectional views sequentially
illustrating steps in the method for manufacturing a semiconductor
device according to the seventh embodiment of the present
invention.
[0089] FIG. 21 is a cross-sectional view illustrating a light
emitting diode device according to a first conventional
example.
[0090] FIG. 22 is a cross-sectional view illustrating a
semiconductor laser device according to a second conventional
example.
DETAILED DESCRIPTION OF THE INVENTION
First Embodiment
[0091] The first embodiment of the present invention will now be
described with reference to the drawings.
[0092] FIG. 1 is a cross-sectional view illustrating, as a
semiconductor device according to the first embodiment of the
present invention, a semiconductor light emitting device that can
be applied to a light emitting diode device or a semiconductor
laser device.
[0093] As illustrated in FIG. 1, a light emitting layer 12 as an
active region made of a group III-V nitride semiconductor is formed
between a first semiconductor layer 11 made of an n-type group
III-V nitride semiconductor and a second semiconductor layer 13
made of a p-type group Ill-V nitride semiconductor.
[0094] In the opposing side portions of the second semiconductor
layer 13, oxidized regions 13a, which are spaced apart from each
other in the direction parallel to the plane of the light emitting
layer 12, are formed through oxidization of the second
semiconductor layer 13 itself.
[0095] In the first embodiment, the lower portion of the oxidized
regions 13a does not reach the light emitting layer 12. Moreover,
in the case of a light emitting diode device, the oxidized region
13a is formed in a ring shape along the periphery of chips, into
which the second semiconductor layer 13 is divided. On the other
hand, in the case of a semiconductor laser device, it is formed
along opposing sides of each chip so as to obtain a cavity
structure.
[0096] A p-side electrode 14, which is a first ohmic electrode made
of a nickel (Ni)-gold (Au) laminate, is formed across the entire
surface of the second semiconductor layer 13 including the oxidized
regions 13a. Moreover, an n-side electrode 15, which is a second
ohmic electrode made of a titanium (Ti)-aluminum (Al) laminate, is
formed on one surface of the first semiconductor layer 11 that is
away from the second semiconductor layer 13.
[0097] Herein, for example, the first semiconductor layer 11 may be
an n-type cladding layer made of n-type aluminum gallium nitride
(AlGaN) with an n-type gallium nitride (GaN) layer being provided
on the side of the n-side electrode 15, and the second
semiconductor layer 13 may be a p-type cladding layer made of
p-type aluminum gallium nitride with a p-type gallium nitride layer
being provided on the side of the p-side electrode 14. Moreover,
the light emitting layer 12 may have a quantum well structure using
indium gallium nitride (InGaN) in the well layer.
[0098] Furthermore, a contact layer made of gallium nitride, for
example, may be provided on the inner side of each of the n-side
electrode 15 and the p-side electrode 14.
[0099] Note that the oxidized regions 13a may alternatively be
provided in the first semiconductor layer 11 instead of in the
second semiconductor layer 13.
[0100] Moreover, the upper surface of the oxidized regions 13a and
that of the second semiconductor layer 13 do not have to be flush
with each other.
[0101] Moreover, the conductivity type of the first semiconductor
layer 11 and that of the second semiconductor layer 13 may be
exchanged.
[0102] As described above, the semiconductor device of the first
embodiment does not have a single-crystal substrate for growing the
first semiconductor layer 11, the light emitting layer 12 and the
second semiconductor layer 13, whereby the p-side electrode 14 and
the n-side electrode 15 are provided so as to oppose each other via
the light emitting layer 12 therebetween. Thus, it is possible to
significantly reduce the series resistance value between the p-side
electrode 14 and the n-side electrode 15. In addition, the oxidized
regions 13a, which are spaced apart from each other in the
direction parallel to the plane of the light emitting layer 12,
form a current constriction section without being dry-etched.
Therefore, side portions of the light emitting layer 12 are not
subject to an etching damage, whereby it is possible to
significantly reduce the leakage current in the light emitting
layer 12 during the operation of the device. As a result, it is
possible to reliably reduce the operating current of a light
emitting diode device, or the threshold current value of a
semiconductor laser device.
[0103] Moreover, as described above, the device does not have a
substrate made of sapphire, which is normally used, whereby the
semiconductor layers 11 and 13 including the light emitting layer
12 can be cleaved in the orientation that is inherent to a gallium
nitride semiconductor without being bound by the orientation of
sapphire. As a result, in the case of a semiconductor laser device,
a cavity having a desirable cleaved surface can be obtained,
whereby improvements in the operating characteristics of the device
can be achieved, such as a reduction in the threshold current
value.
First Manufacturing Method of First Embodiment
[0104] A method for manufacturing a semiconductor device having
such a structure will be described with reference to the
drawings.
[0105] FIG. 2A to FIG. 2E are cross-sectional views sequentially
illustrating steps in a first method for manufacturing a
semiconductor device according to the first embodiment of the
present invention.
[0106] First, as illustrated in FIG. 2A, the first semiconductor
layer 11, which is an n-type cladding layer made of n-type aluminum
gallium nitride, the light emitting layer 12 containing indium
gallium nitride, and the second semiconductor layer 13, which is a
p-type cladding layer made of p-type aluminum gallium nitride, are
grown in this order on a substrate 20 made of sapphire
(single-crystal Al.sub.2O.sub.3) by a metal organic chemical vapor
deposition (MOCVD) method, for example. Herein, a portion of the
first semiconductor layer 11 in the vicinity of the interface with
the substrate 20 may be made of gallium nitride so that the portion
serves as a contact layer for the n-side electrode. Similarly, a
portion of the second semiconductor layer 13 in the vicinity of the
upper surface thereof may be made of gallium nitride so that the
portion serves as a contact layer for the p-side electrode.
[0107] Moreover, for example, trimethylgallium (TMGa),
trimethylaluminum (TMAl) and trimethylindium (TMIn) are used as a
group III source, and ammonia (NH.sub.3) is used as a nitrogen
source. Moreover, the n-type dopant may be a monosilane (SiH.sub.4)
gas, for example, and the p-type dopant may be biscyclopentadienyl
magnesium (Cp.sub.2Mg), for example.
[0108] Next, as illustrated in FIG. 2B, a mask-forming film made of
silicon (Si) obtained through decomposition of monosilane
(SiH.sub.4) is deposited on the second semiconductor layer 13 by a
chemical vapor deposition (CVD) method, for example, and an
oxidization mask film 31 is formed from the deposited mask-forming
film by a photolithography method and a dry etching method. In the
case of a light emitting diode device, the oxidization mask film 31
is arranged in the central portion so that a peripheral portion of
the device (chip), i.e., the second semiconductor layer 13, is
exposed. Moreover, in the case of a semiconductor laser device, it
is arranged in a stripe pattern along the current constriction
section of the second semiconductor layer 13.
[0109] Next, as illustrated in FIG. 2C, the second semiconductor
layer 13 with the oxidization mask film 31 formed thereon is
subjected to a heat treatment at a temperature of 900.degree. C.
for about 4 hours, for example, in an oxidizing atmosphere
containing an oxygen (O.sub.2) gas, for example. Herein, the
oxidizing atmosphere may be water vapor (H.sub.2O). Thus, the
oxidized regions 13a, which are spaced apart from each other in the
direction parallel to the plane of the light emitting layer 12, are
formed in the second semiconductor layer 13. Thus, by using an
oxygen gas or water vapor as the oxidizing atmosphere, it is
possible to form the oxidized regions 13a within a short period of
time and with a good reproducibility.
[0110] Next, as illustrated in FIG. 2D, the oxidization mask film
31 is removed by hydrofluoric-nitric acid, for example, and then
the p-side electrode 14 made of a nickel-gold laminate is formed
across the entire surface of the second semiconductor layer 13
including the oxidized regions 13a by using an electron beam
deposition method, for example. Then, one surface of the substrate
20 that is away from the first semiconductor layer 11 is irradiated
with krypton fluoride (KrF) pulsed excimer laser light having a
wavelength of 248 nm so as to scan the entire surface of the
substrate 20. Thus, the radiated excimer laser light is not
absorbed by the substrate 20 but is absorbed by the first
semiconductor layer 11, whereby the first semiconductor layer 11 is
heated. This heat thermally decomposes gallium nitride, whereby the
substrate 20 and the first semiconductor layer 11 are separated
from each other. Herein, the peak power density and the pulse width
of the excimer laser light are set so that gallium nitride bound to
the substrate 20 is decomposed. Thus, by oscillating excimer laser
light in a pulsed manner, the output power of the laser light can
be increased significantly, whereby the substrate 20 can easily be
separated from the first semiconductor layer 11. In addition, since
the excimer laser light is radiated so as to scan the surface of
the substrate 20, the substrate 20 can reliably be separated even
if the substrate 20 has a relatively large area, irrespective of
the beam diameter of the light source.
[0111] Moreover, the substrate 20 may be irradiated with excimer
laser light while heating the substrate 20 to a temperature of
about 500.degree. C. so as to relieve the stress that occurs during
the cooling process after the crystal growth due to the difference
between the coefficient of thermal expansion of a nitride
semiconductor and that of sapphire.
[0112] Moreover, the irradiation light may alternatively be the
tertiary harmonic wave of YAG (Yttrium Aluminum Garnet) laser
having a wavelength of 355 nm, or the emission line of a mercury
(Hg) lamp having a wavelength of 365 nm, instead of KrF excimer
laser light.
[0113] For example, when the emission line of a mercury lamp is
used, although the optical output power is less than that of a
laser system, the spot size can be made larger, whereby the
substrate 20 can be separated within a shorter period of time.
[0114] Furthermore, the substrate 20 may be separated from the
first semiconductor layer 11 by methods other than irradiation with
light, including removal of the substrate 20 by a polishing
method.
[0115] Herein, when the light irradiation method is used as a
method for separating the substrate 20, the separation can be done
with a reduced damage to the first semiconductor layer 11, and the
separation can be done easily even if the substrate 20 is warped.
On the other hand, when a polishing method is used, the
manufacturing cost can be reduced because the need for a light
source such as a laser system is eliminated.
[0116] Next, as illustrated in FIG. 2E, the n-side electrode 15
made of a titanium-aluminum laminate is formed on one surface of
the first semiconductor layer 11 that is away from the light
emitting layer 12 by an electron beam deposition method, for
example.
Second Manufacturing Method of First Embodiment
[0117] A second manufacturing method of the first embodiment of the
present invention will now be described with reference to the
drawings.
[0118] FIG. 3A to FIG. 3E are cross-sectional views sequentially
illustrating steps in the second method for manufacturing a
semiconductor device according to the first embodiment of the
present invention. While the deposition process of the first
manufacturing method starts from the first semiconductor layer 11,
the deposition process of the second manufacturing method proceeds
in the reverse order, starting from the second semiconductor layer
13. In FIG. 3A to FIG. 3E, those components that are already shown
in FIG. 2A to FIG. 2E are denoted by the same reference
numerals.
[0119] First, as illustrated in FIG. 3A, a lower second
semiconductor layer 13A made of p-type aluminum gallium nitride is
grown on the substrate 20 by an MOCVD method. Then, the oxidization
mask film 31 made of silicon is selectively formed on the lower
second semiconductor layer 13A in a manner similar to that of the
first manufacturing method.
[0120] Next, as illustrated in FIG. 3B, the lower second
semiconductor layer 13A with the oxidization mask film 31 formed
thereon is subjected to a heat treatment at a temperature of
900.degree. C. for about 4 hours, for example, in an oxidizing
atmosphere containing an oxygen gas or water vapor. Thus, the
oxidized regions 13a, which are spaced apart from each other in the
direction parallel to the substrate surface, are formed in the
lower second semiconductor layer 13A.
[0121] Next, as illustrated in FIG. 3C, the oxidization mask film
31 is removed by hydrofluoric-nitric acid, for example, and then
the upper second semiconductor layer 13B made of p-type aluminum
gallium nitride, the light emitting layer 12 and the first
semiconductor layer 11 made of n-type aluminum gallium nitride are
grown in this order on the lower second semiconductor layer 13A
again by an MOCVD method. Herein, the lower second semiconductor
layer 13A and the upper second semiconductor layer 13B are
collectively referred to as the second semiconductor layer 13.
Moreover, the composition of a portion of the lower second
semiconductor layer 13A in the vicinity of the substrate 20 may be
gallium nitride, and the composition of a portion of the first
semiconductor layer 11 in the vicinity of the upper surface thereof
may be gallium nitride.
[0122] Next, as illustrated in FIG. 3D, the n-side electrode 15
made of a titanium-aluminum laminate is formed through a vapor
deposition process on the first semiconductor layer 11. Then, one
surface of the substrate 20 that is away from the lower second
semiconductor layer 13A is irradiated with KrF excimer laser light
so as to scan the entire surface of the substrate 20, thereby
separating the substrate 20 from the second semiconductor layer 13.
Herein, it is preferred that the laser light oscillates in a pulsed
manner, and it is preferred that the substrate 20 is heated to a
temperature of about 500.degree. C. while being irradiated with the
laser light. Moreover, the separation/removal of the substrate 20
may be done by using the emission line of a mercury lamp or by a
polishing method.
[0123] Next, as illustrated in FIG. 3E, the p-side electrode 14
made of a nickel-gold laminate is formed on one surface of the
second semiconductor layer 13 that is away from the light emitting
layer 12.
[0124] Note that while an MOCVD method is used as the crystal
growth method for the semiconductor layers 11 and 13 including the
light emitting layer 12 in the first manufacturing method and the
second manufacturing method, a molecular beam epitaxy (MBE) method
may alternatively be used at least for the growth of the light
emitting layer 12.
[0125] Furthermore, a portion of the first semiconductor layer 11
and the second semiconductor layer 13 may be deposited by a hydride
vapor phase epitaxy (HVPE) method.
[0126] An HVPE method has a growth rate of 100 .mu.m/h or more,
which is considerably higher than those of an MOCVD method and an
MBE method, it is possible to easily increase the thickness of the
first and second semiconductor layers 11 and 13. Moreover, by
increasing the thickness of the semiconductor layers 11 and 13, the
handling of the substrate 20 in the form of a wafer after the
deposition process is made easier. In addition, improvements in the
crystallinity can also be expected from the high-speed growth
process. Therefore, a growth layer grown by an HVPE method and
having a thickness of 10 .mu.m or more, for example, may be
included in at least one of the first semiconductor layer 11 and
the second semiconductor layer 13.
[0127] Therefore, in a case where the light emitting layer 12
includes a quantum well structure, if the light emitting layer 12
is deposited by an MOCVD method or an MBE method, with which a
multi-layer structure made of films that are as thin as a few atoms
can be controlled easily and reproducibly, improvements in the
operating characteristics of a semiconductor laser device can be
achieved, such as a reduction in the threshold current value.
Moreover, when the semiconductor layers 11 and 13 are deposited by
an HVPE method having a high growth rate, it is easy to increase
the thickness thereof. Therefore, the device structure including a
quantum well structure can be formed efficiently, whereby it is
possible to obtain a semiconductor device having desirable
operating characteristics at a low cost.
[0128] Moreover, the material of the oxidization mask film 31 for
selectively forming the oxidized regions 13a is not limited to
silicon, but may alternatively be any other material that is less
likely to be oxidized as compared with a gallium nitride
semiconductor, e.g., silicon nitride (Si.sub.3N.sub.4).
First Variation of First Embodiment
[0129] A first variation of the first embodiment of the present
invention will now be described with reference to the drawings.
[0130] FIG. 4A to FIG. 4C are cross-sectional views sequentially
illustrating steps in a method for manufacturing a semiconductor
device according to the first variation of the first embodiment of
the present invention.
[0131] First, as illustrated in FIG. 4A, the second semiconductor
layer 13, the oxidized regions 13a, the light emitting layer 12 and
the first semiconductor layer 11 are formed on the substrate 20
made of sapphire, and then a support substrate 40 made of n-type
silicon (Si) oriented along the (100) plane is bonded to the upper
surface of the first semiconductor layer 11 by a known bonding
method. In this process, if the support substrate 40 is bonded so
that the cleaved surface of the support substrate 40 and that of
the first semiconductor layer 11 are parallel to each other, it is
possible to easily and reliably cleave the semiconductor layers 11
and 13 including the support substrate 40.
[0132] Next, as illustrated in FIG. 4B, one surface of the
substrate 20 that is away from the lower second semiconductor layer
13A is irradiated with pulsed KrF excimer laser light so as to scan
the entire surface of the substrate 20, thereby separating the
substrate 20 from the second semiconductor layer 13. Herein, the
separation/removal of the substrate 20 may be done by using the
emission line of a mercury lamp or by a polishing method.
[0133] Next, as illustrated in FIG. 4C, an n-side electrode 16 made
of an alloy of gold (Au) and antimony (Sb) (an Au--Sb alloy) is
formed on the upper surface of the first semiconductor layer 11.
Then, the p-side electrode 14 made of a nickel-gold laminate is
formed on one surface of the second semiconductor layer 13 that is
away from the light emitting layer 12.
[0134] Note that if the support substrate 40 made of a material
having a better heat radiating property than that of the substrate
20, e.g., copper (Cu), is bonded, the heat radiating property of
the semiconductor device is further improved.
[0135] Note that the material of the support substrate 40 is not
limited to silicon, but may alternatively be gallium arsenide
(GaAs), gallium phosphide (GaP) or indium phosphide (InP). Thus,
where the semiconductor device is a semiconductor laser device, for
example, it is possible to reduce the threshold current value and
to increase the operating lifetime of the device.
[0136] Moreover, the conductivity type of the first semiconductor
layer 11 and that of the second semiconductor layer 13 may be
switched around.
Second Variation of First Embodiment
[0137] A second variation of the first embodiment of the present
invention will now be described with reference to the drawings.
[0138] FIG. 5 is a cross-sectional view illustrating a
semiconductor device according to the second variation of the first
embodiment of the present invention. In FIG. 5, those components
that are already shown in FIG. 1 are denoted by the same reference
numerals, and will not be further described below.
[0139] As illustrated in FIG. 5, oxidized regions 13b of the
semiconductor device of the second variation are formed so as to
include the light emitting layer 12 and an upper portion of the
n-type first semiconductor layer 11. Thus, the externally injected
current can be constricted more reliably, thereby further reducing
the leakage current in the light emitting layer 12.
[0140] With the first manufacturing method, the oxidized regions
13b can be formed by growing the structure up to the second
semiconductor layer 13, and then oxidizing the structure until the
oxidized regions 13b reach the upper portion of the first
semiconductor layer 11. Moreover, with the second manufacturing
method, the oxidized regions 13b can be formed by growing the
p-type second semiconductor layer 13, the light emitting layer 12
and a (lower) portion the n-type first semiconductor layer 11, and
then selectively oxidizing these growth layers. Then, the rest of
the first semiconductor layer 11 can be re-grown.
[0141] Note that the conductivity type of the first semiconductor
layer 11 and that of the second semiconductor layer 13 may be
switched around.
[0142] Moreover, in the first embodiment and the variation thereof,
a single-crystal substrate of magnesium oxide (MgO) or lithium
gallium aluminum oxide (LiGa.sub.xAl.sub.1-xO.sub.2 (where
0.ltoreq.x.ltoreq.1)) may be used for the substrate 20, instead of
sapphire. Since a single-crystal substrate of these materials has a
lattice constant close to that of a group III-V nitride
semiconductor, a nitride semiconductor crystal grows desirably on
such a substrate, whereby it is possible to realize a
high-performance light emitting device, i.e., a light emitting
diode device or a semiconductor laser device, capable of emitting
visible light such as blue light or blue-violet light.
[0143] Also in the second variation, the upper surface of the
oxidized regions 13a and that of the second semiconductor layer 13
do not have to be flush with each other.
Second Embodiment
[0144] The second embodiment of the present invention will now be
described with reference to the drawings.
[0145] FIG. 6 is a cross-sectional view illustrating, as a
semiconductor device according to the second embodiment of the
present invention, a semiconductor light emitting device that can
be applied to a light emitting diode device or a semiconductor
laser device. In FIG. 6, those components that are already shown in
FIG. 1 are denoted by the same reference numerals, and will not be
further described below.
[0146] In the semiconductor device of the second embodiment, a
substrate 21 made of p-type silicon carbide (SIC) oriented along
the (0001) plane, for example, is provided on one surface of the
p-type second semiconductor layer 13 that is away from the light
emitting layer 12.
[0147] Moreover, a p-side electrode 17 as the first ohmic electrode
made of an alloy of aluminum (Al) and silicon (Si), e.g., an Al-Si
alloy (Al: 89%), is formed on one surface of the substrate 21 that
is away from the second semiconductor layer 13.
[0148] Thus, according to the second embodiment, the substrate 21,
which is electrically conductive, is provided on the second
semiconductor layer 13, whereby the p-side electrode 17 and the
n-side electrode 15 can be formed so as to oppose each other via
the light emitting layer 12 therebetween. Thus, it is possible to
significantly reduce the series resistance value between the p-side
electrode 17 and the n-side electrode 15. In addition, the oxidized
regions 13a, which are spaced apart from each other in the
direction parallel to the plane of the light emitting layer 12,
form a current constriction section without being dry-etched.
Therefore, side portions of the light emitting layer 12 are not
subject to an etching damage, whereby it is possible to
significantly reduce the leakage current in the light emitting
layer 12 during the operation of the device. As a result, it is
possible to reduce the operating current of a light emitting diode
device or the threshold current value of a semiconductor laser
device.
[0149] Furthermore, since silicon carbide, which has a better heat
radiating property than that of sapphire is used for the substrate
21, it is possible to further increase the operating lifetime of
the semiconductor device.
[0150] Note that the upper surface of the oxidized regions 13a and
that of the second semiconductor layer 13 do not have to be flush
with each other.
[0151] Moreover, the conductivity type of the first semiconductor
layer 11 and that of the second semiconductor layer 13 may be
switched around.
[0152] Moreover, the extent of the oxidized regions 13a is not
limited to within the second semiconductor layer 13, but the
oxidized regions 13a may alternatively be formed so as to reach the
light emitting layer 12 or the first semiconductor layer 11.
[0153] Moreover, the material of the substrate 21 may alternatively
be silicon (Si), gallium arsenide (GaAs), gallium phosphide (GaP),
indium phosphide (InP), zinc oxide (ZnO) or a metal such as copper
(Cu), instead of silicon carbide. Since zinc oxide, for example,
has a lattice constant close to that of a group III-V nitride
semiconductor, and any of silicon, gallium arsenide, gallium
phosphide and indium phosphide has a desirable crystallinity, a
nitride semiconductor crystal grows desirably on such a substrate,
whereby it is possible to realize a high-performance light emitting
device, i.e., a light emitting diode device or a semiconductor
laser device, capable of emitting visible light such as blue light
or blue-violet light.
[0154] Moreover, when using a metal, a desirable heat radiating
property is obtained. Therefore, in the case of a semiconductor
laser device, for example, the semiconductor laser device can
operate under high temperatures, and the operating lifetime of the
semiconductor laser device can be increased.
[0155] A method for manufacturing a semiconductor device having
such a structure will now be described with reference to the
drawings.
[0156] FIG. 7A to FIG. 7D are cross-sectional views sequentially
illustrating steps in a method for manufacturing a semiconductor
device according to the second embodiment of the present
invention.
[0157] Herein, a method in which the second semiconductor layer 13,
the light emitting layer 12 and the first semiconductor layer 11
are deposited in this order on the substrate 21, as in the second
manufacturing method of the first embodiment, will be
described.
[0158] First, as illustrated in FIG. 7A, the lower second
semiconductor layer 13A made of p-type aluminum gallium nitride is
grown on the substrate 21 made of p-type silicon carbide by an
MOCVD method. Then, the oxidization mask film 31 made of silicon is
selectively formed on the lower second semiconductor layer 13A, as
in the first embodiment.
[0159] Next, as illustrated in FIG. 7B, the lower second
semiconductor layer 13A with the oxidization mask film 31 formed
thereon is subjected to a heat treatment at a temperature of
900.degree. C. for about 4 hours, for example, in an oxidizing
atmosphere containing an oxygen gas or water vapor. Thus, the
oxidized regions 13a, which are spaced apart from each other in the
direction parallel to the substrate surface, are formed in the
lower second semiconductor layer 13A.
[0160] Next, as illustrated in FIG. 7C, the oxidization mask film
31 is removed by hydrofluoric-nitric acid, for example, and then
the upper second semiconductor layer 13B made of p-type aluminum
gallium nitride, the light emitting layer 12 and the first
semiconductor layer 11 made of n-type aluminum gallium nitride are
grown in this order on the lower second semiconductor layer 13A
again by an MOCVD method. Again, the lower second semiconductor
layer 13A and the upper second semiconductor layer 13B are
collectively referred to as the second semiconductor layer 13.
Moreover, the composition of a portion of the lower second
semiconductor layer 13A in the vicinity of the substrate 21 may be
gallium nitride, and the composition of a portion of the first
semiconductor layer 11 in the vicinity of the upper surface thereof
may be gallium nitride.
[0161] Next, as illustrated in FIG. 7D, the n-side electrode 15
made of a titanium-aluminum laminate is formed across the entire
surface of the first semiconductor layer 11 by an electron beam
deposition method, for example. Then, the p-side electrode 17 made
of an Al-Si alloy (Al: 89%) is formed on one surface of the
substrate 21 that is away from the lower second semiconductor layer
13A by an electron beam deposition method, for example.
[0162] Note that while an MOCVD method is used as the crystal
growth method for the semiconductor layers 11 and 13 including the
light emitting layer 12, an MBE method may alternatively be used at
least for the deposition of the light emitting layer 12.
[0163] Furthermore, a growth layer grown by an HVPE method and
having a thickness of 10 .mu.m or more, for example, may be
included in at least one of the first semiconductor layer 11 and
the second semiconductor layer 13.
[0164] Thus, in the manufacturing method of the second embodiment,
the substrate 21 for growing semiconductor layers thereon is
electrically conductive, whereby the n-side electrode 15 and the
p-side electrode 17 can be provided so as to oppose each other
without removing the substrate 21, thus simplifying the
process.
Third Embodiment
[0165] The third embodiment of the present invention will now be
described with reference to the drawings.
[0166] FIG. 8 is a cross-sectional view illustrating, as a
semiconductor device according to the third embodiment of the
present invention, a semiconductor light emitting device that can
be applied to a light emitting diode device or a semiconductor
laser device. In FIG. 8, those components that are already shown in
FIG. 1 are denoted by the same reference numerals, and will not be
further described below.
[0167] The semiconductor device of the third embodiment is
characterized in that the exposed surfaces of the oxidized regions
13a, which form the current constriction section, are covered by an
insulating film 18 made of silicon oxide (SiO.sub.2). Moreover, the
p-side electrode 14 is selectively formed on a region of the second
semiconductor layer 13 between the oxidized regions 13a.
[0168] Thus, as in the first embodiment, the semiconductor device
of the third embodiment does not have a substrate for crystal
growth, whereby the p-side electrode 14 and the n-side electrode 15
are provided so as to oppose each other via the light emitting
layer 12 therebetween. Thus, it is possible to significantly reduce
the series resistance value between the p-side electrode 14 and the
n-side electrode 15. In addition, the oxidized regions 13a, which
are spaced apart from each other in the direction parallel to the
plane of the light emitting layer 12, form a current constriction
section without being dry-etched. Therefore, side portions of the
light emitting layer 12 are not subject to an etching damage.
[0169] In addition, the position of the p-side electrode 14 is
restricted by the insulating film 18, and the p-side electrode 14
is formed only on the exposed surface of the second semiconductor
layer 13. Therefore, a leakage current via the oxidized regions 13a
can be prevented, whereby it is possible to further suppress the
leakage current in the light emitting layer 12 during the operation
of the device. As a result, it is possible to reduce the operating
current of the semiconductor device.
[0170] Moreover, the device does not have a substrate for crystal
growth, whereby the semiconductor layers 11 and 13 including the
light emitting layer 12 can be cleaved in the orientation that is
inherent to a gallium nitride semiconductor without being bound by
the orientation of the material of the substrate. Therefore, in the
case of a semiconductor laser device, a cavity having a desirable
cleaved surface can be realized, whereby improvements in the
operating characteristics of the device can be achieved, such as a
reduction in the threshold current value.
[0171] Note that the oxidized regions 13a may alternatively be
provided in the first semiconductor layer 11 instead of in the
second semiconductor layer 13.
[0172] Moreover, the upper surface of the oxidized regions 13a and
that of the second semiconductor layer 13 do not have to be flush
with each other.
[0173] Moreover, the conductivity type of the first semiconductor
layer 11 and that of the second semiconductor layer 13 may be
switched around.
[0174] Moreover, the extent of the oxidized regions 13a is not
limited to within the second semiconductor layer 13, but the
oxidized regions 13a may alternatively be formed so as to reach the
light emitting layer 12 or the first semiconductor layer 11.
[0175] A method for manufacturing a semiconductor device having
such a structure will now be described with reference to the
drawings.
[0176] FIG. 9A to FIG. 9D and FIG. 10A to FIG. 10D are
cross-sectional views sequentially illustrating steps in a method
for manufacturing a semiconductor device according to the third
embodiment of the present invention.
[0177] Herein, a method in which layers are sequentially deposited
on the substrate 20 starting from the first semiconductor layer 11,
as in the first manufacturing method of the first embodiment, will
be described.
[0178] First, as illustrated in FIG. 9A, the first semiconductor
layer 11 made of n-type aluminum gallium nitride, the light
emitting layer 12 including indium gallium nitride in the well
layer, and the second semiconductor layer 13 made of p-type
aluminum gallium nitride are grown in this order on the substrate
20 made of sapphire by an MOCVD method, for example. Herein, a
portion of the first semiconductor layer 11 in the vicinity of the
interface with the substrate 20 may be made of gallium nitride so
that the portion serves as a contact layer for the n-side
electrode. Similarly, a portion of the second semiconductor layer
13 in the vicinity of the upper surface thereof may be made of
gallium nitride so that the portion serves as a contact layer for
the p-side electrode.
[0179] Next, as illustrated in FIG. 9B, the oxidization mask film
31 made of silicon is selectively formed on the second
semiconductor layer 13 as in the first embodiment.
[0180] Next, as illustrated in FIG. 9C, the second semiconductor
layer 13 with the oxidization mask film 31 formed thereon is
subjected to a heat treatment at a temperature of 900.degree. C.
for about 4 hours, for example, in an oxidizing atmosphere
containing an oxygen gas or water vapor. Thus, the oxidized regions
13a, which are spaced apart from each other in the direction
parallel to the plane of the light emitting layer 12, are formed in
the second semiconductor layer 13.
[0181] Next, as illustrated in FIG. 9D, the insulating film 18 made
of silicon oxide and having a thickness of about 300 nm is
deposited across the entire upper surface of the second
semiconductor layer 13 including the oxidized regions 13a by a CVD
method.
[0182] Next, as illustrated in FIG. 10A, a resist pattern 32 having
an opening pattern 32a in the electrode forming region above a
portion of the second semiconductor layer 13 that is interposed
between the oxidized regions 13a is formed on the insulating film
18 by a photolithography method.
[0183] Next, as illustrated in FIG. 10B, the insulating film 18 is
wet-etched with, for example, an aqueous solution including
hydrofluoric acid (HF) (hereinafter referred to as "hydrofluoric
acid") while using the resist pattern 32 as a mask. Thus, the
opening pattern 32a is transferred onto the insulating film 18 so
as to expose a portion of the second semiconductor layer 13 that is
interposed between the oxidized regions 13a. Then, a p-side
electrode forming film 14A made of a nickel-gold laminate is
deposited through a vapor deposition process on the resist pattern
32 including the second semiconductor layer 13.
[0184] Next, as illustrated in FIG. 10C, the p-side electrode 14
made of the p-side electrode forming film 14A is formed on a
portion of the second semiconductor layer 13 that is interposed
between the oxidized regions 13a by a so-called "lift-off" method
for removing the resist pattern 32. Then, one surface of the
substrate 20 that is away from the first semiconductor layer 11 is
irradiated with pulsed KrF excimer laser light so as to scan the
entire surface of the substrate 20. The irradiation with laser
light thermally decomposes a portion of the first semiconductor
layer 11 that is along the interface with the substrate 20, thereby
separating the substrate 20 and the first semiconductor layer 11
from each other. Herein, the substrate 20 may be heated to a
temperature of about 500.degree. C. while being irradiated with the
laser light. Moreover, the means for separating or removing the
substrate 20 may alternatively be the tertiary harmonic wave of YAG
laser having a wavelength of 355 nm, the emission line of a mercury
lamp having a wavelength of 365 nm, or a polishing method, instead
of KrF excimer laser light.
[0185] Next, as illustrated in FIG. 10D, the n-side electrode 15
made of a titanium-aluminum laminate is formed through a vapor
deposition process on one surface of the first semiconductor layer
11 that is away from the light emitting layer 12.
[0186] Thus, according to the manufacturing method of the third
embodiment, the insulating film 18 not only functions as a surface
protection film for the oxidized regions 13a, but also functions as
a spacer layer, in the step of depositing the p-side electrode
forming film 14A illustrated in FIG. 10B, for separating a portion
of the p-side electrode forming film 14A that is located on the
resist pattern 32 and another portion thereof that is located on
the second semiconductor layer 13 from each other.
[0187] Thus, the insulating film 18 is provided on the oxidized
regions 13a, and the p-side electrode 14 is formed so that the
position thereof is restricted by the insulating film 18, whereby
the production yield of the p-side electrode 14 is improved, thus
reducing the cost, in addition to the reduction in the leakage
current as described above.
[0188] Note that while silicon oxide is used for the insulating
film 18, silicon nitride (Si.sub.3N.sub.4) may alternatively be
used instead of silicon oxide. Silicon oxide and silicon nitride
can easily be removed by wet etching, and can be formed at a
relatively low temperature. Therefore, thermal damage to the light
emitting layer 12 can be suppressed, whereby the operating
characteristics of the semiconductor device will not be
deteriorated. In addition, the p-side electrode forming film 14A
can be lifted off easily and reproducibly.
[0189] Moreover, the second manufacturing method may also be
employed, in which layers are grown on the substrate 20 starting
from the second semiconductor layer 13.
[0190] Moreover, a support substrate made of silicon, or the like,
may be bonded to one surface of the second semiconductor layer 13
that is away from the light emitting layer 12 before the substrate
20 is separated from the first semiconductor layer 11, e.g.,
before: the insulating film 18 is deposited. Alternatively, a
support substrate made of silicon, or the like, may be bonded to
one surface of the first semiconductor layer 11 that is away from
the light emitting layer 12 after the separation of the substrate
20 and before the formation of the n-side electrode 15.
Fourth Embodiment
[0191] The fourth embodiment of the present invention will now be
described with reference to the drawings.
[0192] FIG. 11 is a cross-sectional view illustrating, as a
semiconductor device according to the fourth embodiment of the
present invention, a semiconductor light emitting device that can
be applied to a light emitting diode device. In FIG. 11, those
components that are already shown in FIG. 1 are denoted by the same
reference numerals, and will not be further described below.
[0193] In the semiconductor device of the fourth embodiment,
sapphire, which is insulative, is used for the substrate 20 on
which the n-type first semiconductor layer 11, the light emitting
layer 12 and the p-type second semiconductor layer 13 are to be
grown, and the substrate 20 is not separated from the first
semiconductor layer 11.
[0194] Therefore, a current constriction section 200, which is
etched so that it has a convex cross section, is formed in the
first semiconductor layer 11 and the second semiconductor layer 13
including the light emitting layer 12. The p-side electrode 14,
which is the first ohmic electrode, is formed on the second
semiconductor layer 13 in the current constriction section 200, and
the n-side electrode 15, which is the second ohmic electrode, is
formed on the exposed region of the first semiconductor layer 11
beside the current constriction section 200.
[0195] Furthermore, the fourth embodiment is characterized in that
the oxidized regions 13b are formed on the exposed surface of the
current constriction section 200, which has been exposed by dry
etching, or the like. The oxidized regions 13b are formed through
oxidization of the semiconductor layers 11 and 13, themselves,
including the light emitting layer 12 so as to interpose the light
emitting layer 12 therebetween.
[0196] Thus, according to the fourth embodiment, even with a
structure where the current constriction section 200 is provided by
dry etching, or the like, as in the prior art, the exposed surface
of the current constriction section 200 including the side portions
of the light emitting layer 12 is oxidized to form the oxidized
regions 13b. Thus, even if the exposed surface of the current
constriction section 200 is damaged by etching, the damaged portion
is oxidized and taken into the oxidized regions 13b. As a result,
the leakage current in the light emitting layer 12 is significantly
reduced, whereby the operating current of the semiconductor device
can be reduced.
[0197] Note that the conductivity type of the first semiconductor
layer 11 and that of the second semiconductor layer 13 may be
switched around.
[0198] Moreover, the first semiconductor layer 11, the light
emitting layer 12 and the second semiconductor layer 13 may be
formed by an MOCVD method or an MBE method, for example, and a
portion grown by an HVPE method to a thickness of 10 .mu.m or more
can be included in at least one of the first semiconductor layer 11
and the second semiconductor layer 13.
[0199] Moreover, a single-crystal substrate made of magnesium oxide
or lithium gallium aluminum oxide (LiGa.sub.xAl.sub.1-xO.sub.2
(where 0.ltoreq.x.ltoreq.1)) may be used for the substrate 20,
instead of sapphire.
Fifth Embodiment
[0200] The fifth embodiment of the present invention will now be
described with reference to the drawings.
[0201] FIG. 12 is a cross-sectional view illustrating, as a
semiconductor device according to the fifth embodiment of the
present invention, a semiconductor light emitting device that can
be applied to a light emitting diode device. In FIG. 12, those
components that are already shown in FIG. 11 are denoted by the
same reference numerals, and will not be further described
below.
[0202] In the semiconductor device of the fifth embodiment, the
insulating film 18 made of silicon oxide as a surface protection
film is formed on the exposed surface of the oxidized regions
13b.
[0203] Moreover, the edge portions of the p-side electrode 14 and
the n-side electrode 15 are formed so as to be laid on the edge
portions of the oxidized regions 13b.
[0204] Note that the conductivity type of the first semiconductor
layer 11 and that of the second semiconductor layer 13 may be
switched around.
[0205] Moreover, a single-crystal substrate made of magnesium oxide
or lithium gallium aluminum oxide (LiGa.sub.xAl.sub.1-xO.sub.2
(where 0.ltoreq.x.ltoreq.1)) may be used for the substrate 20,
instead of sapphire.
[0206] A method for manufacturing a semiconductor device having
such a structure will now be described with reference to the
drawings.
[0207] FIG. 13A to FIG. 13D and FIG. 14A to FIG. 14D are
cross-sectional views sequentially illustrating steps in a method
for manufacturing a semiconductor device according to the fifth
embodiment of the present invention.
[0208] First, as illustrated in FIG. 13A, the first semiconductor
layer 11 made of n-type aluminum gallium nitride, the light
emitting layer 12 including indium gallium nitride in the well
layer, and the second semiconductor layer 13 made of p-type
aluminum gallium nitride are grown in this order on the substrate
20 made of sapphire by an MOCVD method, for example. Herein, a
portion of the first semiconductor layer 11 in the vicinity of the
interface with the substrate 20 may be made of gallium nitride.
Similarly, a portion of the second semiconductor layer 13 in the
vicinity of the upper surface thereof may be made of gallium
nitride.
[0209] Next, as illustrated in FIG. 13B, the second semiconductor
layer 13, the light emitting layer 12 and an upper portion of the
first semiconductor layer 11 are sequentially dry-etched, while
masking a current constriction section forming region of the second
semiconductor layer 13, by a reactive ion etching (RE) method using
a chlorine (Cl.sub.2) gas as an etching gas, for example, thereby
forming the current constriction section 200 having a convex cross
section and including the first semiconductor layer 11, the light
emitting layer 12 and the second semiconductor layer 13.
[0210] Next, as illustrated in FIG. 13C, a mask-forming film made
of silicon is deposited on the entire upper surface of the first
semiconductor layer 11 including the current constriction section
200 by, for example, a CVD method in which monosilane is
decomposed. Then, a first oxidization mask film 31A is formed, from
the mask-forming film, on a portion of the second semiconductor
layer 13 within the current constriction section 200 for masking
the portion of the second semiconductor layer 13 excluding the
peripheral portion thereof, by a photolithography method and an
etching method. At the same time, a second oxidization mask film
31B is formed, from the mask-forming film, on the exposed region of
the first semiconductor layer 11 beside the current constriction
section 200.
[0211] Herein, in the step illustrated in FIG. 13B, if the etching
process is performed by using the first oxidization mask film 31A
as a mask, instead of using a resist mask, or the like, the
photolithography step illustrated in FIG. 13B can be omitted.
[0212] Next, as illustrated in FIG. 13D, the substrate 20 with the
first oxidization mask film 31A and the second oxidization mask
film 31B formed thereon is subjected to a heat treatment at a
temperature of about 900.degree. C. for about 4 hours in an
oxidizing atmosphere containing an oxygen gas or water vapor. Thus,
the oxidized regions 13b are formed on the surface of the current
constriction section 200 and on the exposed surface of the first
semiconductor layer 11.
[0213] Next, as illustrated in FIG. 14A, the first oxidization mask
film 31A and the second oxidization mask film 31B are removed by
hydrofluoric-nitric acid, for example. Then, the insulating film 18
made of silicon oxide and having a thickness of about 300 nm is
deposited across the entire surface of the substrate 20 including
the current constriction section 200 by a CVD method.
[0214] Next, as illustrated in FIG. 14B, a first resist pattern 33
having a first opening pattern 33a in the p-side electrode forming
region above a portion of the second semiconductor layer 13 within
the current constriction section 200 is formed on the insulating
film 18 by a photolithography method. Then, the insulating film 18
is wet-etched with, for example, hydrofluoric acid while using the
first resist pattern 33 as a mask. Thus, the first opening pattern
33a is transferred onto the insulating film 18 so as to expose the
second semiconductor layer 13. Then, the p-side electrode forming
film 14A made of a nickel-gold laminate is deposited through a
vapor deposition process on the first resist pattern 33 including
the exposed portion of the second semiconductor layer 13. Then, the
p-side electrode 14 made of the p-side electrode forming film 14A
is formed on a portion of the second semiconductor layer 13 within
the current constriction section 200 by a so-called "lift-off"
method for removing the first resist pattern 33. Herein, since the
edge portions of the oxidized regions 13b are exposed through the
first opening pattern 33a, the edge portions of the formed p-side
electrode 14 are laid on the edge portions of the oxidized regions
13b.
[0215] Next, as illustrated in FIG. 14C, a second resist pattern 34
having a second opening pattern 34a in the n-side electrode forming
region above a portion of the first semiconductor layer 11 beside
the current constriction section 200 is formed on the insulating
film 18 and the p-side electrode 14 again by a photolithography
method. Then, the insulating film 18 is wet-etched with, for
example, hydrofluoric acid while using the second resist pattern 34
as a mask. Thus, the second opening pattern 34a is transferred onto
the insulating film 18 so as to expose the first semiconductor
layer 11. Then, an n-side electrode forming film 15A made of a
titanium-aluminum laminate is deposited through a vapor deposition
process on the second resist pattern 34 including the exposed
portion of the first semiconductor layer 11.
[0216] Next, as illustrated in FIG. 14D, the n-side electrode 15
made of the n-side electrode forming film 15A is formed on the
first semiconductor layer 11 by a lift-off method for removing the
second resist pattern 34. Note that either the p-side electrode 14
and the n-side electrode 15 may be formed first.
[0217] Thus, according to the manufacturing method of the fifth
embodiment, the insulating film 18 not only functions as a surface
protection film for the oxidized regions 13a, but also functions as
a spacer layer, in the step of depositing the p-side electrode
forming film 14A illustrated in FIG. 14B, for separating a portion
of the p-side electrode forming film 14A that is located on the
first resist pattern 33 and another portion thereof that is located
on the second semiconductor layer 13 from each other. This is also
true with the n-side electrode forming film 15A.
[0218] Therefore, in the fifth embodiment, as in the fourth
embodiment, even with a structure where the current constriction
section 200 is formed by dry etching, the oxidized regions 13b are
formed through oxidization of the semiconductor layer itself on the
side surfaces of the current constriction section 200, whereby the
leakage current in the light emitting layer 12 can be reduced. As a
result, it is possible to reduce the operating current of the
semiconductor device.
[0219] In addition, the insulating film 18 is provided on the
oxidized regions 13a, and the p-side electrode 14 and the n-side
electrode 15 are formed so that the positions thereof are
restricted by the insulating film 18, whereby the production yield
of the electrodes 14 and 15 is improved, thus reducing the
cost.
[0220] Note that while silicon oxide is used for the insulating
film 18, silicon nitride (Si.sub.3N.sub.4) may alternatively be
used instead of silicon oxide.
[0221] Moreover, while an MOCVD method is used as the crystal
growth method for the semiconductor layers 11 and 13 including the
light emitting layer 12, an MBE method may alternatively be used at
least for the deposition of the light emitting layer 12.
[0222] Furthermore, a growth layer grown by an HVPE method and
having a thickness of 10 .mu.m or more, for example, may be
included in at least one of the first semiconductor layer 11 and
the second semiconductor layer 13.
Sixth Embodiment
[0223] The sixth embodiment of the present invention will now be
described with reference to the drawings.
[0224] FIG. 15 is a cross-sectional view illustrating, as a
semiconductor device according to the sixth embodiment of the
present invention, a semiconductor light emitting device that can
be applied to a semiconductor laser device. In FIG. 15, those
components that are already shown in FIG. 1 are denoted by the same
reference numerals, and will not be further described below.
[0225] The semiconductor device of the sixth embodiment includes:
the substrate 20 made of sapphire; a base layer 19 made of n-type
gallium nitride or n-type aluminum gallium nitride on the principal
surface of the substrate 20; a selective growth mask layer 41 made
of silicon oxide and having a stripe pattern or a dotted
(island-like) pattern on the base layer 19; the first semiconductor
layer 11 made of n-type aluminum gallium nitride selectively grown
on the base layer 19 exposed through the openings of the selective
growth mask layer 41; the light emitting layer 12 having a quantum
well structure, using indium gallium nitride in the well layer,
grown on the first semiconductor layer 11; and the second
semiconductor layer 13 made of p-type aluminum gallium nitride
grown on the light emitting layer 12. Note that the growth method
for selectively growing a layer from openings of the selective
growth mask layer 41 is generally called an epitaxial lateral
overgrowth (ELO) method. Moreover, the base layer 19 may be
undoped.
[0226] Moreover, a contact layer made of gallium nitride, for
example, may be provided under each of the n-side electrode 15 and
the p-side electrode 14.
[0227] The current constriction section 200, which is etched so
that it has a convex cross section, is formed in the second
semiconductor layer 13, the light emitting layer 12 and the first
semiconductor layer 11. Furthermore, the ridge portion 201 whose
width is smaller than that of the current constriction section 200
is formed in an upper portion of the second semiconductor layer 13
within the current constriction section 200. The ridge portion 201
improves the current constriction function and also functions as a
waveguide. Therefore, light produced in the waveguide is confined
in the ridge portion 201, thereby allowing for laser oscillation,
because the refractive index of the oxidized regions 13a is smaller
than those of the semiconductor layers 11 and 13.
[0228] The p-side electrode 14 as the first ohmic electrode is
formed on the upper surface of the ridge portion 201, and the
n-side electrode 15 as the second ohmic electrode is formed on the
exposed surface of the first semiconductor layer 11 beside the
current constriction section 200.
[0229] Furthermore, the sixth embodiment is characterized in that
the oxidized regions 13b are formed on the exposed surfaces first
semiconductor layer 11, the light emitting layer 12 and the second
semiconductor layer 13, which have been exposed by dry etching, or
the like. The oxidized regions 13b are formed through oxidization
of the semiconductor layers 11 and 13, themselves, including the
light emitting layer 12 so as to interpose the light emitting layer
12 therebetween.
[0230] Thus, according to the sixth embodiment, even with a
structure where the current constriction section 200 is provided by
dry etching, or the like, as in the prior art, the exposed surface
of the current constriction section 200 including the side portions
of the light emitting layer 12 is oxidized to form the oxidized
regions 13b. Thus, even if the exposed surface of the current
constriction section 200 is damaged by etching, the damaged portion
is oxidized and taken into the oxidized regions 13b. As a result,
the leakage current in the light emitting layer 12 is significantly
reduced, whereby the threshold current value of the semiconductor
laser device can be reduced.
[0231] In addition, since the first semiconductor layer 11 is
formed by an ELO method, the light emitting layer 12 grown thereon
has a desirable crystallinity and a reduced crystal defect density,
whereby it is possible to increase the operating lifetime of the
semiconductor laser device and to reduce the threshold current
value thereof.
[0232] Note that the conductivity type of the first semiconductor
layer 11 and that of the second semiconductor layer 13 may be
switched around.
[0233] Moreover, a single-crystal substrate made of magnesium oxide
or lithium gallium aluminum oxide (LiGa.sub.xAl.sub.1-xO.sub.2
(where 0.ltoreq.x.ltoreq.1)) may be used for the substrate 20,
instead of sapphire.
[0234] A method for manufacturing a semiconductor device having
such a structure will now be described with reference to the
drawings.
[0235] FIG. 16A to FIG. 16D and FIG. 17A to FIG. 17C are
cross-sectional views sequentially illustrating steps in a method
for manufacturing a semiconductor device according to the sixth
embodiment of the present invention.
[0236] First, as illustrated in FIG. 16A, the base layer 19 made of
n-type aluminum gallium nitride and having a thickness of about 0.5
.mu.m is grown on the substrate 20 made of sapphire by an MOCVD
method, for example. Then, a selective growth mask forming layer
made of silicon oxide and having a thickness of about 200 nm is
deposited on the base layer 19 by a CVD method, for example, and
then the selective growth mask layer 41 having a stripe pattern is
formed from the selective growth mask forming layer by a
photolithography method and an etching method with hydrofluoric
acid.
[0237] Next, as illustrated in FIG. 16B, the first semiconductor
layer 11 made of n-type aluminum gallium nitride and having a
thickness of about 0.5 .mu.m is selectively grown (through an ELO
process) on the exposed portions of the base layer 19 that are
exposed through the selective growth mask layer 41 again by an
MOCVD method. Thus, a structure in which the selective growth mask
layer 41 is selectively embedded in n-type aluminum gallium nitride
having a thickness of about 1 .mu.m is obtained. Herein, the
selective growth mask layer 41 may be made of any material as long
as a gallium nitride semiconductor does not substantially grow
thereon. In addition to silicon oxide, a preferred insulating film
material is silicon nitride, and a preferred metal material is
tungsten.
[0238] Therefore, portions of the first semiconductor layer 11 that
are re-grown on the selective growth mask layer 41 are grown in the
direction parallel to the substrate surface (the lateral direction)
without being influenced by the crystal conditions of the base
layer 19. Thus, the crystallinity of the first semiconductor layer
11 is better than that of the base layer 19. For example, the
crystal dislocation density, among other crystal defect densities,
is on the order of 10.sup.7 cm.sup.-2 for the base layer 19 and is
on the order of 10.sup.6 cm.sup.-2 for the first semiconductor
layer 11.
[0239] Next, as illustrated in FIG. 16C, a first resist pattern 35
is formed in a ridge portion forming region on the second
semiconductor layer 13 by a photolithography method. Then, the
second semiconductor layer 13 is dry-etched by an RME method with a
chlorine gas, for example, while using the formed first resist
pattern 35 as a mask, thereby forming the ridge portion 201 in an
upper portion of the second semiconductor layer 13.
[0240] Next, as illustrated in FIG. 16D, after the first resist
pattern 35 is removed, a second resist pattern 36 is formed in a
current constriction section forming region including the ridge
portion 201 on the second semiconductor layer 13 again by a
photolithography method. Then, the second semiconductor layer 13,
the light emitting layer 12 and an upper portion of the first
semiconductor layer 11 are sequentially dry-etched, while using the
formed second resist pattern 36 as a mask, by an RIE method using a
chlorine gas, thereby forming the current constriction section 200
including the upper portion of the first semiconductor layer 11,
the light emitting layer 12 and the second semiconductor layer
13.
[0241] Next, as illustrated in FIG. 17A, a mask-forming film made
of silicon is deposited across the entire upper surface of the
first semiconductor layer 11 including the ridge portion 201 and
the current constriction section 200 by, for example, a CVD method
in which monosilane is decomposed. Then, first oxidization mask
film 31A is formed, from the mask-forming film, on a portion of the
second semiconductor layer 13 within the ridge portion 201 for
masking the portion of the second semiconductor layer 13 excluding
the peripheral portion thereof, by a photolithography method and an
etching method. At the same time, a second oxidization mask film
31B is formed, from the mask-forming film, on the exposed region of
the first semiconductor layer 11 beside the current constriction
section 200.
[0242] Next, as illustrated in FIG. 17B, the substrate 20 with the
first oxidization mask film 31A and the second oxidization mask
film 31B formed thereon is subjected to a heat treatment at a
temperature of about 900.degree. C. for about 4 hours in an
oxidizing atmosphere containing an oxygen gas or water vapor. Thus,
the oxidized regions 13b is formed on the surface of the current
constriction section 200 and the ridge portion 201 and on the
exposed surface of the first semiconductor layer 11.
[0243] Next, as illustrated in FIG. 17C, the first oxidization mask
film 31A and the second oxidization mask film 31B are removed by
hydrofluoric-nitric acid, for example Then, the p-side electrode 14
made of a nickel-gold laminate is selectively formed on a portion
of the second semiconductor layer 13 that is exposed in the ridge
portion 201 by an electron beam deposition method, or the like.
Then, the n-side electrode 15 made of a titanium-aluminum laminate
is formed on the exposed region of the first semiconductor layer
11. Again, the p-side electrode 14 and the n-side electrode 15 may
be formed in any order.
[0244] Note that the substrate 20 may be separated from the base
layer 19 by irradiating one surface of the substrate 20 that is
away from the base layer 19 with KrF excimer laser light, or the
like.
[0245] Furthermore, the base layer 19 and the selective growth mask
layer 41 may be removed by polishing.
[0246] Moreover, the separation of the substrate 20 may be done
after bonding a support substrate made of silicon oriented along
the (100) plane or copper.
[0247] Moreover, while an MOCVD method is used as the crystal
growth method for the semiconductor layers 11 and 13 including the
light emitting layer 12, an MBE method may alternatively be used at
least for the deposition of the light emitting layer 12.
[0248] Furthermore, a growth layer grown by an HVPE method and
having a thickness of 10 .mu.m or more, for example, may be
included in at least one of the first semiconductor layer 11 and
the second semiconductor layer 13.
Seventh Embodiment
[0249] The seventh embodiment of the present invention will now be
described with reference to the drawings.
[0250] FIG. 18 is a cross-sectional view illustrating, as a
semiconductor device according to the seventh embodiment of the
present invention, a semiconductor light emitting device that can
be applied to a semiconductor laser device. In FIG. 18, those
components that are already shown in FIG. 1 are denoted by the same
reference numerals, and will not be further described below.
[0251] In the semiconductor device according to the seventh
embodiment, the ridge portion 201 having a convex cross section is
selectively provided in the p-type second semiconductor layer 13.
The oxidized regions 13a are formed through oxidization of the
second semiconductor layer 13 itself on the exposed surface of the
ridge portion 201. Thus, the oxidized regions 13a are formed so as
to be spaced apart from each other in the direction parallel to the
plane of the light emitting layer 12.
[0252] As described above, the ridge portion 201 functions not only
as a current constriction section but also as a waveguide, whereby
light produced in the waveguide is confined in the ridge portion
201, thereby allowing for laser oscillation, because the refractive
index of the oxidized regions 13a is smaller than those of the
semiconductor layers 11 and 13
[0253] Moreover, the device does not have a substrate for growing
semiconductor layers thereon, whereby the p-side electrode 14 and
the n-side electrode 15 are formed so as to oppose each other via
the light emitting layer 12 having a quantum well structure
therebetween.
[0254] Therefore, in the seventh embodiment, since the p-side
electrode 14 and the n-side electrode 15 oppose each other, the
series resistance value of the p-n junction is reduced.
[0255] Moreover, even with a structure where the ridge portion 201
is provided by dry etching, or the like, as in the prior art, the
exposed surface of the second semiconductor layer 13 in the ridge
portion 201 is oxidized to form the oxidized regions 13a. Thus,
even if the exposed surface of the ridge portion 201 is damaged by
etching, the damaged portion is oxidized and taken into the
oxidized regions 13a. As a result, the leakage current in the light
emitting layer 12 is significantly reduced, whereby the threshold
current value of the semiconductor laser device can be reduced.
[0256] Moreover, it is required to perform a dry etching step for
the second semiconductor layer 13 only once, i.e., when forming the
ridge portion 201, whereby the process can be simplified.
[0257] Note that the conductivity type of the first semiconductor
layer 11 and that of the second semiconductor layer 13 may be
switched around.
[0258] A method for manufacturing a semiconductor device having
such a structure will now be described with reference to the
drawings.
[0259] FIG. 19A to FIG. 19D and FIG. 20A to FIG. 20C are
cross-sectional views sequentially illustrating steps in a method
for manufacturing a semiconductor device according to the seventh
embodiment of the present invention.
[0260] First, as illustrated in FIG. 19A, the first semiconductor
layer 11 made of n-type aluminum gallium nitride, the light
emitting layer 12 including indium gallium nitride in the well
layer, and the second semiconductor layer 13 made of p-type
aluminum gallium nitride are grown in this order on the substrate
20 made of sapphire by an MOCVD method, for example. Herein, a
portion of the first semiconductor layer 11 in the vicinity of the
interface with the substrate 20 may be made of gallium nitride.
Similarly, a portion of the second semiconductor layer 13 in the
vicinity of the upper surface thereof may be made of gallium
nitride.
[0261] Next, as illustrated in FIG. 19B, the second semiconductor
layer 13 is dry-etched, while masking a ridge portion forming
region of the second semiconductor layer 13, by an RIE method using
a chlorine gas as an etching gas, for example, thereby forming the
ridge portion 201 having a planar stripe pattern and a convex cross
section in the second semiconductor layer 13.
[0262] Next, as illustrated in FIG. 19C, a mask-forming film made
of silicon is deposited across the entire upper surface of the
second semiconductor layer 13 including the ridge portion 201 by a
CVD method, for example, and then the oxidization mask film 31 is
formed, from the mask-forming film, on a portion of the second
semiconductor layer 13 within the ridge portion 201 for masking the
portion of the second semiconductor layer 13 excluding the
peripheral portion thereof, by a photolithography method and an
etching method.
[0263] Herein, in the step illustrated in FIG. 19B, if the etching
process is performed by using the oxidization mask film 31 as a
mask, instead of using a resist mask, or the like, the
photolithography step illustrated in FIG. 19B can be omitted.
[0264] Next, as illustrated in FIG. 19D, the second semiconductor
layer 13 with the oxidization mask film 31 formed thereon is
subjected to a heat treatment at a temperature of about 900.degree.
C. for about 4 hours in an oxidizing atmosphere containing an
oxygen gas or water vapor. Thus, the oxidized regions 13a are
formed on the exposed surface of the second semiconductor layer
13.
[0265] Next, as illustrated in FIG. 20A, the oxidization mask film
31 is removed by hydrofluoric-nitric acid, for example. Then, the
p-side electrode 14 made of a nickel-gold laminate is selectively
formed on a portion of the second semiconductor layer 13 that is
exposed in the ridge portion 201 between the oxidized regions 13a
by an electron beam deposition method, or the like. Then, one
surface of the substrate 20 that is away from the first
semiconductor layer 11 is irradiated with pulsed KrF excimer laser
light so as to scan the entire surface of the substrate 20. The
irradiation with laser light thermally decomposes a portion of the
first semiconductor layer 11 that is along the interface with the
substrate 20, thereby separating the substrate 20 and the first
semiconductor layer 11 from each other, as illustrated in FIG. 20B.
Herein, the substrate 20 may be heated to a temperature of about
500.degree. C. while being irradiated with the laser light.
Moreover, the means for separating or removing the substrate 20 may
alternatively be the tertiary harmonic wave of YAG laser, the
emission line of a mercury lamp, or a polishing method.
[0266] Next, as illustrated in FIG. 20C, the n-side electrode 15
made of a titanium-aluminum laminate is formed through a vapor
deposition process on one surface of the first semiconductor layer
11 that is away from the light emitting layer 12. Then, the
semiconductor layers 11 and 13 including the light emitting layer
12, on which the electrodes 14 and 15 have been formed, are cleaved
so as to form a cavity for oscillating laser light. At this time,
since the substrate 20 has been removed, the semiconductor layers
11 and 13 including the light emitting layer 12 can be cleaved in
the orientation that is inherent to a gallium nitride semiconductor
without being bound by the orientation of sapphire. As a result, a
cavity having a desirable cleaved surface can be obtained, whereby
improvements in the operating characteristics of the device can be
achieved, such as a reduction in the threshold current value.
[0267] Note that while an MOCVD method is used as the crystal
growth method for the semiconductor layers 11 and 13 including the
light emitting layer 12, an MBE method may alternatively be used at
least for the deposition of the light emitting layer 12.
[0268] Furthermore, a growth layer grown by an HVPE method and
having a thickness of 10 .mu.m or more, for example, may be
included in at least one of the first semiconductor layer 11 and
the second semiconductor layer 13.
[0269] Moreover, a conductive material such as silicon carbide may
alternatively be used for the substrate 20, instead of using an
insulating material such as sapphire. In this way, the need for the
step of removing the substrate 20 is eliminated.
[0270] Moreover, a support substrate made of a conductive material
such as silicon may be bonded to one surface of the first
semiconductor layer 11 that is away from the light emitting layer
12 after the separation of the substrate 20 and before the
formation of the n-side electrode 15.
[0271] Moreover, the orientation of the principal surface of the
substrate 20 or 21 of any of the embodiments and the variations
thereof described above is not limited to any particular
orientation. For example, it may of course be the (0001)
orientation, which is the typical orientation with sapphire and
silicon carbide, but the principal surface may be provided with a
so-called "off-angle" by offsetting it slightly from the (0001)
plane.
[0272] Moreover, while an ELO method is used in the sixth
embodiment, it may also be used in other embodiments or variations
thereof
[0273] Moreover, while the semiconductor devices of the embodiments
described above take a so-called "pin junction structure" in which
the undoped light emitting layer 12 is provided between the n-type
first semiconductor layer 11 and the p-type second semiconductor
layer 13, the structure is not limited to a pin junction structure.
Particularly, when the present invention is applied to a light
emitting diode device, it may take a p-n junction structure made of
the first semiconductor layer 11 and the second semiconductor layer
13.
[0274] Moreover, the material of the first semiconductor layer 11,
the light emitting layer 12 and the second semiconductor layer 13
is not limited to a group III-V nitride semiconductor.
* * * * *