U.S. patent application number 15/583176 was filed with the patent office on 2017-08-17 for nitride semiconductor light emitting device.
This patent application is currently assigned to Sharp Kabushiki Kaisha. The applicant listed for this patent is Sharp Kabushiki Kaisha. Invention is credited to Takeshi KAMIKAWA, Yoshinobu KAWAGUCHI.
Application Number | 20170237230 15/583176 |
Document ID | / |
Family ID | 38478031 |
Filed Date | 2017-08-17 |
United States Patent
Application |
20170237230 |
Kind Code |
A1 |
KAWAGUCHI; Yoshinobu ; et
al. |
August 17, 2017 |
NITRIDE SEMICONDUCTOR LIGHT EMITTING DEVICE
Abstract
A nitride semiconductor light emitting device includes a first
coat film of aluminum nitride or aluminum oxynitride formed at a
light emitting portion and a second coat film of aluminum oxide
formed on the first coat film. The thickness of the second coat
film is at least 80 nm and at most 1000 nm. Here, the thickness of
the first coat film is preferably at least 6 nm and at most 200
nm.
Inventors: |
KAWAGUCHI; Yoshinobu;
(Osaka, JP) ; KAMIKAWA; Takeshi; (Osaka,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sharp Kabushiki Kaisha |
Osaka |
|
JP |
|
|
Assignee: |
Sharp Kabushiki Kaisha
Osaka
JP
|
Family ID: |
38478031 |
Appl. No.: |
15/583176 |
Filed: |
May 1, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14881523 |
Oct 13, 2015 |
9660413 |
|
|
15583176 |
|
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|
|
12805644 |
Aug 11, 2010 |
9190806 |
|
|
14881523 |
|
|
|
|
11713760 |
Mar 5, 2007 |
7792169 |
|
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12805644 |
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Current U.S.
Class: |
438/39 |
Current CPC
Class: |
B82Y 20/00 20130101;
H01S 5/34333 20130101; H01S 5/028 20130101; H01S 5/0287 20130101;
H01S 5/221 20130101; H01S 2304/00 20130101; H01S 5/0021 20130101;
H01S 5/223 20130101; H01L 33/44 20130101; H01S 5/2231 20130101;
H01S 5/0282 20130101 |
International
Class: |
H01S 5/028 20060101
H01S005/028; H01S 5/343 20060101 H01S005/343; H01S 5/223 20060101
H01S005/223 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 8, 2006 |
JP |
2006-062636 |
Jan 29, 2007 |
JP |
2007-017547 |
Claims
1-7. (canceled)
8. A method for producing a nitride semiconductor laser device
comprising: forming a nitride semiconductor layer; forming a facet
of a cavity by cleaving the nitride semiconductor layer; forming a
first coat film of aluminum nitride or aluminum oxynitride having a
thickness of at least 6 nm and at most 200 nm on the facet of the
nitride semiconductor layer by sputtering or electron beam
evaporation; and forming a second coat film on the first coat
film.
9. The method according to claim 8, wherein the second coat film
comprises a layer of oxide, oxynitride, or nitride.
10. The method according to claim 8, wherein the second coat film
is formed by sputtering or electron beam evaporation.
11. The method according to claim 8, wherein the second coat film
has a thickness of at least 130 nm and at most 1000 nm.
12. The method according to claim 8, wherein the first coat film is
crystallized.
13. The method according to claim 8, further comprising: forming a
ridge stripe portion with an insulating layer outside the ridge
stripe portion to the nitride semiconductor layer prior to the
cleaving, wherein the first coat film is also formed on the
insulating layer outside the ridge stripe portion.
Description
PRIORITY STATEMENT
[0001] This application is a continuation under 35 U.S.C. .sctn.120
of U.S. application Ser. No. 14/881,523, filed Oct. 13, 2015, which
is a continuation of U.S. application Ser. No. 12/805,644, filed
Aug. 11, 2010, which is a continuation of U.S. application Ser. No.
11/713,760, filed Mar. 5, 2007, now U.S. Pat. No. 7,792,169, which
claims priority under 35 U.S.C. .sctn.119 to Japanese Patent
Application Nos. 2006-062636 and 2007-017547 filed with the
Japanese Patent Office on Mar. 8, 2006 and Jan. 29, 2007,
respectively, the entire contents of each of which are hereby
incorporated herein by reference.
BACKGROUND
[0002] Technical Field
[0003] The present invention relates to a nitride semiconductor
light emitting device and more particularly to a nitride
semiconductor light emitting device with improved reliability at
the time of high power drive.
[0004] Description of the Related Art
[0005] Among semiconductor light emitting devices, semiconductor
laser devices are used as light sources for reading and writing of
a signal of an optical recording medium such as CD (Compact Disk),
DVD (Digital Versatile Disk) or Blue-Ray Disk. When a semiconductor
laser device is used as a light source for writing, a higher-power
semiconductor laser device is required because of increased speed
and increased capacity of multi-layering media. Therefore, nitride
semiconductor laser devices adapted to high power, for each
wavelength of infrared, red, blue or the like, have been developed
and are still now under development.
[0006] Recently, research and development has been conducted in an
attempt to use a semiconductor laser device as an excitation light
source for phosphors, other than a light source for reading and
writing of a signal of an optical recording medium, and to use a
semiconductor laser device as illumination. Even in the case where
a semiconductor laser device is used as illumination, a
higher-power semiconductor laser device is important to achieve
higher efficiency and higher power of a semiconductor laser
device.
[0007] Poor reliability resulting from degradation of a light
emitting portion on a facet at the light emitting side is known as
a big problem in achieving higher power of a semiconductor laser
device. This is commonly known as COD (Catastrophic Optical Damage)
which is a phenomenon in which the light emitting portion is
thermally melted thereby causing emission stop. The optical power
at which COD occurs is referred to as a COD level. The reason why
COD occurs is that the light emitting portion becomes an absorption
region in which laser light is absorbed. It is said that
non-radiative recombination level is attributable to the absorption
region.
[0008] In order to improve the COD level, generally, a window
structure is formed by widening a bandgap of a light emitting
portion for transmitting laser light, or a facet at the light
emitting side is coated with a dielectric film for protection (see,
for example, Japanese Patent Laying-Open Nos. 2002-237648 and
2002-335053).
SUMMARY
[0009] FIG. 13 shows the relation between aging time and driving
current when an aging test is conducted in which a conventional
nitride semiconductor laser device is CW (Continuous Wave) driven
in a temperature environment of 70.degree. C. to continuously emit
high-power laser light with an optical power of 100 mW. Here, after
the aging time of a few tens of hours passed, a driving current
value becomes 0, which indicates that laser light emission stops at
that time point.
[0010] The light emitting portion of the nitride semiconductor
laser device in which laser light emission stops is found to have a
hole which may be created as the light emitting portion is melted,
and it is understood that the degradation of the light emitting
portion causes emission stop. A coat film made of aluminum (Al)
nitride is formed at a thickness of 50 nm on the facet at the light
emitting side of the conventional nitride semiconductor laser
device.
[0011] The problem of reduced reliability due to degradation of the
light emitting portion at the time of high power drive is not
exclusive to nitride semiconductor laser devices but is common to
nitride semiconductor light emitting diode devices.
[0012] An object of the present invention is therefore to provide a
nitride semiconductor light emitting device with improved
reliability at the time of high power drive.
[0013] The present invention provides a nitride semiconductor light
emitting device including a first coat film of aluminum nitride or
aluminum oxynitride formed at a light emitting portion and a second
coat film of aluminum oxide formed on the first coat film. The
second coat film has a thickness of at least 80 nm and at most 1000
nm.
[0014] Preferably, in the nitride semiconductor light emitting
device according to the present invention, a thickness of the first
coat film is at least 6 nm and at most 200 nm.
[0015] Preferably, in the nitride semiconductor light emitting
device according to the present invention, a thickness of the first
coat film is at least 12 nm and at most 200 nm.
[0016] Preferably, in the nitride semiconductor light emitting
device according to the present invention, a thickness of the first
coat film is at least 50 nm and at most 200 nm. More preferably, in
the nitride semiconductor light emitting device according to the
present invention, a thickness of the second coat film is at least
130 nm and at most 1000 nm.
[0017] More preferably, in the nitride semiconductor light emitting
device according to the present invention, a thickness of the
second coat film is at least 150 nm and at most 1000 nm.
[0018] Most preferably, in the nitride semiconductor light emitting
device according to the present invention, a thickness of the
second coat film is at least 160 nm and at most 1000 nm.
[0019] Preferably, in the nitride semiconductor light emitting
device according to the present invention, the first coat film is
made of aluminum oxynitride, and the first coat film has an oxygen
content of at most 20 atomic %.
[0020] In accordance with the present invention, it is possible to
provide a nitride semiconductor light emitting device with improved
reliability at the time of high power drive.
[0021] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a cross section schematically showing a nitride
semiconductor laser device in accordance with a first embodiment of
the present invention.
[0023] FIG. 2 is a side view schematically showing the nitride
semiconductor laser device in the first embodiment of the present
invention shown in FIG. 1 in the cavity length direction.
[0024] FIG. 3 schematically shows a configuration of an exemplary
ECR sputtering apparatus.
[0025] FIG. 4 shows a result of an aging test in high power drive
for the nitride semiconductor laser device in the first
embodiment.
[0026] FIG. 5 shows a result of an aging test in high power drive
for a nitride semiconductor laser device fabricated for
comparison.
[0027] FIG. 6 shows a result of an aging test in low power drive
for a nitride semiconductor laser device fabricated for
comparison.
[0028] FIG. 7 shows a result of an aging test in high power drive
for a nitride semiconductor laser device fabricated for
comparison.
[0029] FIG. 8 shows a result of an aging test in high power drive
for a nitride semiconductor laser device fabricated to include an
aluminum oxynitride film on a facet at the light emitting side with
a thickness fixed at 6 nm and an aluminum oxide film formed on the
aluminum oxynitride film with varied thicknesses.
[0030] FIG. 9 shows a result of an aging test in high power drive
for a nitride semiconductor laser device fabricated to include an
aluminum oxynitride film on a facet at the light emitting side with
varied thicknesses and an aluminum oxide film formed on the
aluminum oxynitride film with a thickness fixed at 80 nm.
[0031] FIG. 10 shows a result of an aging test in high power drive
for a nitride semiconductor laser device in accordance with a
second embodiment.
[0032] FIG. 11 shows a result of an aging test in high power drive
for a nitride semiconductor laser device in accordance with a third
embodiment.
[0033] FIG. 12 shows a result of an aging test in high power drive
for a nitride semiconductor laser device in accordance with a
fourth embodiment.
[0034] FIG. 13 shows a result of an aging test in high power drive
for a conventional nitride semiconductor laser device.
[0035] FIG. 14 shows a result of an aging test in high power drive
for a nitride semiconductor laser device in accordance with a fifth
embodiment.
[0036] FIG. 15 shows a result of an aging test in high power drive
for a nitride semiconductor laser device in accordance with a sixth
embodiment.
DETAILED DESCRIPTION
[0037] In the following, embodiments of the present invention will
be described. It is noted that the same reference characters
represent the same or corresponding parts in the drawings of the
present invention.
[0038] As a result of elaborate study, the inventor has found that
reliability at the time of high power drive of a nitride
semiconductor light emitting device can be improved enough by
forming a first coat film made of aluminum nitride or aluminum
oxynitride on a light emitting portion of the nitride semiconductor
light emitting device and forming a second coat film made of
aluminum oxide on the first coat film with a thickness of 80 nm or
thicker. The present invention has thus been completed.
[0039] The inventor has also found that if the thickness of the
second coat film is 130 nm or thicker, the reliability at the time
of high power drive of the nitride semiconductor light emitting
device can be improved more.
[0040] The inventor has also found that if the thickness of the
second coat film is 150 nm or thicker, the reliability at the time
of high power drive of the nitride semiconductor light emitting
device can be improved further.
[0041] The inventor has also found that if the thickness of the
second coat film is 160 nm or thicker, the reliability at the time
of high power drive of the nitride semiconductor light emitting
device can be particularly improved. In addition, as a result of
elaborate study, the inventor has found that reliability at the
time of high power drive of the nitride semiconductor light
emitting device tends to be improved as the thickness of the first
coat film made of aluminum nitride or aluminum oxynitride is set to
6 nm or thicker, 12 nm or thicker, 50 nm or thicker. Therefore, the
thickness of the first coat film made of aluminum nitride or
aluminum oxynitride is preferably 6 nm or thicker, more preferably
12 nm or thicker, and even more preferably 50 nm or thicker.
[0042] If the first coat film is too thick, the first coat film
easily peels off. Therefore, the thickness of the first coat film
is preferably 200 nm or thinner. On the other hand, even if the
second film is thick, the second film does not easily peel off.
However, in view of productivity, the thickness of the second coat
film is set to 1000 nm or thinner.
[0043] In the case where the first coat film is made of aluminum
oxynitride, if the oxygen content of the first coat film is higher
than 20 atomic % of the total atoms that constitute the first coat
film, in effect, similarly to the case where a film made of
aluminum oxide is directly formed at the light emitting portion of
the nitride semiconductor light emitting device, the reliability at
the time of high power drive cannot be improved enough.
Accordingly, the oxygen content of the first coat film made of
aluminum oxynitride is preferably 20 atomic % or lower of the total
atoms that constitute the first coat film.
[0044] Here, the nitride semiconductor light emitting device of the
present invention includes, for example, a nitride semiconductor
laser device, a nitride semiconductor light emitting diode device,
or the like. Further, the nitride semiconductor light emitting
device of the present invention means a semiconductor light
emitting device including an active layer and a cladding layer
formed on a substrate which are formed of a material including 50
mass % or more of a compound made of a group 3 element of at least
one kind selected from the group consisting of aluminum, indium and
gallium, and nitrogen as a group 5 element.
First Embodiment
[0045] FIG. 1 is a cross section schematically showing a nitride
semiconductor laser device in the present embodiment. Here, a
nitride semiconductor laser device 10 in the present embodiment is
configured to include a buffer layer 21 having a thickness of 0.2
.mu.m made of n-type GaN, an n-type cladding layer 22 having a
thickness of 2.3 .mu.m made of n-type Al.sub.0.06Ga.sub.0.94N, an
n-type guide layer 23 having a thickness of 0.02 .mu.m made of
n-type GaN, a multiple quantum well active layer 24 made of 4
nm-thick InGaN and 8 nm-thick GaN, a protective layer 25 having a
thickness of 70 nm made of GaN, a p-type current block layer 26
having a thickness of 20 nm made of p-type Al.sub.0.3Ga.sub.0.7N, a
p-type cladding layer 27 having a thickness of 0.5 .mu.m made of
p-type Al.sub.0.05Ga.sub.0.95N, and a p-type contact layer 28
having a thickness of 0.1 .mu.m made of p-type GaN, which are
stacked on a semiconductor substrate 11 made of n-type GaN in this
order from semiconductor substrate 11. Here, the thickness and
mixed crystal ratio in each of the above-noted layers is adjusted
as appropriate and is irrelevant to the essence of the present
invention. The wavelength of laser light emitted from nitride
semiconductor laser device 10 in the present embodiment is
adjusted, for example, in the range of 370 nm-470 nm as appropriate
according to the mixed crystal ratio of multiple quantum well
active layer 24. In the present embodiment, the wavelength of
emitted laser light is adjusted to 405 nm. Multiple quantum well
active layer 24 may also include at least one kind of group 5
elements such as As or P by at least 0.01 atomic % and at most 10
atomic %.
[0046] Nitride semiconductor laser device 10 in the present
embodiment is formed in such a manner that p-type cladding layer 27
and p-type contact layer 28 are partially removed so that a
stripe-like ridge stripe portion 13 extends in the cavity length
direction. Here, the width of the stripe of ridge stripe portion 13
is, for example, about 1.2-2.4 .mu.m, typically about 1.5 .mu.m.
The present invention is also applicable to a broad area type
nitride semiconductor laser device for use in illumination with the
stripe width of a few tens of .mu.m. In addition, a p-electrode 14
made of a multilayer of a Mo layer and an Au layer is provided on a
surface of p-type contact layer 28. An insulating film 12 made of a
multilayer of an SiO.sub.2 layer and a TiO.sub.2 layer is provided
under p-electrode 14 at a part excluding the part where ridge
stripe portion 13 is formed. In addition, an n-electrode 15 made of
a multilayer of an Hf layer and an Al layer is formed on the
surface of semiconductor substrate 11 that is opposite to the side
where the above-noted nitride semiconductor layers are stacked.
[0047] FIG. 2 is a side view schematically showing the nitride
semiconductor laser device in the present embodiment shown in FIG.
1 in the cavity length direction. Here, a facet 17 at the light
reflecting side and a facet 16 at the light emitting side serving
as a light emitting portion of nitride semiconductor laser device
10 in the present embodiment can be formed, for example, as
follows: a wafer formed by stacking the aforementioned nitride
semiconductor layers such as a buffer layer in order on the
aforementioned semiconductor substrate, forming a ridge stripe
portion, and thereafter forming an insulating film, a p-electrode
and an n-electrode is cleaved by such technique as scribing and
breaking using a diamond point. The cleavage surfaces formed by
this cleavage are facet 16 and facet 17 parallel to each other as
shown in FIG. 2.
[0048] Then, an aluminum oxynitride film 31 having a thickness of 6
nm is formed as a first coat film on facet 16 at the light emitting
side, and an aluminum oxide film 32 having a thickness of 80 nm is
formed as a second coat film on aluminum oxynitride film 31, with
reflectivity of 7%.
[0049] On the other hand, an aluminum oxynitride film 33 having a
thickness of 6 nm is formed on facet 17 at the light reflecting
side. An aluminum oxide film 34 having a thickness of 80 nm is
formed on aluminum oxynitride film 33. A high reflection film 35
with reflectivity of 95% or higher is formed on aluminum oxide film
34 by stacking four pairs of a 71 nm-thick silicon oxide film and a
46 nm-thick titanium oxide film (stacked starting from the silicon
oxide film) and thereafter forming a silicon oxide film having a
thickness of 142 nm on the outermost surface.
[0050] Each of the aforementioned aluminum oxynitride film 31,
aluminum oxide film 32, aluminum oxynitride film 33, aluminum oxide
film 34, and high reflection film 35 may be formed for example by
ECR (Electron Cyclotron Resonance) sputtering as described below,
or may be formed by any other sputtering, EB (Electron Beam)
evaporation, CVD (Chemical Vapor Deposition), or the like.
[0051] FIG. 3 schematically shows a configuration of an exemplary
ECR sputtering apparatus. Here, an ECR sputtering apparatus 40 is
mainly formed of a deposition furnace 50 and a plasma generation
room 60. Deposition furnace 50 is provided with a gas inlet 51 and
a gas outlet 56. A target 52, a heater 53 for heating, a sample
stage 54, and a shutter 55 are installed in deposition furnace 50.
A sample 66 after cleavage as described above is placed on sample
stage 54. Here, sample 66 is attached to a holder (not shown) in
such a direction that allows a film to be deposited on facet 16 or
facet 17. A vacuum pump (not shown) is also attached to gas outlet
56 to allow gas in deposition furnace 50 to be discharged
therefrom. An RF power supply 57 is additionally connected to
target 52.
[0052] Furthermore, plasma generation room 60 is provided with a
gas inlet 61 and a microwave introduction port 62. A microwave
introduction window 63 and a magnetic coil 64 are installed in
plasma generation room 60. Then, a microwave 65 introduced from
microwave introduction port 62 is introduced through microwave
introduction window 63, so that plasma is generated from the gas
introduced from gas inlet 61.
[0053] Using ECR sputtering apparatus 40 having such a
configuration, as shown in FIG. 2, aluminum oxynitride film 31
having a thickness of 6 nm is first formed on facet 16 at the light
emitting side and then aluminum oxide film 32 having a thickness of
80 nm is successively formed on aluminum oxynitride film 31.
[0054] Specifically, first, nitrogen gas is introduced into
deposition furnace 50 at a flow rate of 5.5 sccm, oxygen gas is
introduced at a flow rate of 1.5 sccm, and argon gas is introduced
at a flow rate of 20.0 sccm in order to efficiently generate plasma
to increase the deposition rate. Then, RF power of 500 W is applied
to target 52 for sputtering target 52 made of aluminum and 500 W of
microwave power necessary for generating plasma is applied. Then,
aluminum oxynitride film 31 having an oxygen content of 20 atomic %
with refractive index of 2.1 for light having a wavelength of 405
nm can be formed at a deposition rate of 1.7 A/second. The
respective contents (atomic %) of aluminum, nitrogen and oxygen
included in aluminum oxynitride film 31 can be measured for example
by AES (Auger Electron Spectroscopy). TEM-EDX (Transmission
Electron Microscopy-Energy Dispersive X-ray Spectroscopy) is also
available.
[0055] Then, introduction of nitrogen gas is stopped, oxygen gas is
introduced at a flow rate of 6.6 sccm, and argon gas is introduced
at a flow rate of 40.0 sccm. RF power of 500 W is applied to target
52 for sputtering target 52 made of aluminum, and a microwave power
of 500 W necessary for generating plasma is applied. Thus, aluminum
oxide film 32 can be formed at a deposition rate of 3.0
A/second.
[0056] Before forming aluminum oxynitride film 31, an oxide film or
impurity attached on facet 16 is preferably removed for cleaning by
heating facet 16, for example, at a temperature of at least
100.degree. C. and at most 500.degree. C. in the deposition
apparatus. However, such cleaning may not be performed in the
present invention. Alternatively, facet 16 may be cleaned before
formation of aluminum oxynitride film 31 by irradiating facet 16
with argon or nitrogen plasma. However, such cleaning may not be
performed in the present invention. Plasma radiation may be applied
while facet 16 is heated before formation of aluminum oxynitride
film 31. As for the plasma radiation as described above, for
example, it is also possible to apply argon plasma and thereafter
successively apply nitrogen plasma. Plasma may be applied in the
reverse order. Other than argon and nitrogen, for example, such a
rare gas as helium, neon, xenon, or krypton may be used. Here,
aluminum oxynitride film 31 formed on facet 16 may also be formed
while being heated for example at a temperature of at least
100.degree. C. and at most 500.degree. C. However, in the present
invention, aluminum oxynitride film 31 may be formed without being
heated.
[0057] In the present invention, an oxide film formed on aluminum
oxynitride film 31 may be formed in a different method from a
method of forming the oxynitride film. For example, after aluminum
oxynitride film 31 is formed by ECR sputtering, aluminum oxide film
32 may be formed by EB (Electron Beam) evaporation or the like.
[0058] Thereafter, after formation of aluminum oxynitride film 31
and aluminum oxide film 32 as described above, aluminum oxynitride
film 33, aluminum oxide film 34 and high reflection film 35 are
formed in this order on facet 17 at the light reflecting side by
the above-noted ECR sputtering or the like. Preferably, before
formation of these films, cleaning by heating and/or cleaning by
plasma radiation are also performed.
[0059] Here, degradation is significant in the light emitting
portion which is a part of the facet at the light emitting side,
while degradation is often insignificant in the facet at the light
reflecting side where optical density is low as compared with the
light emitting side. Therefore, in the present invention, the
configuration of a film formed on the facet at the light reflecting
side is not limited, and a film may not be formed on the facet at
the light reflecting side.
[0060] Furthermore, a heating process may be performed after the
above-noted films are formed on the facet at the light emitting
side and the facet at the light reflecting side. Thus, removal of
moisture contained in the above-noted film and improvement in film
quality by the heating process can be expected. The heating process
may be performed by heating with a heater, ultraviolet laser
radiation, or the like.
[0061] In this manner, aluminum oxynitride film 31 and aluminum
oxide film 32 are formed in order on facet 16 at the light emitting
side of the aforementioned sample, and aluminum oxynitride film 33,
aluminum oxide film 34 and high reflection film 35 are formed in
order on facet 17 at the light reflecting side. The sample is
thereafter divided into chips, resulting in a nitride semiconductor
laser device.
[0062] Now, an aging test was conducted in such a manner that the
resultant nitride semiconductor laser device in this embodiment was
allowed to continuously emit laser light with an optical power of
100 mW with CW drive in a temperature environment of 70.degree. C.
The result is shown in FIG. 4. As shown in FIG. 4, as for the
nitride semiconductor laser device of the present embodiment, even
after 500 hours passed, all the seven nitride semiconductor laser
devices subjected to the aging test were driven without stopping
laser light emission.
[0063] For comparison, a nitride semiconductor laser device was
fabricated similarly to the present embodiment, except that the
respective thicknesses of aluminum oxide film 32 at the light
emitting side and aluminum oxide film 34 at the light reflecting
side are set at 40 nm. Then, an aging test was conducted for the
resultant nitride semiconductor laser device for comparison,
similarly to the nitride semiconductor laser device in the present
embodiment. The result is shown in FIG. 5. As shown in FIG. 5, for
the nitride semiconductor laser device for comparison, all the six
nitride semiconductor laser devices subjected to the aging test
stopped emission within 60 hours. The facets at the light emitting
side of these nitride semiconductor laser devices which stopped
emission were found to have holes which seemed to be created by
thermal melting.
[0064] In addition, for comparison, a nitride semiconductor laser
device was fabricated similarly to the present embodiment, except
that the respective thicknesses of aluminum oxynitride film 31 at
the light emitting side and aluminum oxynitride film 33 at the
light reflecting side are set at 3 nm.
[0065] Then, an aging test was conducted in such a manner that the
resultant nitride semiconductor laser device for comparison was
allowed to continuously emit low-power laser light with an optical
power of 65 mW with CW drive in a temperature environment of
70.degree. C. The result is shown in FIG. 6. As shown in FIG. 6,
for the nitride semiconductor laser device for comparison, all the
ten nitride semiconductor laser devices subjected to the aging test
were driven normally without stopping emission until 400 hours.
[0066] However, when an aging test was conducted in such a manner
that this nitride semiconductor laser device was allowed to
continuously emit high-power laser light with an optical power of
100 mW with CW drive in a temperature environment of 70.degree. C.,
as shown in FIG. 7, all the seven nitride semiconductor laser
devices subjected to the aging test stopped emission within 20
hours. The light emitting portions of these nitride semiconductor
laser devices which stopped emission were found to have holes which
seemed to be created by thermal melting.
[0067] On the other hand, for the nitride semiconductor laser
device in the present embodiment, after the aforementioned aging
test was conducted for 500 hours, degradation of the light emitting
portion was also examined. Here, no degradation was found.
[0068] Therefore, it was found that with CW drive and low power
with an optical power of about 65 mW, even if the thickness of
aluminum oxynitride film 31 at the light emitting side is as thin
as 3 nm, sufficient long-term reliability can be achieved, while
with CW drive and high power with an optical power of about 100 mW,
long-term reliability cannot be achieved.
[0069] Here, for the nitride semiconductor laser device for
comparison, long-term reliability is achieved in the aging test
with CW drive and low power drive with an optical power of 65 mW,
because the aluminum oxynitride film may function as an adhesion
layer and adhere well to the facet at the light emitting side.
However, at the time of high power drive with an optical power of
100 mW with CW drive, it is insufficient that the aluminum
oxynitride film merely functions as an adhesion layer.
[0070] Based on the foregoing, the thickness of aluminum oxynitride
film 31 is set at 6 nm and the thickness of the aluminum oxide film
is set at 80 nm, so that the likelihood of poor reliability
resulting from degradation of the light emitting portion can be
reduced at the time of high power drive, and long-term reliability
at the time of high power drive can be improved.
[0071] In other words, aluminum oxynitride film 31 and aluminum
oxide film 32 formed at the light emitting portion are made thick
enough, so that long-term reliability at the time of high power
drive can be achieved, which is insufficient when these films are
thin. Now, in order to determine a thickness necessary for
achieving long-term reliability at the time of high power drive, an
aging test was conducted with varied thicknesses of aluminum
oxynitride film 31 and aluminum oxide film 32.
[0072] FIG. 8 shows the relation between the thickness of aluminum
oxide film 32 and the proportion of nitride semiconductor laser
devices that were driven normally after 500 hours when they were
allowed to continuously emit high-power laser light with an optical
power of 100 mW with CW drive in a temperature environment of
70.degree. C., where the thickness of aluminum oxynitride film 31
formed on the facet at the light emitting side of the nitride
semiconductor laser device in the present embodiment is fixed at 6
nm and the thickness of aluminum oxide film 32 formed on aluminum
oxynitride film 31 is varied.
[0073] As shown in FIG. 8, it was found that in the case where the
thickness of aluminum oxynitride film 31 on the facet at the light
emitting side was 6 nm, if the thickness of aluminum oxide film 32
formed on aluminum oxynitride film 31 was 80 nm or thicker,
long-term reliability was achieved even at the time of high power
drive.
[0074] Next, the COD levels were compared, with the thicknesses of
aluminum oxide film 32 set at 80 nm, 160 nm and 240 nm, when
high-power laser light with an optical power of 100 mW was
continuously emitted for 500 hours with CW drive in a temperature
environment of 70.degree. C. As a result, the average COD level of
five nitride semiconductor laser devices for each thickness is as
follows. When the thickness of aluminum oxide film 32 was 80 nm,
the average COD level was 258 mW. When the thickness was 160 nm,
the average COD level was 340 mW. When the thickness was 240 nm,
the average COD level was 346 mW. Accordingly, it was determined
that the thickness of aluminum oxide film 32 was preferably 80 nm
or thicker and more preferably 160 nm or thicker.
[0075] Now, FIG. 9 shows the relation between the thickness of
aluminum oxynitride film 31 and the proportion of nitride
semiconductor laser devices that were driven normally after 500
hours when they were allowed to continuously emit high-power laser
light with an optical power of 100 mW with CW drive in a
temperature environment of 70.degree. C., where the thickness of
aluminum oxynitride film 31 on the facet at the light emitting side
of the nitride semiconductor laser device in the present embodiment
was varied and the thickness of aluminum oxide film 32 formed on
aluminum oxynitride film 31 was fixed at 80 nm.
[0076] As shown in FIG. 9, it was found that in the case where the
thickness of aluminum oxide film 32 on the facet at the light
emitting side was 80 nm, when the thickness of aluminum oxynitride
film 31 was set to 6 nm or thicker, long-term reliability was
achieved even at the time of high power drive.
[0077] Next, the COD levels were compared, with the thicknesses of
aluminum oxynitride film 31 set at 6 nm, 12 nm and 50 nm, when
high-power laser light with an optical power of 100 mW was
continuously emitted for 500 hours with CW drive in a temperature
environment of 70.degree. C. As a result, the average COD level of
five nitride semiconductor laser devices for each thickness is as
follows. When the thickness of aluminum oxynitride film 31 was 6
nm, the average COD level was 258 mW. When the thickness was 12 nm,
the average COD level was 356 mW. When the thickness was 50 nm, the
average COD level was 487 mW. Accordingly, it was determined that
the thickness of aluminum oxynitride film 31 was preferably 6 nm or
thicker, more preferably 12 nm or thicker, and even more preferably
50 nm or thicker.
[0078] In consideration of the foregoing results, it can be
understood that when the thickness of aluminum oxynitride film 31
is 6 nm or thicker and the thickness of aluminum oxide film 32
formed thereon is 80 nm or thicker, long-term reliability can be
achieved even at the time of high power drive without degradation
of the light emitting portion.
Second Embodiment
[0079] A nitride semiconductor laser device in the present
embodiment has the similar configuration as the nitride
semiconductor laser device in the first embodiment, except that the
respective configurations of films formed on the facets at the
light emitting side and the light reflecting side are changed and
that the wavelength of emitted laser light is set at 410 nm.
[0080] Here, in the nitride semiconductor laser device in the
present embodiment, respective aluminum nitride films each having a
thickness of 6 nm are formed on the facets at the light emitting
side and at the light reflecting side, and an aluminum oxide film
having a thickness of 80 nm is formed on each of the aluminum
nitride films. Here, the reflectivity at the light emitting side is
set to 7%. The aluminum nitride film and the aluminum oxide film
are formed by ECR sputtering. Specifically, deposition was
performed without introducing oxygen gas, which is introduced in
the first embodiment to form an aluminum oxynitride film. Besides,
the aluminum nitride film may be formed by a variety of sputtering,
MBE (Molecular Beam Epitaxy), or the like. On the facet at the
light reflecting side, a high reflection film having an identical
configuration to that of the first embodiment is formed on the
aluminum oxide film.
[0081] For the nitride semiconductor laser device in the present
embodiment, an aging test was conducted under the same method and
the same conditions as the first embodiment. The result is shown in
FIG. 10. As shown in FIG. 10, it was observed that all the fourteen
nitride semiconductor laser devices in the present embodiment
subjected to the aging test were driven without stopping laser
light emission, even after 200 hours passed, and it was found that
long-term reliability at the time of high power drive was
achieved.
Third Embodiment
[0082] A nitride semiconductor laser device in the present
embodiment has the similar configuration as the nitride
semiconductor laser device in the first embodiment, except that the
respective configurations of films formed on the facets at the
light emitting side and the light reflecting side are changed and
that the wavelength of emitted laser light is set at 400 nm.
[0083] Here, in the nitride semiconductor laser device in the
present embodiment, respective aluminum oxynitride films each
having a thickness of 12 nm are formed on the facets at the light
emitting side and at the light reflecting side, and an aluminum
oxide film having a thickness of 80 nm is formed on each of the
aluminum oxynitride films. Here, the reflectivity at the light
emitting side is set to 10%. On the facet at the light reflecting
side, a high reflection film having an identical configuration to
that of the first embodiment is formed on the aluminum oxide
film.
[0084] For the nitride semiconductor laser device in the present
embodiment, an aging test was conducted under the same method and
the same conditions as the first embodiment. The result is shown in
FIG. 11. As shown in FIG. 11, it was observed that all the five
nitride semiconductor laser devices in the present embodiment
subjected to the aging test were driven without stopping laser
light emission, even after 800 hours passed, and it was found that
long-term reliability at the time of high power drive was
achieved.
Fourth Embodiment
[0085] A nitride semiconductor laser device in the present
embodiment has the similar configuration as the nitride
semiconductor laser device in the first embodiment, except that the
respective configurations of films formed on the facets at the
light emitting side and the light reflecting side are changed and
that the wavelength of emitted laser light is set at 390 nm.
[0086] Here, in the nitride semiconductor laser device in the
present embodiment, respective aluminum oxynitride films each
having a thickness of 50 nm are formed on the facets at the light
emitting side and at the light reflecting side, and an aluminum
oxide film having a thickness of 160 nm is formed on each of the
aluminum oxynitride films. Here, the reflectivity at the light
emitting side is 6%. On the facet at the light reflecting side, a
high reflection film having an identical configuration to that of
the first embodiment is formed on the aluminum oxide film.
[0087] For the nitride semiconductor laser device in the present
embodiment, an aging test was conducted under the same method and
the same conditions as the first embodiment. The result is shown in
FIG. 12. As shown in FIG. 12, it was observed that all the eight
nitride semiconductor laser devices in the present embodiment
subjected to the aging test were driven without stopping laser
light emission, even after 1000 hours passed, and it was found that
long-term reliability at the time of high power drive could be
improved.
[0088] It is noted that although in the foregoing description,
reliability at the time of high power drive has been examined for a
nitride semiconductor laser device, the result similar to the
foregoing result can also be brought about when the first coat film
and the second coat film as described above are formed on a light
emitting surface as a light emitting portion of a nitride
semiconductor diode device.
Fifth Embodiment
[0089] A nitride semiconductor laser device in the present
embodiment has the similar configuration as the nitride
semiconductor laser device in the first embodiment, except that the
respective configurations of films formed on the facets at the
light emitting side and the light reflecting side are changed.
[0090] Here, in the nitride semiconductor laser device in the
present embodiment, an aluminum oxynitride film having a thickness
of 20 nm is formed on the facet at the light emitting side, and an
aluminum oxide film having a thickness of 150 nm is formed on the
aluminum oxynitride film. Here, the reflectivity of the film formed
on the facet at the light emitting side is 5%.
[0091] On the other hand, an aluminum oxynitride film having a
thickness of 20 nm is formed on the facet at the light reflecting
side, an aluminum oxynitride film having a thickness of 110 nm is
formed on the aluminum oxynitride film, and four pairs of a silicon
oxide film having a thickness of 71 nm and a titanium oxide film
having a thickness of 46 nm are stacked on the aluminum oxynitride
film (stacked starting from the silicon oxide film) and thereafter
a silicon oxide film having a thickness of 142 nm is formed on the
outermost surface. The reflectivity of the film formed on the facet
at the light reflecting side is 95% or higher.
[0092] Here, each of the aluminum oxynitride film and the aluminum
oxide film is formed by ECR sputtering. An aging test was conducted
similarly to the first embodiment in such a manner that the nitride
semiconductor laser device in the present embodiment was allowed to
continuously emit high-power laser light with an optical power of
100 mW with CW drive in a temperature environment of 70.degree. C.
The result is shown in FIG. 14. As shown in FIG. 14, it was
observed that all the four nitride semiconductor laser devices in
the present embodiment subjected to the aging test were driven
without stopping laser light emission even after 2500 hours passed,
and it was found that long-term reliability at the time of high
power drive can be achieved.
[0093] In addition, the COD level was measured when the nitride
semiconductor laser device in the present embodiment was allowed to
continuously emit high-power laser light with an optical power of
100 mW for 500 hours with CW drive in a temperature environment of
70.degree. C. As a result, the average COD level of five nitride
semiconductor laser devices was 338 mW.
[0094] As described in the first embodiment, when the thickness of
the aluminum oxide film on the aluminum oxynitride film on the
facet at the light emitting side is 80 nm, the average COD level is
258 mW, when it is 160 nm, the average COD level is 340 mW, and
when it is 240 nm, the average COD level is 346 mW. Therefore, it
can be said that when the thickness of the aluminum oxide film on
the aluminum oxynitride film on the facet at the light emitting
side is 150 nm or thicker, long-term reliability at the time of
high power drive can be improved greatly as compared with when it
is 80 nm.
Sixth Embodiment
[0095] A nitride semiconductor laser device in the present
embodiment has the similar configuration as the nitride
semiconductor laser device in the first embodiment, except that the
respective configurations of films formed on the facets at the
light emitting side and the light reflecting side are changed.
[0096] Here, in the nitride semiconductor laser device in the
present embodiment, an aluminum oxynitride film having a thickness
of 20 nm is formed on the facet at the light emitting side, and an
aluminum oxide film having a thickness of 130 nm is formed on the
aluminum oxynitride film. Here, the reflectivity of the film formed
on the facet at the light emitting side is 12.5%.
[0097] On the other hand, an aluminum oxynitride film having a
thickness of 20 nm is formed on the facet at the light reflecting
side, an aluminum oxynitride film having a thickness of 110 nm is
formed on the aluminum oxynitride film, and four pairs of a silicon
oxide film having a thickness of 71 nm and a titanium oxide film
having a thickness of 46 nm are stacked on the aluminum oxynitride
film (stacked starting from the silicon oxide film) and thereafter
a silicon oxide film having a thickness of 142 nm is formed on the
outermost surface. The reflectivity of the film formed on the facet
at the light reflecting side is 95% or higher.
[0098] Here, each of the aluminum oxynitride film and the aluminum
oxide film is formed by ECR sputtering.
[0099] An aging test was conducted similarly to the first
embodiment in such a manner that the nitride semiconductor laser
device in the present embodiment was allowed to continuously emit
high-power laser light with an optical power of 100 mW with CW
drive in a temperature environment of 70.degree. C. The result is
shown in FIG. 15. As shown in FIG. 15, it was observed that all the
eight nitride semiconductor laser devices in the present embodiment
subjected to the aging test were driven without stopping laser
light emission even after 1200 hours passed, and it was found that
long-term reliability at the time of high power drive can be
achieved.
[0100] In addition, the COD level was measured when the nitride
semiconductor laser device in the present embodiment was allowed to
continuously emit high-power laser light with an optical power of
100 mW for 500 hours with CW drive in a temperature environment of
70.degree. C. As a result, the average COD level of five nitride
semiconductor laser devices was 320 mW.
[0101] As described in the first embodiment, when the thickness of
the aluminum oxide film on the aluminum oxynitride film on the
facet at the light emitting side is 80 nm, the average COD level is
258 mW, when it is 130 nm, the average COD level is 338 mW, when it
is 160 nm, the average COD level is 340 mW, and when it is 240 nm,
the average COD level is 346 mW. Therefore, it can be said that
when the thickness of the aluminum oxide film on the aluminum
oxynitride film on the facet at the light emitting side is 130 nm
or thicker, long-term reliability at the time of high power drive
can be improved greatly as compared with when it is 80 nm.
[0102] The present invention is applicable, for example, to a
nitride semiconductor laser device emitting light having a
wavelength in the ultraviolet to green region and a broad area type
nitride semiconductor laser device for use in illumination with a
stripe width of a few tens of pm.
[0103] Although the present invention has been described and
illustrated in detail, it is clearly understood that the same is by
way of illustration and example only and is not to be taken by way
of limitation, the spirit and scope of the present invention being
limited only by the terms of the appended claims.
* * * * *