U.S. patent application number 13/040798 was filed with the patent office on 2011-08-18 for nitride based semiconductor laser device.
This patent application is currently assigned to SANYO ELECTRIC CO., LTD.. Invention is credited to Masayuki HATA, Ryoji HIROYAMA, Shingo KAMEYAMA, Yasuhiko NOMURA.
Application Number | 20110200065 13/040798 |
Document ID | / |
Family ID | 40508249 |
Filed Date | 2011-08-18 |
United States Patent
Application |
20110200065 |
Kind Code |
A1 |
KAMEYAMA; Shingo ; et
al. |
August 18, 2011 |
NITRIDE BASED SEMICONDUCTOR LASER DEVICE
Abstract
One facet and the other facet of a nitride based semiconductor
laser device are respectively composed of a cleavage plane of
(0001) and a cleavage plane of (000 1). Thus, the one facet and the
other facet are respectively a Ga polar plane and an N polar plane.
A portion of the one facet and a portion of the other facet, which
are positioned in an optical waveguide, constitute a pair of cavity
facets. A first protective film including oxygen as a constituent
element is formed on the one facet. A second protective film
including nitrogen as a constituent element is formed on the other
facet.
Inventors: |
KAMEYAMA; Shingo; (Osaka,
JP) ; NOMURA; Yasuhiko; (Osaka, JP) ;
HIROYAMA; Ryoji; (Kyoto, JP) ; HATA; Masayuki;
(Osaka, JP) |
Assignee: |
SANYO ELECTRIC CO., LTD.
Moriguchi-City
JP
|
Family ID: |
40508249 |
Appl. No.: |
13/040798 |
Filed: |
March 4, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12236627 |
Sep 24, 2008 |
7924898 |
|
|
13040798 |
|
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Current U.S.
Class: |
372/49.01 |
Current CPC
Class: |
H01S 5/0287 20130101;
H01S 5/32341 20130101; H01S 5/1082 20130101; H01S 5/320225
20190801; H01S 5/0282 20130101; H01S 5/2201 20130101; H01S 2301/176
20130101; H01S 5/227 20130101 |
Class at
Publication: |
372/49.01 |
International
Class: |
H01S 5/028 20060101
H01S005/028 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 28, 2007 |
JP |
2007-253413 |
Sep 18, 2008 |
JP |
2008-240084 |
Claims
1. A nitride based semiconductor laser device comprising: a nitride
based semiconductor layer having an optical waveguide extending in
a substantial [0001] direction and having one facet composed of a
substantial (0001) plane and the other facet composed of a
substantial (0001) plane as a pair of cavity facets; a first
protective film provided on said one facet and including oxygen as
a constituent element; and a second protective film provided on
said other facet and including nitrogen as a constituent element,
wherein an intensity of laser light emitted from said other facet
is higher than an intensity of laser light emitted from said one
facet.
2-5. (canceled)
6. The nitride based semiconductor laser device according to claim
1, wherein said first protective film further includes nitrogen as
a constituent element, and an oxygen composition ratio is higher
than a nitrogen composition ratio in said first protective
film.
7. (canceled)
8. The nitride based semiconductor laser device according to claim
1, wherein said second protective film further includes oxygen as a
constituent element, and the nitrogen composition ratio is higher
than the oxygen composition ratio in said second protective
film.
9-10. (canceled)
11. The nitride based semiconductor laser device according to claim
1, further comprising a dielectric multilayer film formed on said
one facet and including said first protective film, wherein said
dielectric multilayer film includes a first oxide film, an
oxynitride film, and a second oxide film that are laminated in this
order from said one facet, the nitrogen composition ratio is higher
than the oxygen composition ratio in said oxynitride film, and said
first protective film is said first oxide film.
12. (canceled)
13. The nitride based semiconductor laser device according to claim
1, further comprising a dielectric multilayer film formed on said
other facet and including said second protective film, wherein said
dielectric multilayer film includes a nitride film and an oxide
film that are laminated in this order from said other facet, and
said second protective film is said nitride film.
14. The nitride based semiconductor laser device according to claim
1, further comprising a dielectric multilayer film formed on said
other facet and including said second protective film, wherein said
dielectric multilayer film includes a first nitride film, an oxide
film, and a second nitride film that are laminated in this order
from said other facet, and said second protective film is said
first nitride film.
15. The nitride based semiconductor laser device according to claim
1, further comprising a dielectric multilayer film formed on said
other facet and including said second protective film, wherein said
dielectric multilayer film includes an oxynitride film and an oxide
film that are laminated in this order from said other facet, the
nitrogen composition ratio is higher than the oxygen composition
ratio in said oxynitride film, and said second protective film is
said oxynitride film.
16. The nitride based semiconductor laser device according to claim
1, further comprising a dielectric multilayer film formed on said
other facet and including said second protective film, wherein said
dielectric multilayer film includes a nitride film, an oxynitride
film, and an oxide film that are laminated in this order from said
other facet, the nitrogen composition ratio is higher than the
oxygen composition ratio in said oxynitride film, and said second
protective film is said nitride film.
17. The nitride based semiconductor laser device according to claim
1, further comprising a dielectric multilayer film formed on said
other facet and including said second protective film, wherein said
dielectric multilayer film includes a first oxynitride film, a
second oxynitride film, and an oxide film that are laminated in
this order from said other facet, the nitrogen composition ratio is
higher than the oxygen composition ratio in said first oxynitride
film, the oxygen composition ratio is higher than the nitrogen
composition ratio in said second oxynitride film, and said second
protective film is said first oxynitride film.
18. The nitride based semiconductor laser device according to claim
6, wherein said first protective film includes at least one of
AlO.sub.XN.sub.Y, SiO.sub.XN.sub.Y and TaO.sub.XN.sub.Y, where
X>Y.
19. The nitride based semiconductor laser device according to claim
1, wherein said second protective film includes at least one of AlN
and Si.sub.3N.sub.4.
20. The nitride based semiconductor laser device according to claim
8, wherein said second protective film includes at least one of
AlO.sub.XN.sub.Y, SiO.sub.XN.sub.Y and TaO.sub.XN.sub.Y, where
X<Y.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a nitride based
semiconductor laser device having a nitride based semiconductor
layer.
[0003] 2. Description of the Background Art
[0004] In recent years, nitride-based semiconductor laser devices
have been utilized as light sources for next-generation
large-capacity disks and have been actively developed.
[0005] In such nitride-based semiconductor laser devices, the plane
directions of main surfaces of active layers are taken as
substantial (H, K, --H--K, 0) planes such as (11 20) planes or (1
100) planes, so that piezoelectric fields generated in the active
layers can be reduced. As a result, it is known that the luminous
efficiency of laser light can be improved. Here, H and K, described
above, are any integers, and at least one of H and K is an integer
other than zero.
[0006] Furthermore, it has been known that the gains of the nitride
based semiconductor laser devices can be improved by setting the
(0001) planes and the (000 1) planes to pairs of cavity facets
(see, for example, JP 8-213692 A and Japanese Journal of Applied
Physics Vol. 46, No. 9, 2007, pp. L187.about.L189).
[0007] In the above-mentioned nitride based semiconductor laser
devices, however, protective films formed on the cavity facets are
easily stripped.
SUMMARY OF THE INVENTION
[0008] According to an aspect of the present invention, a nitride
based semiconductor laser device includes a nitride based
semiconductor layer having an optical waveguide extending in a
substantial [0001] direction and having one facet composed of a
substantial (0001) plane and the other facet composed of a
substantial (000 1) plane as a pair of cavity facets, a first
protective film provided on the one facet and including oxygen as a
constituent element, and a second protective film provided on the
other facet and including nitrogen as a constituent element.
[0009] The intensity of the laser light emitted from the one facet
may be higher than the intensity of the laser light emitted from
the other facet.
[0010] Each of a portion of the one facet and a portion of the
other facet in the optical waveguide may have unevenness, and the
depth of a first recess in the one facet may be smaller than the
depth of a second recess in the other facet.
[0011] The intensity of the laser light emitted from the other
facet may be higher than the intensity of the laser light emitted
from the one facet.
[0012] The first protective film may include no nitrogen as a
constituent element. Alternatively, the first protective film may
further include nitrogen as a constituent element, and the oxygen
composition ratio may be higher than the nitrogen composition ratio
in the first protective film.
[0013] The second protective film may include no oxygen as a
constituent element. Alternatively, the second protective film may
further include oxygen as a constituent element, and the nitrogen
composition ratio may be higher than the oxygen composition ratio
in the second protective film.
[0014] The nitride based semiconductor laser device may further
include a dielectric multilayer film formed on the one facet and
including the first protective film, in which the dielectric
multilayer film may include a first oxide film and a second oxide
film that are laminated in this order from the one facet, and the
first protective film may be the first oxide film.
[0015] The nitride based semiconductor laser device may further
include a dielectric multilayer film formed on the one facet and
including the first protective film, in which the dielectric
multilayer film may include an oxynitride film and an oxide film
that are laminated in this order from the one facet, the oxygen
composition ratio may be higher than the nitrogen composition ratio
in the oxynitride film, and the first protective film may be the
oxynitride film.
[0016] The nitride based semiconductor laser device may further
include a dielectric multilayer film formed on the one facet and
including the first protective film, in which the dielectric
multilayer film may include a first oxide film, an oxynitride film,
and a second oxide film that are laminated in this order from the
one facet, the nitrogen composition ratio may be higher than the
oxygen composition ratio in the oxynitride film, and the first
protective film may be the first oxide film.
[0017] The nitride based semiconductor laser device may further
include a dielectric multilayer film formed on the one facet and
including the first protective film, in which the dielectric
multilayer film may include a first oxynitride film, a second
oxynitride film, and an oxide film that are laminated in this order
from the one facet, the oxygen composition ratio may be higher than
the nitrogen composition ratio in the first oxynitride film, the
nitrogen composition ratio may be higher than the oxygen
composition ratio in the second oxynitride film, and the first
protective film may be the first oxynitride film.
[0018] The nitride based semiconductor laser device may include a
dielectric multilayer film formed on the other facet and including
the second protective film, in which the dielectric multilayer film
may include a nitride film and an oxide film that are laminated in
this order from the other facet, and the second protective film may
be the nitride film.
[0019] The nitride based semiconductor laser device may further
include a dielectric multilayer film formed on the other facet and
including the second protective film, in which the dielectric
multilayer film may include a first nitride film, an oxide film,
and a second nitride film that are laminated in this order from the
other facet, and the second protective film may be the first
nitride film.
[0020] The nitride based semiconductor laser device may further
include a dielectric multilayer film formed on the other facet and
including the second protective film, in which the dielectric
multilayer film may include an oxynitride film and an oxide film
that are laminated in this order from the other facet, the nitrogen
composition ratio may be higher than the oxygen composition ratio
in the oxynitride film, and the second protective film may be the
oxynitride film.
[0021] The nitride based semiconductor laser device may further
include a dielectric multilayer film formed on the other facet and
including the second protective film, in which the dielectric
multilayer film may include a nitride film, an oxynitride film, and
an oxide film that are laminated in this order from the other
facet, the nitrogen composition ratio may be higher than the oxygen
composition ratio in the oxynitride film, and the second protective
film may be the nitride film.
[0022] The nitride based semiconductor laser device may further
include a dielectric multilayer film formed on the other facet and
including the second protective film, in which the dielectric
multilayer film may include a first oxynitride film, a second
oxynitride film, and an oxide film that are laminated in this order
from the other facet, the nitrogen composition ratio may be higher
than the oxygen composition ratio in the first oxynitride film, the
oxygen composition ratio may be higher than the nitrogen
composition ratio in the second oxynitride film, and the second
protective film may be the first oxynitride film.
[0023] The first protective film may include at least one of
AlO.sub.XN.sub.Y, SiO.sub.XN.sub.Y and TaO.sub.XN.sub.Y, where
X>Y.
[0024] The second protective film may include at least one of AlN
and Si.sub.3N.sub.4.
[0025] The second protective film may include at least one of
AlO.sub.XN.sub.Y, SiO.sub.XN.sub.Y and TaO.sub.XN.sub.Y, where
X<Y.
[0026] Other features, elements, characteristics, and advantages of
the present invention will become more apparent from the following
description of preferred embodiments of the present invention with
reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a vertical sectional view of a nitride based
semiconductor laser device according to a first embodiment;
[0028] FIG. 2 is a vertical sectional view of a nitride based
semiconductor laser device according to a first embodiment;
[0029] FIG. 3 is a partially enlarged sectional view of the nitride
based semiconductor laser device shown in FIG. 2;
[0030] FIG. 4 is a partially enlarged sectional view of the nitride
based semiconductor laser device shown in FIG. 2;
[0031] FIG. 5 is a vertical sectional view of a nitride based
semiconductor laser device according to a second embodiment;
[0032] FIG. 6 is a vertical sectional view of a nitride based
semiconductor laser device according to a third embodiment;
[0033] FIG. 7 is a vertical sectional view of a nitride based
semiconductor laser device according to a fourth embodiment;
[0034] FIG. 8 is a vertical sectional view of a nitride based
semiconductor laser device according to a fifth embodiment;
[0035] FIG. 9 is a vertical sectional view of a nitride based
semiconductor laser device according to a sixth embodiment;
[0036] FIG. 10 is a vertical sectional view of a nitride based
semiconductor laser device according to a seventh embodiment;
and
[0037] FIG. 11 is a vertical sectional view of a nitride based
semiconductor laser device according to an eighth embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
1. First Embodiment
[0038] (1) Configuration of Nitride Based Semiconductor Laser
Device
[0039] FIGS. 1 and 2 are vertical sectional views of a nitride
based semiconductor laser device according to a first embodiment. A
line A1-A1 shown in FIG. 1 represents a position in longitudinal
section, and a line A2-A2 shown in FIG. 2 represents a position in
longitudinal section.
[0040] As shown in FIGS. 1 and 2, a nitride based semiconductor
laser device 1 according to the present embodiment includes an
n-type GaN substrate 101 having a thickness of approximately 100
.mu.m in which Si (silicon) has been doped. The carrier
concentration of the substrate 101 is approximately
5.times.10.sup.18 cm.sup.-3.
[0041] The substrate 101 is an off substrate having a crystal
growth plane inclined at approximately 0.3 degrees in a [000 1]
direction from a (11 20) plane. As shown in FIG. 1, a pair of steps
ST extending in a [0001] direction is formed on an upper surface of
the substrate 101. The pair of steps ST is positioned on both sides
of the substrate 101. The depth of each of the steps ST is
approximately 0.5 .mu.m, and the width thereof is approximately 20
.mu.m.
[0042] An n-type layer 102 having a thickness of approximately 100
nm in which Si has been doped is formed on the upper surface of the
substrate 101. The n-type layer 102 is composed of n-type GaN, and
the amount of doping of Si into the n-type layer 102 is
approximately 5.times.10.sup.18 cm.sup.-3.
[0043] An n-type cladding layer 103 composed of n-type
Al.sub.0.07Ga.sub.0.93N having a thickness of approximately 400 nm
in which Si has been doped is formed on the n-type layer 102. The
amount of doping of Si into the n-type cladding layer 103 is
approximately 5.times.10.sup.18 cm.sup.-3, and the carrier
concentration of the n-type cladding layer 103 is approximately
5.times.10.sup.18 cm.sup.-3.
[0044] An n-type carrier blocking layer 104 composed of n-type
Al.sub.0.16Ga.sub.0.84N having a thickness of approximately 5 nm in
which Si has been doped is formed on the n-type cladding layer 103.
The amount of doping of Si into the n-type carrier blocking layer
104 is approximately 5.times.10.sup.18 cm.sup.-3, and the carrier
concentration of the n-type carrier blocking layer 104 is
approximately 5.times.10.sup.18 cm.sup.-3.
[0045] An n-type optical guide layer 105 composed of n-type GaN
having a thickness of approximately 100 nm in which Si has been
doped is formed on the n-type carrier blocking layer 104. The
amount of doping of Si into the n-type optical guide layer 105 is
approximately 5.times.10.sup.18 cm.sup.-3, and the carrier
concentration of the n-type optical guide layer 105 is
approximately 5.times.10.sup.18 cm.sup.-3.
[0046] An active layer 106 is formed on the n-type optical guide
layer 105. The active layer 106 has an MQW (Multi-Quantum Well)
structure in which four barrier layers 106a (see FIG. 3, described
later) composed of undoped In.sub.0.02Ga.sub.0.98N having a
thickness of approximately 20 nm and three well layers 106b (see
FIG. 3, described later) composed of undoped In.sub.0.6Ga.sub.0.4N
having a thickness of approximately 3 nm are alternately
laminated.
[0047] A P-type optical guide layer 107 composed of p-type GaN
having a thickness of approximately 100 nm in which Mg (magnesium)
has been doped is formed on the active layer 106. The amount of
doping of Mg into the p-type optical guide layer 107 is
approximately 4.times.10.sup.19 cm.sup.-3, and the carrier
concentration of the p-type optical guide layer 107 is
approximately 5.times.10.sup.17 cm.sup.-3.
[0048] An n-type cap layer 108 composed of p-type
Al.sub.0.16Ga.sub.0.84N having a thickness of approximately 20 nm
in which Mg has been doped is formed on the p-type optical guide
layer 107. The amount of doping of Mg into the p-type cap layer 108
is approximately 4.times.10.sup.19 cm.sup.-3, and the carrier
concentration of the p-type cap layer 108 is approximately
5.times.10.sup.17 cm.sup.-3.
[0049] A p-type cladding layer 109 composed of p-type
Al.sub.0.07Ga.sub.0.93N in which Mg has been doped is formed on the
p-type cap layer 108. The amount of doping of Mg into the p-type
cladding layer 109 is approximately 4.times.10.sup.19 cm.sup.-3,
and the carrier concentration of the p-type cap layer 108 is
approximately 5.times.10.sup.17 cm.sup.-3.
[0050] Here, the p-type cladding layer 109 includes a flat portion
109b formed on the p-type cap layer 108 and a projection 109a
extending in the [0001] direction on the center of the flat portion
109b.
[0051] The thickness of the flat portion 109b in the p-type
cladding layer 109 is approximately 80 nm, and the height from an
upper surface of the flat portion 109b to an upper surface of the
projection 109a is approximately 320 nm. Furthermore, the width of
the projection 109a is approximately 1.75 .mu.m.
[0052] A p-type contact layer 110 composed of p-type
In.sub.0.02Ga.sub.0.98N having a thickness of approximately 10 nm
in which Mg has been doped is formed on the projection 109a in the
p-type cladding layer 109. The amount of doping of Mg into the
p-type contact layer 110 is approximately 4.times.10.sup.19
cm.sup.-3, and the carrier concentration of the p-type contact
layer 110 is approximately 5.times.10.sup.17 cm.sup.-3.
[0053] The projection 109a in the p-type cladding layer 109 and the
p-type contact layer 110 constitute a ridge Ri. Thus, an optical
waveguide WG along the [0001] direction is formed in a portion
below the ridge Ri and including the active layer 106.
[0054] An ohmic electrode 111 is formed on the p-type contact layer
110. The ohmic electrode 111 has a structure in which Pt
(platinum), Pd (palladium), and Au (gold) are laminated in this
order. The thicknesses of Pt, Pd, and Au are 5 nm, 100 nm, and 150
nm, respectively.
[0055] A current narrowing layer 112 composed of an insulating film
having a thickness of approximately 250 nm covers the upper surface
of the flat portion 109b, an upper surface of the n-type cladding
layer 103, and side surfaces of the above-mentioned layers 103 to
111. In this example, an SiO.sub.2 (silicon oxide) film is used as
an insulating film.
[0056] A pad electrode 113 is formed in respective predetermined
regions of an upper surface of the ohmic electrode 111 and a side
surface and an upper surface of the current narrowing layer 112.
The pad electrode 113 has a structure in which Ti (titanium), Pd,
and Au are laminated in this order. The thicknesses of Ti, Pd, and
Au are approximately 100 nm, approximately 100 nm, and
approximately 3 .mu.m, respectively.
[0057] Furthermore, an n-side electrode 114 is formed on a back
surface of the substrate 101. The n-side electrode 114 has a
structure in which Al (aluminum), Pt, and Au are laminated in this
order. The thicknesses of Al, Pt, andAu are respectively 10 nm, 20
nm, and 300 nm.
[0058] The n-type cladding layer 103, the n-type carrier blocking
layer 104, the n-type optical guide layer 105, the active layer
106, the p-type optical guide layer 107, the p-type cap layer 108,
the p-type cladding layer 109, and the p-type contact layer 110
constitute a nitride based semiconductor layer.
[0059] Here, out of paired cavity facets of the nitride based
semiconductor laser device 1, the cavity facet having the lower
reflective index and the cavity facet having the higher reflective
index are respectively referred to as a light emission facet and a
rear facet.
[0060] As shown in FIG. 2, a light emission facet 1F and a rear
facet 1B of the nitride based semiconductor laser device 1 are
respectively composed of a cleavage plane of (0001) and a cleavage
plane of (000 1). Thus, the light emission facet 1F and the rear
facet 1B are respectively a Ga (gallium) polar plane and an N
(nitrogen) polar plane. A portion of the light emission facet 1F
positioned in the optical waveguide WG and a portion of the rear
facet 1B positioned in the optical waveguide WG constitute a pair
of cavity facets.
[0061] A first dielectric multilayer film 210 is formed on the
light emission facet 1F of the nitride based semiconductor laser
device 1. The first dielectric multilayer film 210 has a structure
in which an Al.sub.2O.sub.3 film 211 and an SiO.sub.2 film 212 are
laminated in this order. Thus, the Al.sub.2O.sub.3 film 211 serving
as an oxide film functions as a protective film of the light
emission facet 1F.
[0062] The thicknesses of the Al.sub.2O.sub.3 film 211 and the
SiO.sub.2 film 212 are approximately 120 nm and approximately 42
nm, respectively. The reflective index of the first dielectric
multilayer film 210 is approximately 8%.
[0063] On the other hand, a second dielectric multilayer film 220
is formed on the rear facet 1B of the nitride based semiconductor
laser device 1. The second dielectric multilayer film 220 has a
structure in which an AlN film 221, a reflective film 222, and an
AlN film 223 are laminated in this order. Thus, the AlN film 221
serving as a nitride film functions as a protective film of the
rear facet 1B.
[0064] The respective thicknesses of the AlN films 221 and 223 are
10 nm. The reflective film 222 has a ten-layer structure in which
five SiO.sub.2 films having a thickness of approximately 70 nm and
five TiO.sub.2 films having a thickness of approximately 45 nm are
alternately laminated. The SiO.sub.2 film is used as a low
refractive index film, and the TiO.sub.2 film is used as a high
refractive index film. The reflective index of the second
dielectric multilayer film 220 is approximately 95%.
[0065] A voltage is applied between the pad electrode 113 and the
n-side electrode 114 in the nitride based semiconductor laser
device 1, so that laser light is respectively emitted from the
light emission facet 1F and the rear facet 1B.
[0066] In the present embodiment, the first dielectric multilayer
film 210 having a reflective index of approximately 8% is provided
on the light emission facet 1F, and the second dielectric
multilayer film 220 having a reflective index of approximately 95%
is provided on the rear facet 1B, as described above. Thus, the
intensity of the laser light emitted from the light emission facet
1F is significantly higher than the intensity of the laser light
emitted from the rear facet 1B. That is, the light emission facet
1F is a principal emission facet of the laser light.
[0067] (2) Details of Light Emission Facet 1F and Rear Facet 1B
[0068] FIGS. 3 and 4 are partially enlarged sectional views of the
nitride based semiconductor laser device 1 shown in FIG. 2. FIG. 3
is an enlarged sectional view of the light emission facet 1F and
its vicinity in the optical waveguide WG, and FIG. 4 is an enlarged
sectional view of the rear facet 1B and its vicinity in the optical
waveguide WG.
[0069] As shown in FIGS. 3 and 4, the active layer 106 has a
structure in which the four barrier layers 106a and the three well
layers 106b are alternately laminated. In the light emission facet
1F and the rear facet 1B, the well layers 106b in the active layer
106 project outward farther than the other layers in the nitride
based semiconductor laser. Therefore, a portion of the active layer
106 in each of the light emission facet 1F and the rear facet 1B
has unevenness formed by recesses and projections formed
therein.
[0070] The depth D1 (FIG. 3) of the recesses of the active layer
106 in the light emission facet 1F of the nitride based
semiconductor laser device 1 is approximately 1 nm, while the depth
D2 (FIG. 4) of the recesses of the active layer 106 in the rear
facet 1B thereof is approximately 6 nm. Note that the thinner one
of the high refractive index film (TiO.sub.2 film) and the low
refractive index film (SiO.sub.2 film), i.e., the TiO.sub.2 film in
this example, in the reflective film 222 is adjusted to a thickness
larger than the depth D2 of the recesses of the active layer 106 in
the rear facet 1B. In this case, the second dielectric multilayer
film 220 can be easily formed so as to reliably cover the recesses
and projections of the active layer 106 in the rear facet 1B. This
makes it possible to ensure a high reflective index of the second
dielectric multilayer film 220.
[0071] The reason why the active layer 106 has the recesses and
projections formed therein is as follows. When the nitride based
semiconductor laser device 1 is manufactured, the light emission
facet 1F and the rear facet 1B are cleaned, as described later. In
the cleaning process, the light emission facet 1F and the rear
facet 1B are irradiated with ECR (Electron Cyclotron Resonance)
plasma. Thus, the light emission facet 1F and the rear facet 1B are
etched.
[0072] Here, the composition of the well layers 106a in the active
layer 106 differs from the respective compositions of the other
layers, in the nitride based semiconductor layer, such as the
barrier layers 106a, the n-type optical guide layer 105, and the
p-type optical guide layer 107. Therefore, a difference occurs
between the etching amount of the well layer 106b in the active
layer 106 and the etching amount of the other layer in the nitride
based semiconductor layer. Therefore, the recesses and projections
are formed in the portion of the active layer 106 in each of the
light emission facet 1F and the rear facet 1B.
[0073] The higher the In composition ratio in the well layer 106b
composed of undoped In.sub.xGa.sub.1-xN is, the more significant
the recesses and projections become. This is caused by the
difference between the composition of the well layer 106b and the
composition of the other layer being greater when the In
composition ratio is higher than the Ga composition ratio in the
well layer 106 (0.5<x.ltoreq.1). In the present embodiment, the
In composition ratio x in the well layer 106b is 0.6.
[0074] Particularly, the (000 1) plane of the nitride based
semiconductor layer is chemically stabler than the (0001) plane
thereof. Therefore, the difference in the etching amount between
the well layer 106b and the other layer in the (000 1) plane is
greater than the difference in the etching amount between the well
layer 106b and the other layer in the (0001) plane. Thus, the depth
D2 of the recesses in the rear facet 1B is larger than the depth D1
of the recesses in the light emission facet 1F.
[0075] The larger the depth of recesses in a cavity facet having a
concavo-convex shape is, the more greatly laser light is scattered
due to the concavo-convex shape. In the present embodiment, the
light emission facet 1F is composed of the (0001) plane having few
recesses and projections. This can inhibit the laser light from
being scattered on the light emission facet 1F. As a result, a
preferable far field pattern having few ripples can be obtained at
the time of lasing.
[0076] (3) Method for Manufacturing Nitride Based Semiconductor
Laser Device 1
[0077] A method for manufacturing the nitride based semiconductor
laser device 1 having the above-mentioned configuration will be
described.
[0078] First, a substrate 101 having a plurality of grooves G (see
FIG. 1) extending in a [0001] direction formed on its upper surface
is first prepared. The depth of the groove G is approximately 0.5
.mu.m, and the width thereof is approximately 40 .mu.m. A distance
between the adjacent two grooves G is approximately 400 .mu.m. Note
that the groove G is previously formed in order to make the device
into chips in later processes. A part of the groove G constitutes
the above-mentioned step ST.
[0079] An n-type layer 102 having a thickness of approximately 100
nm, an n-type cladding layer 103 having a thickness of
approximately 400 nm, an n-type carrier blocking layer 104 having a
thickness of approximately 5 nm, an n-type optical guide layer 105
having a thickness of approximately 100 nm, an active layer 106
having a thickness of approximately 90 nm, a p-type optical guide
layer 107 having a thickness of approximately 100 nm, a p-type cap
layer 108 having a thickness of approximately 20 nm, a p-type
cladding layer 109 having a thickness of approximately 400 nm, and
a p-type contact layer 110 having a thickness of approximately 10
nm are sequentially formed on an upper surface of the substrate 101
by metal organic vapor phase epitaxy (MOVPE), for example.
[0080] Note that the thickness of the active layer 106 represents
the total thickness of four barrier layers 106a and three well
layers 106b.
[0081] Thereafter, annealing for changing into a p type and
formation of a ridge Ri shown in FIG. 1 are performed. An ohmic
electrode 111, a current narrowing layer 112, and a pad electrode
113 are formed. Furthermore, an n-side electrode 114 is formed on a
back surface of the substrate 101.
[0082] Then, a cavity facet (a light emission facet 1F and a rear
facet 1B) is formed, and a first dielectric multilayer film 210 and
a second dielectric multilayer film 220 are formed on the cavity
facet, as described later.
[0083] Scribe flaws extending in a (1 100) direction are formed on
the substrate 101 on which the layers 102 to 110, the ohmic
electrode 111, the current narrowing layer 112, and the pad
electrode 113 are formed. The scribe flaws are formed in a
broken-line shape in a portion excluding the ridge Ri by laser
scribing or mechanical scribing.
[0084] Then, the substrate 101 is cleaved such that the light
emission facet 1F and the rear facet 1B are formed. Thus, the
substrate 101 is separated into sticks.
[0085] Therefore, the separated substrate 101 is introduced into an
ECR sputter film formation device.
[0086] The light emission facet 1F obtained by the cleavage is
irradiated with plasma for five minutes. Note that the plasma is
generated under conditions of a microwave power of 500 W in a
N.sub.2 gas atmosphere of approximately 0.02 Pa. Thus, the light
emission facet 1F is cleaned while being slightly etched. In this
case, no RF power (high-frequency power) is applied to a sputter
target. Thereafter, the first dielectric multilayer film 210 (see
FIG. 2) is formed on the light emission facet 1F by ECR
sputtering.
[0087] Similarly, the rear facet 1B obtained by the cleavage is
irradiated with plasma for five minutes. Thus, the rear facet 1B is
cleaned while being slightly etched. In the case, no RF power is
applied to a sputter target. Thereafter, the second dielectric
multilayer film 220 (see FIG. 2) is formed on the rear facet 1B by
ECR sputtering.
[0088] Thus cleaning the light emission facet 1F and the rear facet
1B by the ECR plasma inhibits the degradation of the cavity facet
and the occurrence of optical breakdown of the cavity facet. This
allows the laser characteristics of the nitride based semiconductor
laser device 1 to be improved.
[0089] Thereafter, the stick-shaped substrate 101 is separated into
chips at the center of the groove G formed on the substrate 101.
Thus, the nitride based semiconductor laser device 1 shown in FIG.
1 is completed.
2. Second Embodiment
[0090] As to a nitride based semiconductor laser device according
to a second embodiment, the difference from the nitride based
semiconductor laser device 1 according to the first embodiment will
be described.
[0091] FIG. 5 is a vertical sectional view of the nitride based
semiconductor laser device according to the second embodiment. In
FIG. 5, a vertical section of the nitride based semiconductor laser
device 1 along a [0001] direction is shown, similarly to the
vertical section shown in FIG. 2 in the first embodiment. A
vertical section taken along a line A2-A2 shown in FIG. 5 is the
same as the vertical section of the nitride based semiconductor
laser device 1 shown in FIG. 1.
[0092] A first dielectric multilayer film 210 is formed on a light
emission facet 1F of the nitride based semiconductor laser device
1. The first dielectric multilayer film 210 has a structure in
which an AlO.sub.XN.sub.Y film (X>Y) 211a and an Al.sub.2O.sub.3
film 212a are laminated in this order. Here, the refractive index
of the AlO.sub.XN.sub.Y film 211a is approximately 1.7. The
AlO.sub.XN.sub.Y film 211a serving as an oxynitride film in which
the oxygen composition ratio is higher than the nitrogen
composition ratio functions as a protective film of the light
emission facet 1F.
[0093] The thicknesses of the AlO.sub.XN.sub.Y film 211a and the
Al.sub.2O.sub.3 film 212a are approximately 30 nm and approximately
57 nm, respectively. The reflective index of the first dielectric
multilayer film 210 is approximately 8%.
[0094] On the other hand, a second dielectric multilayer film 220
is formed on a rear facet 1B of the nitride based semiconductor
laser device 1. The second dielectric multilayer film 220 has a
structure in which an AlO.sub.XN.sub.Y film (X<Y) 221a and a
reflective film 222a are laminated in this order. The refractive
index of the AlO.sub.XN.sub.Y film 221a is approximately 1.9. The
AlO.sub.XN.sub.Y film 221a serving as an oxynitride film in which
the nitrogen composition ratio is higher than the oxygen
composition ratio functions as a protective film of the rear facet
1B.
[0095] The thickness of the AlO.sub.XN.sub.Y film 221a is
approximately 30 nm. The reflective film 222a has a ten-layer
structure in which five SiO.sub.2 films having a thickness of
approximately 70 nm and five TiO.sub.2 films having a thickness of
approximately 45 nm are alternately laminated. The SiO.sub.2 film
is used as a low refractive index film, and the TiO.sub.2 film is
used as a high refractive index film. The reflective index of the
second dielectric multilayer film 220 is approximately 95%.
3. Third Embodiment
[0096] As to a nitride based semiconductor laser device according
to a third embodiment, the difference from the nitride based
semiconductor laser device 1 according to the first embodiment will
be described.
[0097] FIG. 6 is a vertical sectional view of the nitride based
semiconductor laser device according to the third embodiment. In
FIG. 6, a vertical section of the nitride based semiconductor laser
device 1 along a [0001] direction is shown, similarly to the
vertical section shown in FIG. 2 in the first embodiment. A
vertical section taken along a line A2-A2 shown in FIG. 6 is the
same as the vertical section of the nitride based semiconductor
laser device 1 shown in FIG. 1.
[0098] A first dielectric multilayer film 210 is formed on a light
emission facet 1F of the nitride based semiconductor laser device
1. The first dielectric multilayer film 210 has a structure in
which an Al.sub.2O.sub.3 film 211b, an AlO.sub.XN.sub.Y film
(X<Y) 212b, and an Al.sub.2O.sub.3 film 213b are laminated in
this order. The refractive index of the AlO.sub.XN.sub.Y film 212b
is approximately 1.9. The Al.sub.2O.sub.3 film 211b serving as an
oxide film functions as a protective film of the light emission
facet 1F.
[0099] The thicknesses of the Al.sub.2O.sub.3 film 211b, the
AlO.sub.XN.sub.Y film 212b, and the Al.sub.2O.sub.3 film 213a are
approximately 10 nm, approximately 30 nm, and approximately 52 nm,
respectively. The reflective index of the first dielectric
multilayer film 210 is approximately 8%.
[0100] On the other hand, a second dielectric multilayer film 220
is formed on a rear facet 1B of the nitride based semiconductor
laser device 1. The second dielectric multilayer film 220 has a
structure in which an AlN film 221b, an AlO.sub.XN.sub.Y film
(X<Y) 222b, an Al.sub.2O.sub.3 film 223b, and a reflective film
224b are laminated in this order. The refractive index of the
AlO.sub.xN.sub.y film 222b is approximately 1.9. The AlN film 221b
serving as a nitride film functions as a protective film of the
rear facet 1B.
[0101] The thicknesses of the AlN film 221b, the AlO.sub.XN.sub.Y
film 222b, and the Al.sub.2O.sub.3 film 223b are approximately 10
nm, approximately 30 nm, and approximately 60 nm, respectively. The
reflective film 224b has a ten-layer structure in which five
SiO.sub.2 films having a thickness of approximately 70 nm and five
TiO.sub.2 films having a thickness of approximately 45 nm are
alternately laminated. The SiO.sub.2 film is used as a low
refractive index film, and the TiO.sub.2 film is used as a high
refractive index film. The reflective index of the second
dielectric multilayer film 220 is approximately 95%.
4. Fourth Embodiment
[0102] As to a nitride based semiconductor laser device according
to a fourth embodiment, the difference from the nitride based
semiconductor laser device 1 according to the first embodiment will
be described.
[0103] FIG. 7 is a vertical sectional view of the nitride based
semiconductor laser device according to the fourth embodiment. In
FIG. 7, a vertical section of the nitride based semiconductor laser
device 1 along a [0001] direction is shown, similarly to the
vertical section shown in FIG. 2 in the first embodiment. A
vertical section taken along a line A2-A2 shown in FIG. 7 is the
same as the vertical section of the nitride based semiconductor
laser device 1 shown in FIG. 1.
[0104] A first dielectric multilayer film 210 is formed on a light
emission facet 1F of the nitride based semiconductor laser device
1. The first dielectric multilayer film 210 has a structure in
which an AlO.sub.XN.sub.Y film (X>Y) 211c, an AlO.sub.XN.sub.Y
film (X<Y) 212c, and an Al.sub.2O.sub.3 film 213c are laminated
in this order. The refractive indexes of the AlO.sub.XN.sub.Y film
211c and the AlO.sub.XN.sub.Y film 212c are approximately 1.7 and
approximately 1.9, respectively. The AlO.sub.XN.sub.Y film 211c
serving as an oxynitride film in which the oxygen composition ratio
is higher than the nitrogen composition ratio functions as a
protective film of the light emission facet 1F.
[0105] The thicknesses of the AlO.sub.XN.sub.Y film 211c, the
AlO.sub.XN.sub.Y film 212c, and the Al.sub.2O.sub.3 film 213c are
approximately 30 nm, approximately 30 nm, and approximately 15 nm,
respectively. The reflective index of the first dielectric
multilayer film 210 is approximately 8%.
[0106] On the other hand, a second dielectric multilayer film 220
is formed on a rear facet 18 of the nitride based semiconductor
laser device 1. The second dielectric multilayer film 220 has a
structure in which an AlO.sub.XN.sub.Y film (X<Y) 221c, an
AlO.sub.XN.sub.Y film (X>Y) 222c, and a reflective film 223c are
laminated in this order. The refractive indexes of the
AlO.sub.XN.sub.Y film 221c and the AlO.sub.XN.sub.Y film 222c are
approximately 1.9 and approximately 1.7, respectively. The
AlO.sub.XN.sub.Y film 221c serving as an oxynitride film in which
the nitrogen composition ratio is higher than the oxygen
composition ratio functions as a protective film of the rear facet
1B.
[0107] The thicknesses of the AlO.sub.XN.sub.Y film (X<Y) 221c
and the AlO.sub.XN.sub.Y film (X>Y) 222c are approximately 30 nm
and approximately 30 nm, respectively. The reflective film 223c has
a ten-layer structure in which five SiO.sub.2 films having a
thickness of approximately 70 nm and five TiO.sub.2 films having a
thickness of approximately 45 nm are alternately laminated. The
SiO.sub.2 film is used as a low refractive index film, and the
TiO.sub.2 film is used as a high refractive index film. The
reflective index of the second dielectric multilayer film 220 is
approximately 95%.
5. Correspondences Between Elements in Claims and Parts in
Embodiments
[0108] In the following two paragraphs, non-limiting examples of
correspondences between various elements recited in the claims
below and those described above with respect to various preferred
embodiments of the present invention are explained.
[0109] In the first to fourth embodiments described above, the
optical waveguide WG is an example of an optical waveguide
extending in a substantial [0001] direction, the light emission
facet 1F is an example of one facet composed of a substantial
(0001) plane, and the rear facet 1B is an example of the other
facet composed of a substantial (000 1) plane.
[0110] Furthermore, the light emission facet 1F and the rear facet
1B are examples of a cavity facet, and the nitride based
semiconductor layer including the n-type cladding layer 103, the
n-type carrier blocking layer 104, the n-type optical guide layer
105, the active layer 106, the p-type optical guide layer 107, the
p-type cap layer 108, the p-type cladding layer 109, and the p-type
contact layer 110 is an example of a nitride based semiconductor
layer.
[0111] In the first embodiment, the Al.sub.2O.sub.3 film 211 is an
example of a first protective film including oxygen as a
constituent element, and the AlN film 221 is an example of a second
protective film including nitrogen as a constituent element. In the
second embodiment, the AlO.sub.XN.sub.Y film (X>Y) 211a is an
example of a first protective film including oxygen as a
constituent element, and the AlO.sub.XN.sub.Y film (X<Y) 221a is
an example of a second protective film including nitrogen as a
constituent element. In the third embodiment, the Al.sub.2O.sub.3
film 211b is an example of a first protective film including oxygen
as a constituent element, and the AlN film 221b is an example of a
second protective film including nitrogen as a constituent element.
In the fourth embodiment, the AlO.sub.XN.sub.Y film (X>Y) 211c
is an example of a first protective film including oxygen as a
constituent element, and the AlO.sub.XN.sub.Y film (X<Y) 221c is
an example of a second protective film including nitrogen as a
constituent element.
[0112] In the first embodiment, the Al.sub.2O.sub.3 film 211 and
the SiO.sub.2 film 212 in the first dielectric multilayer film 210
are respectively examples of a first oxide film and a second oxide
film. In the second embodiment, the AlO.sub.XN.sub.Y film (X>Y)
211a and the Al.sub.2O.sub.3 film 212a in the first dielectric
multilayer film 210 are respectively examples of an oxynitride film
and an oxide film. In the third embodiment, the Al.sub.2O.sub.3
film 211b, the AlO.sub.XN.sub.Y film (X<Y) 212b, and the
Al.sub.2O.sub.3 film 212b in the first dielectric multilayer film
210 are respectively examples of a first oxide film, an oxynitride
film, and a second oxide film. In the fourth embodiment, the
AlO.sub.XN.sub.Y film (X>Y) 211c, the AlO.sub.XN.sub.Y film
(X<Y) 212c, and the Al.sub.2O.sub.3 film 213c in the first
dielectric multilayer film 210 are respectively examples of a first
oxynitride film, a second oxynitride film, and an oxide film.
[0113] As each of constituent elements recited in the claims,
various other elements having configurations or functions described
in the claims can be also used.
6. Effects of First to Fourth Embodiments
[0114] (a)
[0115] In the nitride based semiconductor laser devices according
to the first to fourth embodiments, one facet composed of a
substantial (0001) plane and the other facet composed of a
substantial (000 1) plane constitute a pair of cavity facets of an
optical waveguide extending in a substantial [0001] direction, and
laser light is respectively emitted from the one facet and the
other facet.
[0116] The one facet composed of the substantial (0001) plane is
easily covered with a Group 13 element such as gallium because it
is a Group 13 element polar plane. The one facet is provided with a
first protective film including oxygen as a constituent element.
This causes binding of the Group 13 element and an oxygen element
to be formed in the interface between the one facet and the first
protective film. Here, binding energy between the Group 13 element
and the oxygen element is significantly higher than binding energy
between a nitrogen element and the oxygen element.
[0117] In a case where the first protective film includes oxygen as
a constituent element, therefore, stripping of the first protective
film from the one facet can be more sufficiently prevented, as
compared with that in a case where it includes nitrogen as a
constituent element.
[0118] On the other hand, the other facet composed of the
substantial (000 1) plane is easily covered with nitrogen atoms
because it is a nitrogen polar plane. The other facet is provided
with a second protective film including nitrogen as a constituent
element. Since the second protective film thus includes nitrogen
that covers the other facet as a constituent element, adhesion
between the other facet and the second protective film is
enhanced.
[0119] This sufficiently prevents the first protective film from
being stripped from the one facet while sufficiently preventing the
second protective film from being stripped from the other facet.
Therefore, the reliability of the nitride based semiconductor laser
device is improved.
[0120] Furthermore, the intensity of the laser light emitted from
the one facet is higher than the intensity of the laser light
emitted from the other facet.
[0121] In this case, the one facet composed of the substantial
(0001) plane is taken as a principal light emission facet. Here,
the one facet is chemically stabler, as compared with the other
facet composed of the substantial (000 1) plane. This makes it more
difficult for the substantial (0001) plane to have recesses and
projections formed therein, as compared with the substantial (000
1) plane at the time of manufacturing, thereby making it difficult
for the laser light to be scattered on the one facet. Therefore, a
preferable far field pattern having few ripples can be efficiently
obtained.
[0122] Each of a portion of the one facet and a portion of the
other facet in the optical waveguide has recesses and projections,
and the depth of the recesses in the one facet is smaller than the
depth of the recesses in the other facet.
[0123] In this case, the laser light is difficult to scatter on the
one facet. Therefore, a preferable far field pattern having few
ripples can be efficiently obtained from the one facet.
[0124] (b) Effect of Protective Film Covering Light Emission Facet
1F and Rear Facet 1B
[0125] As described in the foregoing, the light emission facet 1F
and the rear facet 1B of the nitride based semiconductor laser
device 1 are respectively composed of a cleavage plane of (0001)
and a cleavage plane of (000 1). Thus, the light emission facet 1F
and the rear facet 1B are respectively a Ga polar plane and an N
polar plane.
[0126] In the first embodiment, the light emission facet 1F is
easily covered with Ga atoms because it is a Ga polar plane. The
Al.sub.2O.sub.3 film 211 serving as an oxide film is formed on the
light emission facet 1F. This causes binding of a Ga atom and an O
atom to be formed in the interface between the light emission facet
1F and the Al.sub.2O.sub.3 film 211.
[0127] Binding energy between a Ga atom and an O atom is
significantly higher than binding energy between an 0 atom and an N
atom. In a case where the Al.sub.2O.sub.3 film 211 serving as an
oxide film is formed on the light emission facet 1F, therefore,
stripping of the Al.sub.2O.sub.3 film 211 from the light emission
facet 1F is more sufficiently prevented, as compared with that in a
case where the nitride film is formed on the light emission facet
1F.
[0128] On the other hand, the rear facet 1B composed of the (000 1)
plane is easily covered with N atoms because it is a nitrogen polar
plane. The AlN film 221 serving as a nitride film is formed on the
rear facet 1B. Since the AlN film 221 thus includes N atoms
covering the rear facet 1B, therefore, adhesion between the rear
facet 1B and the AlN film 221 is enhanced. This sufficiently
prevents the AlN film 221 from being stripped from the rear facet
1B. Therefore, the reliability of the nitride based semiconductor
laser device 1 is improved.
[0129] In the second embodiment, the AlO.sub.XN.sub.Y film (X>Y)
211a serving as an oxide film in which the oxygen composition ratio
is higher than the nitrogen composition ratio is formed on the
light emission facet 1F composed of the (0001) plane. This
sufficiently prevents the AlO.sub.XN.sub.Y film (X>Y) 211a from
being stripped from the light emission facet 1F. Furthermore, the
AlO.sub.XN.sub.Y film (X<Y) 221a serving as a nitride film in
which the nitrogen composition ratio is higher than the oxygen
composition ratio is formed on the rear facet 1B composed of the
(000 1) plane. This sufficiently prevents the AlO.sub.XN.sub.Y film
(X<Y) 221a from being stripped from the rear facet 1B.
[0130] In the third embodiment, the Al.sub.2O.sub.3 film 211b
serving as an oxide film is formed on the light emission facet 1F
composed of the (0001) plane. This sufficiently prevents the
Al.sub.2O.sub.3 film 211b from being stripped from the light
emission facet 1F. Furthermore, the AlN film 221b serving as a
nitride film is formed on the rear facet 1B composed of the (000 1)
plane. This sufficiently prevents the AlN film 221b from being
stripped from the rear facet 1B.
[0131] In the fourth embodiment, the AlO.sub.XN.sub.Y film (X>Y)
211c serving as an oxide film in which the oxygen composition ratio
is higher than the nitrogen composition ratio is formed on the
light emission facet 1F composed of the (0001) plane. This
sufficiently prevents the AlO.sub.XN.sub.Y film (X>Y) 211c from
being stripped from the light emission facet 1F. Furthermore, the
AlO.sub.XN.sub.Y film (X<Y) 221c serving as a nitride film in
which the nitrogen composition ratio is higher than the oxygen
composition ratio is formed on the rear facet 1B composed of the
(000 1) plane. This sufficiently prevents the AlO.sub.XN.sub.Y film
(X<Y) 221c from being stripped from the rear facet 1B.
[0132] (c) Effect of Taking (0001) Plane as Light Emission Facet
1F
[0133] In the present embodiment, the (0001) plane is taken as the
light emission facet 1F, so that the depth of the recesses in the
light emission facet 1F is smaller than the depth of the recesses
in the rear facet 1B. This can inhibit the laser light from being
scattered on the light emission facet 1F. As a result, a preferable
far field pattern having few ripples can be obtained when the
nitride based semiconductor laser device 1 is operated.
[0134] Furthermore, the second dielectric multilayer film 220
having a high reflective index is formed on the rear facet 1B. Even
if a part of the laser light is scattered by the recesses and
projections in the rear facet 1B, therefore, the reduction in the
reflection amount is less affected by the scattering. This inhibits
a power of the laser light from being reduced.
7. Fifth Embodiment
[0135] (1) Configuration of Nitride Based Semiconductor Laser
Device
[0136] As to a nitride based semiconductor laser device according
to a fifth embodiment, the difference from the nitride based
semiconductor laser device 1 according to the first embodiment will
be described.
[0137] FIG. 8 is a vertical sectional view of the nitride based
semiconductor laser device according to the fifth embodiment. In
FIG. 8, a vertical section of the nitride based semiconductor laser
device 1 along a [0001] direction is shown, similarly to the
vertical section shown in FIG. 2 in the first embodiment. A
vertical section taken along a line A2-A2 shown in FIG. 8 is the
same as the vertical section of the nitride based semiconductor
laser device 1 shown in FIG. 1.
[0138] As shown in FIG. 8, a light emission facet 1Fa and a rear
facet 1Ba of the nitride based semiconductor laser device 1 are
respectively composed of a cleavage plane of (000 1) and a cleavage
plane of (0001).
[0139] A third dielectric multilayer film 230 is formed on the
light emission facet 1Fa. The third dielectric multilayer film 230
has a structure in which an AlN film 231, an Al.sub.2O.sub.3 film
232, and an AlN film 233 are laminated in this order. Thus, the AlN
film 231 serving as a nitride film functions as a protective film
of the light emission facet 1Fa.
[0140] The thicknesses of the AlN film 231, the Al.sub.2O.sub.3
film 232, and the AlN film 233 are approximately 10 nm,
approximately 85 nm, and approximately 10 nm, respectively. The
reflective index of the third dielectric multilayer film 230 is
approximately 5%.
[0141] A fourth dielectric multilayer film 240 is formed on the
rear facet 1Ba. The fourth dielectric multilayer film 240 has a
structure in which an Al.sub.2O.sub.3 film 241, a reflective film
242, and an AlN film 243 are laminated in this order. Thus, the
Al.sub.2O.sub.3 film 241 serving as an oxide film functions as a
protective film of the rear facet 1Ba.
[0142] The thickness of the Al.sub.2O.sub.3 film 241 is 120 nm. The
reflective film 242 has a ten-layer structure in which five
SiO.sub.2 films having a thickness of approximately 70 nm and five
TiO.sub.2 films having a thickness of approximately 45 nm are
alternately laminated. The SiO.sub.2 film is used as a low
refractive index film, and the TiO.sub.2 film is used as a high
refractive index film. The thickness of the AlN film 243 is 10 nm.
The reflective index of the fourth dielectric multilayer film 290
is approximately 95%.
[0143] In the nitride based semiconductor laser device 1 thus
formed, a voltage is applied between a pad electrode 113 and an
n-side electrode 114, so that laser light is respectively emitted
from the light emission facet 1Fa and the rear facet 1Ba.
[0144] In the present embodiment, the third dielectric multilayer
film 230 having a reflective index of approximately 5% is provided
on the light emission facet 1Fa, and the fourth dielectric
multilayer film 240 having a reflective index of approximately 95%
is provided on the rear facet 1Ba, as described above. This causes
the intensity of the laser light emitted from the light emission
facet 1Fa to be higher than the intensity of the laser light
emitted from the rear facet 1Ba. That is, the light emission facet
1Fa is a principal emission facet of the laser light.
[0145] Here, in the present embodiment, undoped
In.sub.0.02Ga.sub.0.98N is used as a barrier layer 106a in an
active layer 106, and undoped In.sub.0.15Ga.sub.0.85N is used as a
well layer 106b in the active layer 106.
[0146] Thus, in the nitride based semiconductor laser device 1
according to the present embodiment, the In composition ratio in
the well layer 106b is 0.15, and is significantly lower than the Ga
composition ratio. This sufficiently inhibits the recesses and
projections of the active layer 106 from becoming significant in
each of the light emission facet 1Fa and the rear facet 1Ba.
[0147] (2) Method for Manufacturing Nitride Based Semiconductor
Laser Device 1
[0148] As to a method for manufacturing the nitride based
semiconductor laser device 1 having the above-mentioned
configuration, the difference from that in the above-mentioned
first embodiment will be described.
[0149] When the nitride based semiconductor laser device 1
according to the present embodiment is manufactured, a substrate
101 on which an n-type layer 102, an n-type cladding layer 103, an
n-type carrier blocking layer 109, an n-type optical guide layer
105, an active layer 106, a p-type optical guide layer 107, a
p-type cap layer 108, a p-type cladding layer 109, and a p-type
contact layer 110 are formed is cleaved such that a light emission
facet 1Fa composed of a (000 1) plane and a rear facet 1Ba composed
of a (0001) plane are formed.
[0150] Thereafter, a third dielectric multilayer film 230 is formed
on the cleaned light emission facet 1Fa by ECR sputtering.
Furthermore, a fourth dielectric multilayer film 240 is formed on
the cleaned rear facet 1Ba by ECR sputtering.
[0151] Thereafter, the stick-shaped substrate 101 is separated into
chips at the center of a groove G formed on the substrate 101.
Thus, the nitride based semiconductor laser device 1 according to
the fifth embodiment shown in FIG. 8 is completed.
8. Sixth Embodiment
[0152] As to a nitride based semiconductor laser device according
to a sixth embodiment, the difference from the nitride based
semiconductor laser device 1 according to the fifth embodiment will
be described.
[0153] FIG. 9 is a vertical sectional view of the nitride based
semiconductor laser device according to the sixth embodiment. In
FIG. 9, a vertical section of the nitride based semiconductor laser
device 1 along a [0001] direction is shown, similarly to the
vertical section shown in FIG. 2 in the first embodiment. A
vertical section taken along a line A2-A2 shown in FIG. 9 is the
same as the vertical section of the nitride based semiconductor
laser device 1 shown in FIG. 1.
[0154] A third dielectric multilayer film 230 is formed on a light
emission facet 1Fa. The third dielectric multilayer film 230 has a
structure in which an AlO.sub.XN.sub.Y film (X<Y) 231a and an
Al.sub.2O.sub.3 film 232a are laminated in this order. The
refractive index of the AlO.sub.XN.sub.Y film 231a is approximately
1.9. The AlO.sub.XN.sub.Y film 231a serving as an oxynitride film
in which the nitrogen composition ratio is higher than the oxygen
composition ratio functions as a protective film of the light
emission facet 1Fa.
[0155] The thicknesses of the AlO.sub.XN.sub.Y film 231a and the
Al.sub.2O.sub.3 film 232a are approximately 30 nm and approximately
65 nm, respectively. The reflective index of the third dielectric
multilayer film 230 is approximately 8%.
[0156] A fourth dielectric multilayer film 240 is formed on a rear
facet 1Ba. The fourth dielectric multilayer film 240 has a
structure in which an AlO.sub.XN.sub.Y (X>Y) 241a and a
reflective film 242a are laminated in this order. The refractive
index of the AlO.sub.XN.sub.Y film 241a is approximately 1.7. The
AlO.sub.XN.sub.Y film 241a serving as an oxynitride film in which
the oxygen composition ratio is higher than the nitrogen
composition ratio functions as a protective film of the rear facet
1Ba.
[0157] The thickness of the AlO.sub.XN.sub.Y film 241a is
approximately 30 nm. The reflective film 242a has a ten-layer
structure in which five SiO.sub.2 films having a thickness of
approximately 70 nm and five TiO.sub.2 films having a thickness of
approximately 45 nm are alternately laminated. The SiO.sub.2 film
is used as a low refractive index film, and the TiO.sub.2 film is
used as a high refractive index film. The reflective index of the
fourth dielectric multilayer film 290 is approximately 95%.
9. Seventh Embodiment
[0158] As to a nitride based semiconductor laser device according
to a seventh embodiment, the difference from the nitride based
semiconductor laser device according to the fifth embodiment will
be described.
[0159] FIG. 10 is a vertical sectional view of the nitride based
semiconductor laser device according to the seventh embodiment. In
FIG. 10, a vertical section of the nitride based semiconductor
laser device 1 along a [0001] direction is shown, similarly to the
vertical section shown in FIG. 2 in the first embodiment. A
vertical section taken along a line A2-A2 shown in FIG. 10 is the
same as the vertical section of the nitride based semiconductor
laser device 1 shown in FIG. 1.
[0160] A third dielectric multilayer film 230 is formed on a light
emission facet 1Fa. The third dielectric multilayer film 230 has a
structure in which an AlN film 231b, an AlO.sub.XN.sub.Y film
(X<Y) 232b, and an Al.sub.2O.sub.3 film 233b are laminated in
this order. The refractive index of the AlO.sub.XN.sub.Y film 231b
is approximately 1.9. The AlN film 231b serving as a nitride film
functions as a protective film of the light emission facet 1Fa.
[0161] The thicknesses of the AlN film 231b, the AlO.sub.XN.sub.Y
film 232b, and the Al.sub.2O.sub.3 film 233b are approximately 10
nm, approximately 30 nm, and approximately 62 nm, respectively. The
reflective index of the third dielectric multilayer film 230 is
approximately 8%.
[0162] A fourth dielectric multilayer film 240 is formed on a rear
facet 1Ba. The fourth dielectric multilayer film 240 has a
structure in which an Al.sub.2O.sub.3 film 241b, an
AlO.sub.XN.sub.Y film (X<Y) 242b, an Al.sub.2O.sub.3 film 243b,
and a reflective film 244b are laminated in this order. The
refractive index of the AlO.sub.XN.sub.Y film 242b is approximately
1.9. The Al.sub.2O.sub.3 film 241b serving as an oxide film
functions as a protective film of the rear facet 1Ba.
[0163] The thicknesses of the Al.sub.2O.sub.3 film 241b, the
AlO.sub.XN.sub.Y film 242b, and the Al.sub.2O.sub.3 film 243b are
approximately 60 nm, approximately 30 nm, and approximately 60 nm,
respectively. The reflective film 244b has a ten-layer structure in
which five SiO.sub.2 films having a thickness of approximately 70
nm and five TiO.sub.2 films having a thickness of approximately 45
nm are alternately laminated. The SiO.sub.2 film is used as a low
refractive index film, and the TiO.sub.2 film is used as a high
refractive index film. The reflective index of the fourth
dielectric multilayer film 240 is approximately 95%.
10. Eighth Embodiment
[0164] As to a nitride based semiconductor laser device according
to an eighth embodiment, the difference from the nitride based
semiconductor laser device 1 according to the fifth embodiment will
be described.
[0165] FIG. 11 is a vertical sectional view of the nitride based
semiconductor laser device according to the eighth embodiment. In
FIG. 11, a vertical section of a nitride based semiconductor laser
device 1 along a [001] direction is shown, similarly to the
vertical section shown in FIG. 2 in the first embodiment. A
vertical section taken along a line A2-A2 shown in FIG. 11 is the
same as the vertical section of the nitride based semiconductor
laser device 1 shown in FIG. 1.
[0166] A third dielectric multilayer film 230 is formed on a light
emission facet 1Fa. The third dielectric multilayer film 230 has a
structure in which an AlO.sub.XN.sub.Y film (X<Y) 231c, an
AlO.sub.XN.sub.Y film (X>Y) 232c, and an Al.sub.2O.sub.3 film
233c are laminated in this order. The refractive indexes of the
AlO.sub.XN.sub.Y film 231c and the AlO.sub.XN.sub.Y film 232c are
approximately 1.9 and approximately 1.7, respectively. The
AlO.sub.XN.sub.Y film (X<Y) 231c serving as an oxynitride film
in which the nitrogen composition ratio is higher than the oxygen
composition ratio functions as a protective film of the light
emission facet 1Fa.
[0167] The thicknesses of the AlO.sub.XN.sub.Y film 231c, the
AlO.sub.XN.sub.Y film 232c, and the Al.sub.2O.sub.3 film 233c are
approximately 30 nm, approximately 30 nm, and approximately 35 nm,
respectively. The reflective index of the third dielectric
multilayer film 230 is approximately 8%.
[0168] A fourth dielectric multilayer film 240 is formed on a rear
facet 1Ba. The fourth dielectric multilayer film 240 has a
structure in which an AlO.sub.XN.sub.Y film (X.sub.>Y) 241c, an
AlO.sub.XN.sub.Y film (X<Y) 242c, and a reflective film 243c are
laminated in this order. The refractive indexes of the
AlO.sub.XN.sub.Y film 241c and the AlO.sub.XN.sub.Y film 242c are
approximately 1.7 and approximately 1.9, respectively. The
AlO.sub.XN.sub.Y film 241c serving as an oxynitride film in which
the oxygen composition ratio is higher than the nitrogen
composition ratio functions as a protective film of the rear facet
1Ba.
[0169] The thicknesses of the AlO.sub.XN.sub.Y film 241c and the
AlO.sub.XN.sub.Y film 242c are approximately 30 nm and
approximately 30 nm, respectively. The reflective film 243c has a
ten-layer structure in which five SiO.sub.2 films having a
thickness of approximately 70 nm and five TiO.sub.2 films having a
thickness of approximately 45 nm are alternately laminated. The
SiO.sub.2 film is used as a low refractive index film, and the
TiO.sub.2 film is used as a high refractive index film. The
reflective index of the fourth dielectric multilayer film 240 is
approximately 95%.
11. Correspondences Between Elements in Claims and Parts in
Embodiments
[0170] In the following two paragraphs, non-limiting examples of
correspondences between various elements recited in the claims
below and those described above with respect to various preferred
embodiments of the present invention are explained.
[0171] In the fifth to eighth embodiments described above, the
optical waveguide WG is an example of an optical waveguide
extending in a substantial [0001] direction, the rear facet 1Ba is
an example of one facet composed of a substantial (0001) plane, and
the light emission facet 1Fa is an example of the other facet
composed of a substantial (000 1) plane.
[0172] Furthermore, the light emission facet 1Fa and the rear facet
1Ba are examples of a cavity facet, and the nitride based
semiconductor layer including the n-type cladding layer 103, the
n-type carrier blocking layer 104, the n-type optical guide layer
105, the active layer 106, the p-type optical guide layer 107, the
p-type cap layer 108, the p-type cladding layer 109, and the p-type
contact layer 110 is an example of a nitride based semiconductor
layer.
[0173] In the fifth embodiment, the AlN film 231 is an example of a
second protective film including nitrogen as a constituent element,
and the Al.sub.2O.sub.3 film 241 is an example of a first
protective film including oxygen as a constituent element. In the
sixth embodiment, the AlO.sub.XN.sub.Y film (X<Y) 231a is an
example of a second protective film including nitrogen as a
constituent element, and the AlO.sub.XN.sub.Y film (X>Y) 241a is
an example of a first protective film including oxygen as a
constituent element. In the seventh embodiment, the AlN film 231b
is an example of a second protective film including nitrogen as a
constituent element, and the Al.sub.2O.sub.3 film 241b is an
example of a first protective film including oxygen as a
constituent element. In the eighth embodiment, the AlO.sub.XN.sub.Y
film (X<Y) 231c is an example of a second protective film
including nitrogen as a constituent element, and the
AlO.sub.XN.sub.Y film (X>Y) 241c is an example of a first
protective film including oxygen as a constituent element.
[0174] In the fifth embodiment, the AlN film 231, the
Al.sub.2O.sub.3 film 232, and the AlN film 233 in the third
dielectric multilayer film 230 are respectively examples of a first
nitride film (nitride film), an oxide film, and a second nitride
film. In the sixth embodiment, the AlO.sub.XN.sub.Y film (X<Y)
231a and the Al.sub.2O.sub.3 film 232a in the third dielectric
multilayer film 230 are respectively examples of an oxynitride film
and an oxide film. In the seventh embodiment, the AlN film 231b,
the AlO.sub.XN.sub.Y film (X<Y) 232b, and the Al.sub.2O.sub.3
film 233b in the third dielectric multilayer film 230 are
respectively examples of a nitride film, an oxynitride film, and an
oxide film. In the eighth embodiment, the AlO.sub.XN.sub.Y film
(X<Y) 231c, the AlO.sub.XN.sub.Y film (X>Y) 232c, and the
Al.sub.2O.sub.3 film 233c are respectively examples of a first
oxynitride film, a second oxynitride film, and an oxide film.
[0175] As each of constituent elements recited in the claims,
various other elements having configurations or functions described
in the claims can be also used.
12.Effects of Fifth to Eighth Embodiments
[0176] (a)
[0177] In the nitride based semiconductor laser devices according
to the fifth to eighth embodiments, one facet composed of a
substantial (0001) plane and the other facet composed of a
substantial (000 1) plane constitute a pair of cavity facets of an
optical waveguide extending in a substantial [0001] direction, and
laser light is respectively emitted from the one facet and the
other facet.
[0178] The one facet composed of the substantial (0001) plane is
easily covered with a Group 13 element such as gallium because it
is a Group 13 element polar plane. The one facet is provided with a
first protective film including oxygen as a constituent element.
This causes binding of the Group 13 element and an oxygen element
to be formed in the interface between the one facet and the first
protective film. Here, binding energy between the Group 13 element
and the oxygen element is significantly higher than binding energy
between a nitrogen element and the oxygen element.
[0179] In a case where the first protective film includes oxygen as
a constituent element, therefore, stripping of the first protective
film from the one facet can be more sufficiently prevented, as
compared with that in a case where it includes nitrogen as a
constituent element.
[0180] On the other hand, the other facet composed of the
substantial (000 1) plane is easily covered with nitrogen atoms
because it is a nitrogen polar plane. The other facet is provided
with a second protective film including nitrogen as a constituent
element. Since the second protective film thus includes nitrogen
that covers the other facet as a constituent element, adhesion
between the other facet and the second protective film is
enhanced.
[0181] This sufficiently prevents the first protective film from
being stripped from the one facet while sufficiently preventing the
second protective film from being stripped from the other facet.
Therefore, the reliability of the nitride based semiconductor laser
device is improved.
[0182] Furthermore, the intensity of the laser light emitted from
the other facet is higher than the intensity of the laser light
emitted from the one facet.
[0183] In this case, the other facet composed of the substantial
(000 1) plane is taken s a principal light emission facet. Here,
the one facet composed of the substantial (0001) plane is easy to
oxidize because it is easily covered with a Group 13 element. On
the other hand, the other facet composed of the substantial (000 1)
plane is difficult to oxidize because it is easily covered with N
atoms. This inhibits the principal light emission facet from being
degraded by oxidation, making a stable high power operation
feasible.
[0184] (b) Effect of Protective Film Covering Light Emission Facet
1Fa and Rear Facet 1Ba
[0185] In the fifth embodiment, the light emission facet 1Fa
composed of the (000 1) plane is easily covered with N atoms
because it is an N polar plane. The AlN film 231 serving as a
nitride film is formed on the light emission facet 1Fa. Since the
AlN film 231 thus includes N atoms covering the light emission
facet 1Fa, adhesion between the light emission facet 1Fa and the
AlN film 231 is enhanced. This sufficiently prevents the AlN film
231 from being stripped from the light emission facet 1Fa.
[0186] On the other hand, the rear facet 1Ba composed of the (0001)
plane is easily covered with Ga atoms because it is a Ga polar
plane. The Al.sub.2O.sub.3 film 291 serving as an oxide film is
formed on the rear facet 1Ba. This causes binding of a Ga atom and
an O atom to be formed in the interface between the rear facet 1Ba
and the Al.sub.2O.sub.3 film 291.
[0187] Binding energy between a Ga atom and an O atom is
significantly higher than binding energy between an O atom and an N
atom. In a case where the Al.sub.2O.sub.3 film 241 serving as an
oxide film is formed on the rear facet 1Ba, therefore, stripping of
the Al.sub.2O.sub.3 film 241 from the rear facet 1Ba is more
sufficiently prevented, as compared with that in a case where the
nitride film is formed on the rear facet 1Ba. Therefore, the
reliability of the nitride based semiconductor laser device 1 is
improved.
[0188] In the sixth embodiment, the AlO.sub.XN.sub.Y film (X<Y)
231a serving as a nitride film in which the nitrogen composition
ratio is higher than the oxygen composition ratio is formed on the
light emission facet 1Fa composed of the (000 1) plane. This
sufficiently prevents the AlO.sub.XN.sub.Y film (X<Y) 231a from
being stripped from the light emission facet 1Fa. Furthermore, the
AlO.sub.XN.sub.Y film (X>Y) 241a serving as an oxide film in
which the oxygen composition ratio is higher than the nitrogen
composition ratio is formed on the rear facet 1Ba composed of the
(0001) plane. This sufficiently prevents the AlO.sub.XN.sub.Y film
(X>Y) 241a from being stripped from the rear facet 1Ba.
[0189] In the seventh embodiment, the AlN film 231b serving as a
nitride film is formed on the light emission facet 1Fa composed of
the (000 1) plane. This sufficiently prevents the AlN film 231b
from being stripped from the light emission facet 1Fa. Furthermore,
the Al.sub.2O.sub.3 film 291b serving as an oxide film is formed on
the rear facet 1Ba composed of the (0001) plane. This sufficiently
prevents the Al.sub.2O.sub.3 film 241b from being stripped from the
rear facet 1Ba.
[0190] In the eighth embodiment, the AlO.sub.XN.sub.Y film (X<Y)
231c serving as a nitride film in which the nitrogen composition
ratio is higher than the oxygen composition ratio is formed on the
light emission facet 1Fa composed of the (000 1) plane. This
sufficiently prevents the AlO.sub.XN.sub.Y film (X<Y) 231c from
being stripped from the light emission facet 1Fa. Furthermore, the
AlO.sub.XN.sub.Y film (X>Y) 241c serving as an oxide film in
which the oxygen composition ratio is higher than the nitrogen
composition ratio is formed on the rear facet 1Ba composed of the
(0001) plane. This sufficiently prevents the AlO.sub.XN.sub.Y film
(X>Y) 241c from being stripped from the rear facet 1Ba.
[0191] (c) Effect of Taking (000 1) Plane as Light Emission Facet
1F
[0192] The (0001) plane serving as a Ga polar plane is easy to
oxidize because its top surface is easily covered with Ga atoms. On
the other hand, the (000 1) plane serving as a N polar plane is
difficult to oxidize because its top surface is easily covered with
N atoms.
[0193] In the present embodiment, the (000 1) plane is taken as the
light emission facet 1Fa. This inhibits the light emission facet
1Fa from being degraded by oxidation. This allows the laser
characteristics of the nitride based semiconductor laser device 1
to be kept stable, making a stable high power operation
feasible.
[0194] Furthermore, in the present embodiment, undoped
In.sub.0.15Ga.sub.0.85N is used as the well layer 106b. When the In
composition ratio is significantly lower than the Ga composition
ratio in the well layer 106b, the recesses and projections of the
active layer 106 in each of the light emission facet 1Fa and the
rear facet 1Ba are sufficiently inhibited from becoming
significant.
[0195] In the (000 1) plane where greater recesses and projections
are more easily formed than those in the (0001) plane, the recesses
and projections are prevented from becoming significant. As a
result, when the scattering of the laser light emitted from the
light emission facet 1Fa is reduced, so that a preferable far field
pattern having few ripples is obtained.
13. Modified Example of Fifth to Eighth Embodiments
[0196] A modified example of the fifth to eighth embodiments will
be then described. The following is the difference between the
nitride based semiconductor laser device 1 according to the
above-mentioned embodiments and the nitride based semiconductor
laser device 1 in this example.
[0197] Al.sub.0.03Ga.sub.0.97N is used as the n-type cladding layer
103 and the p-type cladding layer 109 in this example. The amount
of doping of Si into the n-type cladding layer 103 and the amount
of doping of Mg into the p-type cladding layer 109 are the same as
those in the second embodiment. Furthermore, the respective carrier
concentrations and thicknesses of the n-type cladding layer 103 and
the p-type cladding layer 109 are the same as those in the
above-mentioned embodiments.
[0198] An n-type GaN is used as the n-type optical guide layer 105,
n-type Al.sub.0.10Ga.sub.0.90N is used as the n-type carrier
blocking layer 104, and n-type In.sub.0.05Ga.sub.0.95N is used as
the n-type optical guide layer 105. The respective amounts of
doping of Mg into the n-type carrier blocking layer 104 and the
n-type optical guide layer 105 are the same as those in the second
embodiment. Furthermore, the respective carrier concentrations and
thicknesses of the n-type carrier blocking layer 104 and the n-type
optical guide layer 105 are the same as those in the
above-mentioned embodiments.
[0199] An active layer 106 having an MQW structure in which three
barrier layers 106a composed of undoped In.sub.0.25Ga.sub.0.75N and
two well layers 106b composed of undoped In.sub.0.55Ga.sub.0.45N
are alternately laminated is used in this example. The respective
thicknesses of each of the barrier layers 106a and each of the well
layers 106b are the same as those in the above-mentioned
embodiments.
[0200] P-type In.sub.0.05Ga.sub.0.95N is used as a p-type optical
guide layer 107, and p-type AlO.sub.0.10Ga.sub.0.90N is used as a
p-type cap layer 108 in this example. The respective amounts of
doping of Mg into the p-type optical guide layer 107 and the p-type
cap layer 108 are the same as those in the above-mentioned
embodiments. Furthermore, the respective carrier concentrations and
thicknesses of the p-type optical guide layer 107 and the p-type
cap layer 108 are the same as those in the above-mentioned
embodiments.
[0201] In this example, the In composition ratio included in the
active layer 106 is higher than the Ga composition ratio included
therein. In this case, a portion of the active layer 106 in the
light emission facet 1Fa is easier to oxidize. Therefore, taking
the (000 1) plane that is difficult to oxidize as the light
emission facet 1Fa can inhibit the light emission facet 1Fa from
being degraded by oxidation. This allows the laser characteristics
of the nitride based semiconductor laser device 1 to be kept
stable, making a stable high power operation feasible.
14. Other Embodiments
[0202] (1) Although in the above-mentioned embodiments, the oxide
films in the first to fourth dielectric multilayer films 210, 220,
230, 240 are formed of Al.sub.2O.sub.3, the nitride film is formed
of AlN, and the oxynitride film is formed of AlO.sub.XN.sub.Y, the
present invention is not limited to the same. The oxide films in
the first to fourth dielectric multilayer films 210, 220, 230, and
240 may be formed of one or more of Al.sub.2O.sub.3, SiO.sub.2,
ZrO.sub.2, Ta.sub.2O.sub.5, HfO.sub.2, and AlSiO.sub.X, for
example. Here, X is a real number larger than zero. The nitride
films in the first to fourth dielectric multilayer films 210, 220,
230, and 240 may be formed of one or both of AlN and
Si.sub.3N.sub.4, for example. Furthermore, the oxynitride film may
be formed of one or more of AlO.sub.XN.sub.Y, SiO.sub.XN.sub.Y and
TaO.sub.XN.sub.Y, for example. Here, X and Y are real numbers
larger than zero.
[0203] In the above-mentioned embodiments, the ratio of the
nitrogen composition ratio to the oxygen composition ratio in each
of the AlO.sub.XN.sub.Y film (X<Y) 221a, 212b, 222b, 212c, 221c,
231a, 232b, 242b, 231c, and 242c is 54(%):46(%), for example.
[0204] Although in the above-mentioned embodiments, SiO.sub.2 is
used as a material for a low refractive index film, and TiO.sub.2
is used as a material for a high refractive index film, the present
invention is not limited to the same. Another material such as
MgF.sub.2 or Al.sub.2O.sub.3 may be used as a material for a low
refractive index film. Another material such as ZrO.sub.2,
Ta.sub.2O.sub.5, CeO.sub.2, Y.sub.2O.sub.3, Nb.sub.2O.sub.5, or
HfO.sub.2 may be used as a material for a high refractive index
film.
[0205] (2) When at least one of the light emission facet 1F and the
rear facet 1B or at least one of the light emission facet 1Fa and
the rear facet 1Ba is formed by cleavage, a main surface of the
active layer 106 may have any plane direction in a range of
.+-.approximately 0.3 degrees from a (H, K, --H--K, 0) plane. Note
that H and K are any integers, and at least one of H and K is an
integer other than zero. Furthermore, the light emission facets 1F
and 1Fa and the rear facets 1B and 1Ba that are formed by cleavage
may respectively have any plane directions in a range of
.+-.approximately 0.3 degrees from the (0001) plane and the (000 1)
plane.
[0206] When the light emission facets 1F and 1Fa and the rear
facets 1B and 1Ba are formed by methods other than cleavage, for
example, etching, grinding, or selective growth, the light emission
facets 1F and 1Fa and the rear facets 1B and 1Ba may respectively
have any plane directions in a range of .+-.approximately 25
degrees from the (0001) plane and the (000 1) plane. However, it is
desired that the light emission facets 1F and 1Fa and the rear
facets 1B and 1Ba are substantially perpendicular (90
degrees.+-.approximately 5 degrees) to the main surface of the
active layer 106.
[0207] (3) A nitride of a Group 13 element including at least one
of Ga, Al, In, Tl, and B can be used for the substrate 101, the
n-type layer 102, the n-type cladding layer 103, the n-type carrier
blocking layer 104, the n-type optical guide layer 105, the active
layer 106, the p-type optical guide layer 107, the p-type cap layer
108, the p-type cladding layer 109, and the p-type contact layer
110. Specifically, a nitride based semiconductor composed of AlN,
InN, BN, TlN, GaN, AlGaN, InGaN, InAlGa or their mixed crystals can
be used as a material for each of the layers.
[0208] (4) In the first, third, fifth and seventh embodiments, when
an AlN film is formed on the other facet (000 1), as the protection
film of the first layer being in contact with the semiconductor,
the AlN film may be formed to have high orientation in the (000 1)
direction. In this case, thermal conductivity in the (000 1)
direction becomes increased, and a temperature rise at the
semiconductor interface can be suppressed, resulting in improved
reliability.
[0209] When a second AlN film is further formed as a layer other
than the protection film of the first layer as the first and fifth
embodiments, the orientation of the AlN film of the first layer
need not necessarily coincide with that of the second AlN film, and
the second AlN film need not necessarily be formed to have high
orientation as with the AlN film of the first layer.
[0210] While preferred embodiments of the present invention have
been described above, it is to be understood that variations and
modifications will be apparent to those skilled in the art without
departing the scope and spirit of the present invention. The scope
of the present invention, therefore, is to be determined solely by
the following claims.
* * * * *