Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Compound semiconductor
Reexamination Certificate
2003-04-02
2004-08-10
Lohe, Steven (Department: 2811)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Compound semiconductor
C438S022000, C438S047000, C438S956000, C257S094000, C257S096000, C257S097000, C257S103000, C372S045013, C372S046012, C372S049010
Reexamination Certificate
active
06773948
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser device having a nitride semiconductor crystal.
2. Description of the Related Art
A semiconductor laser device having a nitride semiconductor crystal is a laser device which oscillates within a wavelength band around a blue wavelength. It has been confirmed that such a laser device has a laser oscillation function.
Many semiconductor laser devices which have been confirmed to provide laser oscillation have a gain guiding structure or a simple ridge structure with no buried structure. For these semiconductor laser devices, there is a demand to improve the driving efficiency and to provide a waveguide which allows for a stable single transverse mode.
In the conventional ridge type semiconductor device, a GaN-type material is typically cleaved along the {1, −1, 0, 0} facet thereof to provide a cavity surface. This is because the {1, −1, 0, 0} facet of a GaN-type material provides a desirable cleaved surface.
A semiconductor laser device having a buried structure is known in the art as a type of semiconductor laser device which has both a desirable current constricting function and an optical waveguide characteristic with a low propagation loss.
A conventional semiconductor laser device having a buried structure will be described below with reference to FIG.
3
. Referring to
FIG. 3
, a buffer layer
2
of i-GaN and an n-side contact layer
3
of n-GaN are provided in this order on a substrate
1
. An n-side cladding layer
4
of n-Al
0.1
Ga
0.9
N is provided on a portion of the n-side contact layer
3
. A light emitting layer
5
having a multilayer structure, a first p-side cladding layer
6
of p-Al
0.1
Ga
0.9
N, and an n-type current blocking layer
7
of n-Al
0.2
Ga
0.8
N are provided in this order on-the n-side cladding layer
4
. The n-type current blocking layer
7
includes a stripe groove
7
a
which reaches the first p-side cladding layer
6
. The stripe groove
7
a
is provided to localize the electric current passing therethrough to a narrow area. A second p-side cladding layer
8
of p-Al
0.1
Ga
0.9
N is provided on the n-type current blocking layer
7
so as to fill up the groove
7
a
. A p-side contact layer
9
of p-GaN and a p-side electrode
10
are provided in this order on the second p-side cladding layer
8
.
An n-side electrode
11
is provided on the other portion of the n-side contact layer
3
.
If such a buried type semiconductor device has its cleaved surface along the {1, −1, 0, 0} facet, as in the ridge type semiconductor device, the stripe groove is formed along the <1, −1, 0, 0> direction of the n-type current blocking layer
7
.
FIG. 4
is a diagram illustrating a portion of an intermediate structure of the conventional semiconductor laser device during the crystal growth of the second p-side cladding layer
8
. As illustrated in
FIG. 4
, the second p-side cladding layer
8
being grown contains a large number of disturbed surfaces along the stripe groove
7
a.
In such a conventional semiconductor laser device, the crystal quality of the second p-side cladding layer
8
is quite poor along or near the stripe groove
7
a
. Such a semiconductor laser device has a substantial propagation loss. However, the poor crystal quality has not been addressed as a problem, or it has been neglected. The present inventors have found that each of the disturbed surfaces formed along the stripe groove
7
a
extends along the (1, −1, 0, 1) facet and at a certain angle with respect to the <1, −1, 0, 0> direction of the stripe groove.
SUMMARY OF THE INVENTION
According to one aspect of this invention, a semiconductor light emitting device includes: a substrate; a light emitting layer; a semiconductor layer of a hexagonal first III-group nitride crystal; and a cladding layer of a second III-group nitride crystal. A stripe groove is provided in the semiconductor layer along a <1, 1, −2, 0> direction.
Thus, the stripe groove is oriented along the <1, 1, −2, 0> direction, so that the crystal growth surface (1, −1, 0, 1) and the stripe groove are parallel to each other. As a result, a crystal grows along a surface which is substantially parallel to the side surface of the <1, 1, −2, 0> stripe groove. Thus, it is possible to prevent disturbed surfaces from being produced in the cladding layer, thereby improving the crystal quality in the vicinity of the groove.
In one embodiment of the invention, a slope of the stripe groove extends at an angle of about 20° to about 80° with respect to a primary surface of the substrate.
With such a structure, as the angle between the slope of the groove and the primary surface of the substrate is about 20° or more, it is possible to reduce the area of the semiconductor layer existing below the slope where the thickness of the semiconductor layer is small, and to suppress the current flowing through the semiconductor layer. Moreover, as the angle between the slope of the groove and the primary surface of the substrate is about 80° or less, it is possible to suppress the shift or variation in the composition of the III-group nitride material in the semiconductor layer or in the cladding layer.
In one embodiment of the invention, an electric resistivity of the semiconductor layer is larger than that of the cladding layer.
With such a structure, the resistance of the semiconductor layer can be increased, so that the semiconductor layer may function as a current blocking layer.
In one embodiment of the invention, a conductivity type of the semiconductor layer is opposite to that of the cladding layer.
With such a structure, as the conductivity type of the semiconductor layer is opposite to that of the cladding layer, the semiconductor layer may function as a current blocking layer.
In one embodiment of the invention, a refractive index of the semiconductor layer is smaller than that of the cladding layer.
With such a structure, it is possible to obtain a semiconductor light emitting device which realizes a single transverse mode current constricting function.
In one embodiment of the invention, the semiconductor layer includes Al
x
Ga
1−x
N (0≦x≦1), and the cladding layer includes Al
y
Ga
1−y
N (0≦y≦1 and y<x).
With such a structure, as the refractive index of the semiconductor layer is smaller than that of the cladding layer, it is possible to obtain a semiconductor light emitting device which realizes a single transverse mode current constricting function.
In one embodiment of the invention, the cladding layer includes a groove which extends along a (1, −1, 0, 1) facet.
With such a structure, it is possible to maintain a desirable crystal growth surface of the cladding layer, thereby improving the crystallinity of the cladding layer.
In one embodiment of the invention, the stripe groove is formed by an isotropic dry etching process.
With such a-structure, it is possible to obtain a semiconductor layer having a desirable crystal growth surface, thereby improving the crystallinity of the cladding layer.
According to another aspect of this invention, a method for producing a semiconductor light emitting device is provided. The method includes the steps of: providing a light emitting layer; providing a semiconductor layer of hexagonal first III-group nitride crystal; providing a stripe groove in the semiconductor layer along a <1, 1, −2, 0> direction by an isotropic dry etching process; and providing a cladding layer of a second III-group nitride crystal on the semiconductor layer after the step of providing the stripe groove.
With such a structure, as the stripe groove is provided in the semiconductor layer along the <1, 1, −2, 0> direction by an isotropic dry etching process, the slope of the groove in the semiconductor layer can be a desirable crystal growth surface.
In one embodiment of the invention, in the step of providing the stripe groove, a slope of the s
Imafuji Osamu
Ishida Masahiro
Nakamura Shinji
Orita Kenji
Yuri Masaaki
Kang Donghee
Lohe Steven
Matsushita Electric - Industrial Co., Ltd.
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