Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Compound semiconductor
Reexamination Certificate
1999-09-24
2002-05-14
Christianson, Keith (Department: 2813)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Compound semiconductor
Reexamination Certificate
active
06387721
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a semiconductor light-emitting device and a manufacturing method for the same. More particularly, this invention relates to a semiconductor light-emitting device of a ridge type having a current blocking layer at a specific portion and a manufacturing method for the same. The invented semiconductor light-emitting device is suitable for a semiconductor laser. In use of a structure of the semiconductor light-emitting device according to the invention, currents can be adequately squeezed, and production yield can be improved during cleaverage and assembly. Besides a semiconductor light-emitting device having a high output and a longer life span can be provided when the device with this structure is assembled in a junction-down type.
2. Description of Related Art
FIG. 4
shows a structure of and a manufacturing method for a conventional ridge waveguide type stripe structure semiconductor laser device.
As shown in FIG.
4
(
a
), first, a first conductive type cladding layer
11
, an active layer
12
, a second conductive taupe cladding layer
13
, and a second conductive type contact layer
14
are grown on a substrate
21
. Secondly, the second conductive type contact layer
14
and the second conductive type cladding layer
13
are etched as shown in FIG.
4
(
b
) to form a ridge portion. During this step, portions other than the ridge portion are etched to remain a prescribed thickness of the second conductive type cladding layer
13
located or the active layer
12
. Protective film
31
made of an insulator is formed on the ridge portion side surfaces and surfaces other than the ridge portion to stop the current flowing. Lastly electrode
32
is formed on an epitaxial side including an area above the ridge portion and electrode
33
is formed on a substrate to produce the device (FIG.
4
(
c
)).
With such a structure, the currents are injected into the active layer
12
via the ridge portion, and the generated light corresponding to the composition of the active layer
12
is generated at the active layer
12
below the ridge portion. Since the protective film
31
having a smaller refractive index than semiconductor portions is formed, the effective refractive index of an active layer located below areas other than the ridge portion is smaller than the effective refractive index of the active layer below the ridge portion. Consequently, the generated light is confined in a light waveguide below the ridge portion.
Because in this ridge waveguide type stripe structure semiconductor light-emitting device, the ridge portion is formed by etching, it is difficult to control the thickness of the cladding layer portion of a non-ridge portion. Consequently, slight differences of the thickness of the cladding layer of the portions other than the ridge portion cause large fluctuations of the effective refractive index of the active layer of those portions. The width of the ridge bottom, which decides the width of current injection, is not controlled, and therefore, it is difficult to produce lasers having a low threshold and a constant off-angle with good reproducibility.
To solve such problems, a method has been proposed in which the thickness of the cladding layer over the active layer is decided by the crystal growth rate during a crystal growth, in which an isolation layer is formed on areas other than the ridge portion, and in which the ridge portion is re-grown at the ridge portion (e.g., Japanese Unexamined Patent Publication No. 5-121,822, Japanese Unexamined Patent Publication No. 9-199,791)
FIG. 5
shows a structure and a manufacturing method For such a laser device. First, after a first conductive type cladding layer
11
, an active layer
12
, and a second conductive type first cladding layer
13
are grown on the substrate
21
(FIG.
5
(
a
)). Secondly, the surface of the second conductive type first cladding layer
13
is covered with a protective film
31
such as SiO
2
or the like, and a second conductive type second cladding layer
13
a
and a second conductive type contact layer
14
a
are selectively grown only at a stripe region after a stripe shape window is opened by a photolithography method FIG.
5
(
b
)) Lastly, a protective film
31
a
such as SiN
x
is formed on side surfaces of the second conductive type second cladding layer
13
a
, the entire surface of the second conductive type contact layer
14
a
, and a protective film
31
covering areas other than the ridge portion. The SiN
x
protective film located on the top of the ridge portion is removed by a photolithography method. And electrode
32
is formed on the whole epitaxial surface and electrode
33
is formed on the substrate (FIG.
5
(
c
)).
Where such a protective film or the like makes the current squeezing, there raise problems that cleavage cannot be made easily due to the surface covered by the protective film as well as peeling off of the electrodes may occur. When the protective film has pinholes or the like, currents may flow through portions other than the rigde portion and there raises a problem that the current cannot be injected at the ridge portion. When the device is assembled in a junction-down type, in which the substrate side is upper while the epitaxial layer side is lower, a soldering material ray reach the compound semiconductor layers over the electrodes and the protective film, and there rises a problem that the current leakage may occur easily. Because the ridge portion is projecting from other regions, the device may be easily stressed and degraded. These are not in a favorable situation. The specification of U.S. Pat. No. 5,399, 855 discloses a semiconductor light-emitting device having a dummy ridge structure higher than the ridge structure on both sides of the ridge structure. But since the dummy ridge structure is covered by an insulation layer, the above problems regarding cleavage or peeling of electrodes remain unsolved.
With the conventional ridge type waveguide structure semiconductor light-emitting device, even where produced by re-growth, the LD (laser diode) in which currents are squeezed by means of the protective film or the like, cleavage and assembly are not easy, and the currents may not be squeezed adequately by the protective film or the like, so that the production yield may be lowered. When the device is assembled in the junction-down type, the device likely invite the current leakage to areas otter than the ridge portion or degradation due to stresses, so that the device hardly obtains adequate LD characteristics.
It is an object of the invention to provide a semiconductor light-emitting device wish a high production yield since readily cleaved and assembled, with adequately squeezed currents, and with, when assembled in the junction-down type, a high output and a longer life.
SUMMARY OF THE INVENTION
This the inventors have found that, as a result of diligent researches for accomplishing the above object, the above discussed problems are solved by a semiconductor light-emitting device having a structure formed with a semiconductor layer as a current blocking layer outside a protective film formed on both sides of a ridge portion, and completed this invention.
That is, first, this invention is to provide a semiconductor light-emitting device, where including a substrate, a first compound semiconductor layer including an active layer formed on the substrate, a second compound semiconductor layer or a ridge type formed on the first compound semiconductor layer, and a protective film formed above the first compound semiconductor layer on both sides of the second compound semiconductor layer, has a current blocking layer formed above the first compound semiconductor layer outside the protective film.
Secondly, this invention is to provide a method for manufacturing semiconductor light-emitting device comprising the steps of: forming a first compound semiconductor layer including an active layer on a substrate, and a protective film on a center portion of the first compound sem
Fujii Katsushi
Hashimoto Makiko
Hosoi Nobuyuki
Kiyomi Kazumasa
Sato Yoshihito
Armstrong Westerman & Hattori, LLP
Christianson Keith
Mitsubishi Chemical Corporation
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