Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2000-11-15
2003-07-08
Paladini, Albert W. (Department: 2125)
Coherent light generators
Particular active media
Semiconductor
C372S044010, C257S079000
Reexamination Certificate
active
06590918
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for producing a semiconductor laser element, and specifically to a method for producing, with improved production yield, a high-output semiconductor laser element having an end face window structure. The present invention also relates to a semiconductor laser element which is produced by such a production method.
2. Description of the Related Art
In recent years, as a light source for an information processing apparatus which is used with an optical disk, such as a DVD (digital versatile disk), etc, a semiconductor laser element which is made by using AlGaInP mixed crystal and which emits light with a wavelength in the vicinity of 600 nm has been practically used. A rewritable optical disk such as a DVD requires an optical output of 30 mW or more. Moreover, in order to realize a smaller, faster information processing apparatus, an optical output of about 50 mW to 100 mW is required.
In general, deterioration in emission characteristics due to crystal breakage in a laser end face restricts the increase in output power of a semiconductor laser element. This is an important problem in a semiconductor laser element made using AlGaInP mixed crystal. In order to effectively increase the output power of a semiconductor laser element, the semiconductor laser element is provided with an end face window structure in which an end face of a laser cavity is made of a material transparent to laser light. An example of such an arrangement is disclosed in Suzuki, et al., “Electronics letters”, Vol. 20, p. 363, 1984. This document describes an end face window structure formed by utilizing a disorder phenomenon caused in a quantum well structure. Specifically, in a double hetero structure including a quantum well structure used as an active layer, impurities (atoms) are diffused in the quantum well structure, whereby a disorder phenomenon is caused in the quantum well structure.
FIG. 16
is a perspective view showing a conventional semiconductor laser element
900
. The semiconductor laser element
900
is a lateral mode controlled AlGaInP red semiconductor laser element which has an end face window structure produced by utilizing the disorder phenomenon as described above.
The semiconductor laser element
900
includes an n-type GaAs substrate
901
, an n-type AlGaInP cladding layer
902
, an active layer
903
which has a quantum well structure including a GaInP well layer (not shown) and an AlGaInP barrier layer (not shown), a p-type AlGaInP first cladding layer
904
, a p-type GaInP etching stop layer
905
, a p-type AlGaInP second cladding layer
906
, a p-type GaInP band discontinuity relaxation layer
907
, an n-type GaAs current confinement layer
908
, a p-type GaAs contact layer
909
, an n-electrode
911
, and a p-electrode
912
.
In the semiconductor laser element
900
having such a structure, the p-type AlGaInP second cladding layer
906
is formed so as to have a ridge shape, whereby lateral mode control of laser light is achieved. Furthermore, an impurity diffusion region
910
containing Zn atoms diffused therethrough is provided as an end face window structure of the laser element
900
.
Next, a method for producing the conventional semiconductor laser element
900
is described.
FIGS. 17A through 17F
show steps of producing the semiconductor laser element
900
. In FIG.
16
and
FIGS. 17A through 17F
, like reference numerals denote like parts. For the purpose of simplification, the production method is herein described for one semiconductor laser element
900
, although a plurality of semiconductor laser elements
900
are produced simultaneously in an actual production process.
In the first step, by an MOVPE (Metal Organic Vapor Phase Epitaxy) method, an n-type AlGaInP cladding layer
902
, an active layer
903
which has a quantum well structure including a GaInP well layer (not shown) and an AlGaInP barrier layer (not shown), a p-type AlGaInP first cladding layer
904
, a p-type GaInP etching stop layer
905
, a p-type AlGaInP second cladding layer
906
, and a p-type GaInP band discontinuity relaxation layer
907
are sequentially formed on an n-type GaAs substrate
901
, thereby obtaining a layered structure
900
a
having a double hetero structure as shown in FIG.
17
A.
Next, an SiO
2
film
913
is formed on the layered structure
900
a
, and the SiO
2
film
913
is patterned by wet etching so as to form stripe opening portions each having a width of several tens of micrometers at the interval of several hundreds of micrometers in a direction perpendicular to a cavity direction of a resulting laser element. Then, a ZnO film
914
is formed by sputtering entirely over the SiO
2
film
913
and in the stripe opening portions, and the ZnO film
914
is removed by wet-etching except for part of the ZnO film
914
which has been formed in the stripe opening portions, thereby obtaining a layered structure
900
b
as shown in FIG.
17
B.
Then, an SiO
2
film
915
is formed entirely over the upper surfaces of the SiO
2
film
913
and the ZnO film
914
. Thereafter, the resultant structure is annealed in a nitrogen atmosphere. In this annealing process, the ZnO film
914
formed in the stripe opening portions is used as a Zn provision layer to diffuse Zn atoms throughout the layers from the upper surface of the p-type GaInP band discontinuity relaxation layer
907
down to the n-type AlGaInP cladding layer
902
. As a result, the impurity diffusion region
910
is formed, whereby a layered structure
900
c
is obtained as shown in FIG.
17
C.
In the impurity diffusion region
910
, the active layer
903
having a quantum well structure which includes the GaInP well layer (not shown) and the AlGaInP barrier layer (not shown) is disordered. In the impurity diffusion region
910
, the band gap in a disordered portion of a quantum well is larger than that in a non-disordered portion, and thus, the disordered portion of the quantum well acts as an end face window structure.
Next, the SiO
2
film
913
, the ZnO film
914
, and the SiO
2
film
915
are removed by wet-etching, and an SiO
2
film
916
is formed over the upper surface of the resultant structure. The SiO
2
film
916
is patterned by wet-etching into a stripe shape so as to have a width of several micrometers. (As described above, in an actual production process, a plurality of semiconductor laser elements
900
are produced simultaneously, and a plurality of SiO
2
films
916
are formed into a stripe pattern so that the longitudinal direction of each stripe is equal to a laser cavity direction.) The SiO
2
films
916
are used as a mask to partially remove the p-type GaInP band discontinuity relaxation layer
907
by wet-etching so as to provide a ridge structure to the p-type GaInP band discontinuity relaxation layer
907
. Then, the p-type AlGaInP second cladding layer
906
is etched with a wet-etching solution which can selectively etch the p-type AlGaInP second cladding layer
906
, so that a ridge-shaped p-type AlGaInP second cladding layer
906
is formed. As a result, a layered structure
900
d
is obtained as shown in FIG.
17
D. (For example, sulfuric acid may be used as the wet-etching solution for the selective etching because the etching rate thereof is different for AlGaInP and for GaInP.) In the layered structure
900
d
, the p-type GaInP etching stop layer
905
is exposed in the region(s) from which the p-type AlGaInP second cladding layer
906
has been completely removed.
Then, the SiO
2
film
916
is also used as a mask for selective growth to grow, by an MOVPE method, an n-type GaAs current confinement layer
908
on the p-type GaInP etching stop layer
905
so as to cover side surfaces of the p-type AlGaInP second cladding layer
906
and the p-type GaInP band discontinuity relaxation layer
907
thereby obtaining a layered structure
900
e
as shown in FIG.
17
E.
Then, the SiO
2
film
916
is removed by wet-etching, and a p-type GaAs contact layer
909
is formed by an MOVPE method over th
Fukuhisa Toshiya
Mannou Masaya
Matsushita Electronics Corporation
Paladini Albert W.
RatnerPrestia
LandOfFree
Semiconductor laser device and method for producing the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Semiconductor laser device and method for producing the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor laser device and method for producing the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3076695