Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2002-03-27
2003-12-23
Ip, Paul (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S043010
Reexamination Certificate
active
06668002
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser device including an ARROW (Antiresonant Reflecting Optical Waveguide) structure. The present invention also relates to a process for producing a semiconductor laser device including an ARROW structure.
2. Description of the Related Art
A reliable high-power semiconductor laser device which emits a high-quality, diffraction-limited beam is required for use as a light source for exciting an optical fiber amplifier.
U.S. Pat. No. 5,606,570 discloses a semiconductor laser device having an ARROW (Antiresonant Reflecting Optical Waveguide) structure as a semiconductor laser device which can emit a high-power, diffraction-limited laser beam in the 980 nm band. The ARROW structure is a structure for confining light in a core region. The disclosed ARROW structure includes a plurality of core regions having a low equivalent (effective) refractive index, high-refractive-index regions which have a high equivalent refractive index and are arranged between the plurality of core regions and on the outer sides of the plurality of core regions, and low-refractive-index regions which have a low equivalent refractive index and are arranged on the outer sides of the outermost ones of the high-refractive-index regions. The high-refractive-index regions function as a reflector of light in the fundamental mode, and the low-refractive-index regions suppress leakage of light. Thus, the semiconductor laser device can be controlled so as to operate in the fundamental transverse mode.
In addition, it is reported that a preferable value of the width d
b1
′ of each of the outermost ones of the high-refractive-index regions is determined in accordance with the equation (1), a preferable value of the width d
b2
′ of each of the high-refractive-index regions arranged between the plurality of core regions is determined in accordance with the equation (2), and a preferable value of the width of each of the low-refractive-index regions is d
c
′/2, where d
c
′ is the width of each of the plurality of core regions. In the equations (1) and (2), &lgr; is the oscillation wavelength, n
c
′ is the equivalent refractive index of the plurality of core regions, and n
b
′ is the equivalent refractive index of the high-refractive-index regions.
d
b1
′
=
3
λ
4
{
n
b
′2
-
n
c
′2
+
(
λ
2
d
c
′
)
2
}
1
2
(
1
)
d
b2
′
=
λ
2
{
n
b
′2
-
n
c
′2
+
(
λ
2
d
c
′
)
2
}
1
2
(
2
)
However, the semiconductor laser device disclosed in U.S. Pat. No. 5,606,570 includes an active layer made of InGaAs, and the ARROW structure is formed with a current confinement layer made of InGaAlP and a high-refractive-index region made of GaAs by using a regrowth technique. In addition, GaAs and InGaP layers (or InAlP, GaAs, and InGaP layers) are exposed at the base surface on which a cladding layer is regrown. Therefore, P—As interdiffusion occurs at the exposed surface during a process of raising temperature for the regrowth, and thus the regrowth is likely to become defective. As a result, the above semiconductor laser device is not actually used. Further, there is a high degree of technical difficultly in regrowing layers when a layer (such as the InAlP layer) exposed at the base surface on which the cladding layer is regrown contains aluminum, which is prone to oxidation.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a semiconductor laser device which includes an ARROW structure and is not technically difficult to produce.
Another object of the present invention is to provide a process for producing with high precision a reliable semiconductor laser device which includes an ARROW structure.
(I) According to the first aspect of the present invention, there is provided a semiconductor laser device comprising: a GaAs substrate of a first conductive type; a first lower cladding layer formed above the GaAs substrate and made of In
0.49
Ga
0.51
P of the first conductive type; a lower optical waveguide layer formed above the first lower cladding layer and made of In
x1
Ga
1-x1
As
1-y1
P
y1
which is undoped or the first conductive type, where x1=0.49y1 and 0≦y1≦0.3; a compressive-strain quantum-well active layer formed above the lower optical waveguide layer and made of In
x3
Ga
1-x3
As
1-y3
P
y3
where 0.49y3<x3 ≦0.4 and 0≦y3≦0.1; an upper optical waveguide layer formed above the compressive-strain quantum-well active layer and made of In
x1
Ga
1-x1
As
1-y3
P
y1
which is undoped or a second conductive type, where x1=0.49y1 and 0≦y1≦0.3; a first upper cladding layer of the second conductive type, formed above the upper optical waveguide layer and made of one of In
0.49
Ga
0.51
P and Al
x
Ga
1-x
As which has an approximately identical refractive index to a refractive index of In
0.49
Ga
0.51
P, where 0.45≦x≦0.55; a first etching stop layer formed above the first upper cladding layer and made of GaAs of the second conductive type; a second etching stop layer made of In
x8
Ga
1-x8
P of the second conductive type and formed above the first etching stop layer other than stripe areas of the first etching stop layer corresponding to at least one current injection region and low-refractive-index regions located on outer sides of the at least one current injection region and separated from the at least one current injection region or outermost ones of the at least one current injection region by a predetermined interval, where 0≦x8≦1, and the stripe areas of the first etching stop layer extend in a direction of a laser resonator; a first current confinement layer made of GaAs of the first conductive type and formed above the second etching stop layer; a third etching stop layer made of In
x9
Ga
1-x9
P of the second conductive type and formed over the first current confinement layer and the stripe areas of the first etching stop layer, where 0≦x9≦1; a fourth etching stop layer made of GaAs of the second conductive type and formed above the third etching stop layer other than at least one stripe area of the third etching stop layer corresponding to the at least one current injection region; a second current confinement layer made of In
0.49
Ga
0.51
P of the first conductive type and formed above the fourth etching stop layer; a second upper cladding layer of the second conductive type, formed above the second current confinement layer and the at least one stripe area of the third etching stop layer, and made of one of In
0.49
Ga
0.51
P and Al
x
Ga
1-x
As which has an approximately identical refractive index to the refractive index of In
0.49
Ga
0.51
P, where 0.45≦x≦0.55; and a contact layer made of GaAs of the second conductive type and formed above the second upper cladding layer.
(i) The current injection region may have a width equal to or greater than 3 micrometers.
(ii) The first current confinement layer may include first and second sublayers made of GaAs of the first conductive type, and a quantum-well layer formed between the first and second sublayers and made of an InGaAs material which has a smaller bandgap than the bandgap of the compressive-strain quantum-well active layer.
(iii) The semiconductor laser device according to the first aspect of the present invention may further comprise a second lower cladding layer made of Al
x
Ga
1-x
As of the first conductive type and formed between the GaAs substrate and the first lower cladding layer, where 0.45≦x≦0.55. In this case, it is preferable that the thickness of the InGaP lower cladding layer does not exceed 0.5 micrometers.
(II) According to the second aspect of the present invention, there is provided a process for producing a semiconductor laser device, comprising the steps of: (a) forming above a GaAs substrate of a first conductive type a lower cladding layer made of In
0.49
Ga
0.51
P of the first conductive type; (b) forming above the lower c
Ip Paul
Nguyen Dung
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