Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2000-08-07
2002-06-04
Leung, Quyen (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S045013
Reexamination Certificate
active
06400743
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser device having a current confinement structure and an index-guided structure, and a process for producing a u semiconductor light emitting device having a current confinement structure and an index-guided structure.
2. Description of the Related Art
(1) In many conventional current semiconductor laser devices which emit light in the 0.9 to 1.1 &mgr;m band, a current confinement structure and index-guided structure are provided in crystal layers which constitute the semiconductor laser devices so that the semiconductor laser device oscillates in a fundamental transverse mode. For example, IEEE Journal of Selected Topics in Quantum Electronics, vol. 1, No. 2, 1995, pp.102 discloses a semiconductor laser device which emits light in the 0.98 &mgr;m band. This semiconductor laser device is formed as follows.
On an n-type GaAs substrate, an n-type Al
0.48
Ga
0.52
As lower cladding layer, an undoped Al
0.2
Ga
0.8
As optical waveguide layer, an Al
0.2
Ga
0.8
As/In
0.2
Ga
0.8
As double quantum well active layer, an undoped Al
0.2
Ga
0.8
As optical waveguide layer, a p-type AlGaAs first upper cladding layer, a p-type Al
0.67
Ga
0.33
As etching stop layer, a p-type Al
0.48
Ga
0.52
As second upper cladding layer, a p-type GaAs cap layer, and an insulation film are formed in this order. Next, a narrow-stripe ridge structure is formed above the p-type Al
0.67
Ga
0.33
As etching stop layer by normal photolithography and selective etching, and an n-type Al
0.7
Ga
0.3
As and n-type GaAs materials are embedded in both sides of the ridge structure by selective MOCVD using Cl gas. Then, the insulation film is removed, and thereafter a p-type GaAs layer is formed. Thus, a current confinement structure and an index-guided structure are built in the semiconductor laser device.
However, the above semiconductor laser device has a drawback that it is very difficult to form the AlGaAs second upper cladding layer on the AlGaAs first upper cladding layer, since the AlGaAs first upper cladding layer contains a high Al content and is prone to oxidation, and selective growth of the AlGaAs second upper cladding layer is difficult.
(2) In addition, IEEE Journal of Quantum Electronics, vol. 29, No. 6, 1993, pp.1936 discloses a semiconductor laser device which oscillates in a fundamental transverse mode, and emits light in the 0.98 to 1.02 &mgr;m band. This semiconductor laser device is formed as follows.
On an n-type GaAs substrate, an n-type Al
0.4
Ga
0.6
As lower cladding layer, an undoped Al
0.2
Ga
0.8
As optical waveguide layer, a GaAs/InGaAs double quantum well active layer, an undoped Al
0.2
Ga
0.8
As optical waveguide layer, a p-type Al
0.4
Ga
0.6
As upper cladding layer, a p-type GaAs cap layer, and an insulation film are formed in this order. Next, a narrow-stripe ridge structure is formed above a mid-thickness of the p-type Al
0.4
Ga
0.6
As upper cladding layer by normal photolithography and selective etching, and an n-type In
0.5
Ga
0.5
P material and an n-type GaAs material are embedded in both sides of the ridge structure by selective MOCVD. Finally, the insulation film is removed, and then electrodes are formed. Thus, a current confinement structure and an index-guided structure are realized in the layered construction.
However, the above semiconductor laser device also has a drawback that it is very difficult to form the InGaP layer on the AlGaAs upper cladding layer, since the AlGaAs upper cladding layer contains a high Al content and is prone to oxidation, and it is difficult to grow an InGaP layer having different V-group component, on such an upper cladding layer.
(3) Further, IEEE Journal of Selected Topics in Quantum Electronics, vol. 1, No. 2, 1995, pp.189 discloses an all-layer-Aluminum-free semiconductor laser device which oscillates in a fundamental transverse mode, and emits light in the 0.98 &mgr;m band. This semiconductor laser device is formed as follows.
On an n-type GaAs substrate, an n-type InGaP cladding layer, an undoped InGaAsP optical waveguide layer, an InGaAsP tensile strain barrier layer, an InGaAs double quantum well active layer, an InGaAsP tensile strain barrier layer, an undoped InGaAsP optical waveguide layer, a p-type InGaP first upper cladding layer, a p-type GaAs optical waveguide layer, a p-type ten InGaP second upper cladding layer, a p-type GaAs cap layer, and an insulation film are formed in this order. Next, a narrow-stripe ridge structure is formed above or the p-type InGaP first upper cladding layer by normal photolithography and selective etching, and an n-type In
0.5
Ga
0.5
P material is embedded in both sides of the ridge structure by selective MOCVD. Finally, the insulation film is removed, and a p-type GaAs contact layer is formed. Thus, a current confinement structure and an index-guided structure are realized.
The reliability of the above semiconductor laser device is improved since the strain in the active layer can be compensated for. However, the above semiconductor laser device also has a drawback that the kink level is low (about 150 mW) due to poor controllability of the ridge width.
(4) Furthermore, IEEE Journal of Quantum Electronics, vol. 29, No. 6, 1993, pp.1889 discloses an internal striped structure semiconductor laser device which oscillates in a fundamental transverse mode, and emits light in the 0.8 &mgr;m band. This semiconductor laser device is formed as follows.
On an n-type GaAs substrate, an n-type AlGaAs lower cladding layer, an AlGaAs/GaAs triple quantum well active layer, a p-type AlGaAs first upper cladding layer, an n-type AlGaAs current confinement layer, and an n-type AlGaAs protection layer are formed in this order. Next, a narrow-stripe groove is formed, by normal photolithography and selective etching, to such a depth that the groove penetrates the n-type AlGaAs current confinement layer. Next, over the above structure, a p-type AlGaAs second upper cladding layer and a p-type GaAs contact layer are formed.
In the above semiconductor laser device, the stripe width can be controlled accurately, and high-output-power oscillation in a fundamental transverse mode can be realized by the difference in the refractive index between the n-type AlGaAs current confinement layer and the p-type AlGaAs second upper cladding layer. However, the above semiconductor laser device also has a drawback that it is difficult to form an AlGaAs layer on another AlGaAs layer since the AlGaAs layers are prone to oxidation.
As described above, the conventional current semiconductor laser devices which include a current confinement structure and an index-guided structure, oscillate in a fundamental transverse mode, and emit light in the 0.9 to 1.1 &mgr;m band with high output power, are unreliable, or uneasy to produce, or have poor characteristics.
(5) Alternatively, in many conventional current semiconductor laser devices which emit light in the 0.9 to 1.1 &mgr;m band, a current confinement structure is provided in crystal layers which constitute the semiconductor laser devices so as to oscillate in a fundamental transverse mode. For example, Proceedings of SPIE, vol. 3628, 1999, pp.38-45 discloses an internal striped structure semiconductor laser device which emits light in the 0.98 &mgr;m band. This semiconductor laser device is formed as follows.
On an n-type GaAs substrate, an n-type Al
x
Ga
1-x
As lower cladding layer, an n-type GaAs optical waveguide layer, an InGaAs quantum well active layer, a p-type GaAs first upper optical waveguide layer, and an n-type Al
y
Ga
1-y
As current confinement layer are formed in this order. Next, a narrow-stripe groove is formed, by normal photolithography and selective etching, to such a depth that the groove penetrates the n-type AlGaAs current confinement layer. Next, over the above structure, a GaAs second optical waveguide layer, a p-type AlGaAs upper cladding layer, and a p-type GaAs contact layer are formed.
In the above semiconductor laser device, the stripe width can be controlled accurately, an
Fukunaga Toshiaki
Wada Mitsugu
Fuji Photo Film Co. , Ltd.
Leung Quyen
Sughrue & Mion, PLLC
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