Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2000-03-02
2002-09-10
Leung, Quyen (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S045013
Reexamination Certificate
active
06449300
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates a surface-emitting laser having a first distributed Bragg reflector composed of two kinds of thin film stacked alternately, an active layer and a second distributed Bragg reflector composed of two kinds of thin film stacked alternately which are formed on a semiconductor substrate successively.
2. Description of the Prior Art
Recently, a diode or a transistor widely used as a semiconductor element has a metal-oxide-semiconductor structure composed of a semiconductor layer, an insulating film obtained by oxidizing an arsenic aluminum (AlAs) layer formed on the semiconductor layer and a metallic film formed on the insulating film. The technique is suggested by universities in the United Stated, etc that by applying the manufacturing method of metaloxide-semiconductor structure for a surface-emitting laser, the AlAs layer or the gallium arsenic aluminum (GaAlAs) layer constituting the structure is selectively oxidized from its sides and thereby, a current path is restricted and the current is flown in a local area. It is known that the surface-emitting laser produced by applying the technique has enhanced characteristics in operation current, operation efficiency, etc.
FIGS. 1 and 2
are principle structures of conventional examples in a surface-emitting laser having the above selective oxidation structure, respectively.
A surface-emitting laser shown in
FIG. 1
has a semiconductor substrate
51
, a first distributed Bragg reflector
54
, an active layer
55
and a second distributed Bragg reflector
56
. The first and the second reflectors are composed of alternately stacked GaAs layers
52
and GaAlAs layers
53
, respectively. Moreover, between at least one of the reflectors
54
,
56
(the reflector
56
in the figure) and the active layer
55
is provided a current stenosed layer
57
formed by oxidizing a given area in a remote junction surface of an AlAs layer
58
, which is formed between the reflector
56
and the active layer
55
. In this example, the current stenosed layer
57
restricts a current path.
A surface-emitting laser shown in
FIG. 2
has a semiconductor substrate
51
, a first distributed Bragg reflector
54
, an active layer
55
and a second distributed Bragg reflector
56
. The first and the second reflectors are composed of alternately stacked GaAs layers
52
and AlAs layers
53
, respectively. Moreover, the whole stacked structure, including the reflectors
54
,
56
, is oxidized. In this example, the nearest one of the plural oxidized AlAs layers to the active layer
55
serves as a current-stenosed layer and restricts a current path. The plural oxidized AlAs layers near the active layer reduce the capacitance of the surface-emitting laser itself to some degree.
The conventional surface-emitting laser shown in
FIG. 1
can restrict the current path by the current stenosed layer
57
formed on the active layer
55
, but the above structure increases the capacitance of the surface-emitting laser itself including the structure. Thus, in trying to operate the laser at a high speed, the laser has difficulty in response to external signals, so that its high speed operation can not be realized.
Moreover, it is conceivable that by forming a current blocking layer through implantation protons in the above structure, the capacitance of the surface-emitting laser is reduced. In this case, however, a processing equipment exclusively for the proton-implantation is needed, resulting in the increase in cost. Furthermore, semiconductor layers constituting the distributed Bragg reflector suffer from the proton-implantation, resulting in the occurrence of defect in the layers and it is difficult to control a implantation position in a thickness direction of the above structure. Accordingly, this implantation method has difficulty in being actually adopted.
On the other hand, the surface-emitting laser shown in
FIG. 2
can restrict a current path by the plural oxidized AlAs layers and reduce the capacitance of the laser to some degree. However, a light generated in the surface-emitting laser is scattered at the boundary between the oxidized area and the non-oxidized area in the adjacent AlAs layer to the one serving as the current stenosed layer. Accordingly, the emitting efficiency of the light emitted to outside from the surface-emitting laser is degraded, resulting in the deterioration of the laser's performance and it is very difficult to emit the light having a “single mode peak”.
SUMMERY OF THE INVENTION
It is an object of the present invention to iron out the above problems by providing, in a surface-emitting laser, a capacitance reducing layer able to reduce the capacitance of the laser without scattering of a light emitted to outside.
The first invention claimed in claim 1 relates to a surface-emitting laser in which a first distributed Bragg reflector composed of an alternately stacked structure made of two kinds of thin film, an active layer and a second distributed Bragg reflector composed of an alternately stacked structure made of two kinds of thin film, are formed on a semiconductor substrate, successively, comprising a current stenosed layer having an oxidized area in a remote junction surface therein between at least one of the first and the second distributed Bragg reflectors and the active layer, and plural capacitance-reducing layers, each layer having a smaller oxidized area than the oxidized area in a remote junction surface constituting the current stenosed layer, at least one of the first and the second distributed Bragg reflectors, the plural capacitance-reducing layers, the current stenosed layer and the active layer being arranged successively, one of the first and the second distributed Bragg reflectors constituting a first conductive type Bragg reflector, the other constituting a second conductive type Bragg reflector.
The second invention claimed in claim 2 relates to the surface-emitting laser in which the first and the second distributed Bragg reflectors are composed of alternately stacked Ga
x
Al
1−x
As (herein, 0≦x≦1) layers and Ga
y
Al
1−y
As (herein, 0≦y≦1).
The third invention claimed in claim 3 relates to the surface-emitting laser in which the current stenosed layer is composed of the plural semiconductor layers, the semiconductor layer at its junction surface being composed of an AlAs layer having a thickness of 10-30 nm and the capacitance-reducing layer is composed of a GaAlAs layer having a thickness of about 80 nm, and total thickness between the first and the second distributed Bragg reflectors is one-fourth of the emitting wavelength from the surface-emitting laser.
The fourth invention claimed in claim 4 relates to the surface-emitting laser in which the current stenosed layer is composed of an AlAs layer and the capacitance-reducing layer is composed of an AlAs layer having a thinner thickness than that of the current stenosed layer.
In the first invention, when an anode electrode and a cathode electrode are provided on the second distributed Bragg reflector and the semiconductor substrate, respectively, an injected current flows only through the non-oxidized area of the current stenosed layer and reaches the local part of the active layer because the oxidized area formed except the center of the remote junction surface from the active layer in the semiconductor constituting the stenosed layer is insulative and does not flow the current through itself. As a result, the part of the active layer corresponding to the non-oxidized area is selectively excited and generates a light, which is amplified by the reflection between the first and the second distributed Bragg reflectors and is emitted. The generated light is scattered at the boundary between the oxidized area and the non-oxidized area in the semiconductor layer constituting the current stenosed layer. However, since the capacitance-reducing layer, adjacent to the current stenosed layer, has a larger non-oxidized area than that of the stenosed layer, the genera
Iga Kenichi
Koyama Fumio
Nishiyama Nobuhiko
Leung Quyen
Schneller Marina V.
Tokyo Institute of Technology
Venable
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