Active solid-state devices (e.g. – transistors – solid-state diode – Thin active physical layer which is
Reexamination Certificate
2002-03-22
2003-10-28
Meier, Stephen D. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Thin active physical layer which is
C257S021000, C257S024000
Reexamination Certificate
active
06639240
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a photosemiconductor device and a method for fabricating the photosemiconductor device, more specifically to a photosemiconductor device having quantum dots and a method for fabricating the photosemiconductor device.
Semiconductor light amplifiers and semiconductor lasers are small-sized and have small electric power consumptions, which makes them attractive in the fields of optical communication, etc.
A conventional semiconductor light amplifier will be explained with reference to FIG.
9
.
FIG. 9
is a sectional view of the conventional semiconductor light amplifier.
As shown in
FIG. 9
, a clad layer
112
of n type InP is formed on a semiconductor substrate
110
of n type InP. A bulk active layer
124
of InGaAs is formed on the clad layer
112
. A clad layer
136
is formed on the bulk active layer
124
. The clad layer
136
, the bulk active layer
124
and the clad layer
112
are formed in a mesa as a whole and form a mesa-shaped light waveguide layer
138
. A current constriction layer
118
is formed of a p type InP layer
118
a
and an n type InP layer
118
b
on both sides of the light waveguide layer
138
. A cap layer
140
is formed of n type InP on the light waveguide layer
138
and the current constriction layer
118
. AR (Anti-Reflection) coat film (not shown) is formed on both sides of the mesa-shaped light waveguide layer
138
. The conventional semiconductor light amplifier has such structure.
The use of a quantum well active layer in place of the bulk active layer
124
is also proposed. The use of the quantum well active layer can improve gains in comparison with the use of the bulk active layer.
However, the gain bandwidth of the conventional semiconductor light amplifier using the bulk active layer and the quantum well active layer is small. Accordingly, the conventional semiconductor light amplifier cannot amplify a WDM (Wavelength Division Multiplexing) signal of a wide band at once.
Here, injecting more current into the bulk active layer and the quantum well active layer increases numbers of electrons and holes stored in the bulk active layer and the quantum active layer, which will widen the gain bandwidth. However, the increase of the injected current to the bulk active layer and the quantum well active layer increases calorific powers, and temperatures of the bulk active layer and the quantum well active layer rise. Thus, there is a limit to widening the gain bandwidth by injecting more current into the bulk active layer and the quantum well active layer.
Decreasing a thickness of the bulk active layer or decreasing a layer number of the quantum well active layer decreases a state density of carriers per a unit area of the current injection region, whereby a Fermi level could be transferred to a higher energy side, and the gain bandwidth could be widened. However, even decreasing, e.g., a layer number of the quantum well active layer to one layer will widen the gain bandwidth to about 70 nm at maximum.
Here, a high reflection film (not shown) is formed on both side surfaces of the mesa-shaped light waveguide layer
138
to thereby form a semiconductor laser. However, the conventional semiconductor lasers using the balk active layer and the quantum well active have narrow gain bandwidths and accordingly narrow wavelength variable ranges.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a photosemiconductor device of a wide gain bandwidth, and a method for fabricating the photosmeiconductor device.
According to one aspect of the present invention, there is provided a photosemiconductor device comprising a plurality of quantum dots, the plurality of quantum dots having disuniform sizes.
According to another aspect of the present invention, there is provided a method for fabricating a photosemiconductor device comprising the step of: forming a plurality of quantum dots of disuniform sizes on a semiconductor substrate.
As described above, according to the present invention, the quantum dots of disuniform sizes are formed by a low area ratio, whereby the photosemiconductor device can have a wide gain bandwidth.
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patent: 09-082900 (1997-03-01), None
P. Borri et al.; “Time-Resolved Four-Wave Mixing in InAs/InGaAs Quantum-Dot Amplifiers Under Electrical Injection”, Applied Physics Letters, vol. 76, No. 11; Mar. 13, 2000, pp. 1380-1382.
Armstrong Westerman & Hattori, LLP
Meier Stephen D.
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