Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Reexamination Certificate
2001-03-28
2002-04-30
Jackson, Jr., Jerome (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
C257S465000, C257S021000, C257S184000
Reexamination Certificate
active
06380604
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
The present application is based on Japanese priority applications No. 2000-146849 and 2000-336066 respectively filed on May 18, 2000 and Nov. 2, 2000, the entire contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The present invention generally relates to semiconductor devices and more particularly to a quantum semiconductor device having quantum dots. Further, the present invention relates to optical detectors and optical memory devices that use such quantum dots.
In the field of optical telecommunication, various optical detectors are used for detecting optical signals transmitted through an optical fiber. Such optical detectors include high-speed PIN photodiodes. With recent increase of signal traffic in such optical telecommunication systems, on the other hand, there is a demand for faster optical detectors that are capable of operating with low power consumption and high photosensitivity.
In order to deal with sharply increasing optical traffic in such optical telecommunication systems, the use of so-called wavelength-multiplexing technology is spreading in the art of optical telecommunication. In such a wavelength-multiplexing technology, there is a demand for optical detectors that are capable of tuning to various optical wavelengths.
Conventionally, photodiodes having a p-n junction or a pin junction have been used extensively in optical telecommunication systems for high-speed detection of optical signals.
FIG. 1
shows the construction of a typical conventional p-n junction photodiode
10
.
Referring to
FIG. 1
, the photodiode
10
is constructed on a substrate
11
of n-type InP, and includes a buffer layer
12
of n-type InP formed on the substrate
11
, an optical absorption layer
13
of n
−
-type InGaAs formed on the buffer layer
12
, and a p
+
-type region
13
A of InGaAs formed inside the optical absorption layer
13
, wherein the optical absorption layer
13
carries thereon an electrode
14
in correspondence to the p
+
-type region
13
A. Further, a ring-shaped electrode
16
having an opening acting as an optical window is provided on a bottom principal surface of the InP substrate
11
. Further, the exposed top surface of the optical absorption layer
13
is protected by an SiN passivation film
15
. A photodiode having a pin junction also has a similar structure.
In view of the fact that the photodiode
10
of
FIG. 1
has a planar construction, it is necessary in such a photodiode
10
to introduce incoming optical radiation over a substantial area in order to detect the optical current with sufficient S/N ratio. In other words, the photodiode
10
of
FIG. 1
has a drawback of low sensitivity.
In the photodiode
10
of
FIG. 1
, it is possible to reduce the optical power needed for the photodiode to carry out the photodetection, by decreasing the optical area, in other words the area of the p
+
-type region
13
A. However, such a decrease of the optical area is limited by the photolithographic process, and there arises a problem in that the photodiode
10
having the planar structure suffers from the problem of low sensitivity of photodetection.
In the field of information technology, on the other hand, there is occurring a sharp increase of data to be processed, and there is growing a need for a high-speed, large-capacity memory device for dealing with such large amount of data. When such a high-speed, large-capacity memory device is to be realized by a conventional semiconductor memory device, there arises a need of providing a very complex wiring pattern, and the complexity of the wiring pattern increases with increasing integration density of the semiconductor memory device. Associated therewith, it is expected that various problems, such as signal delay, decrease of yield and increase of cost, would be caused when such a memory device is constructed by conventional semiconductor memory devices.
In this regard, optical semiconductor memory devices that are written with information by a feeble optical signal are expected as being a device capable of overcoming the foregoing problems of semiconductor memory devices. By using optical semiconductor memory devices, it is expected to carry out writing and reading of information directly by an optical beam that can carry a large amount of information.
Conventionally, there is proposed a photo-electron integrated device that uses discrete energy levels characteristic to quantum dots for detection of optical signals as described in the Japanese Laid-Open Patent Publication 8-32046. According to this prior art, a number of quantum dots are formed in a planar structure and the quantum dots are used for optical detection, optical modulation, or optical output of wavelength-multiplex optical signals.
In such optical signal-processing device that uses quantum dots, it is necessary to form each of the quantum dots such that the quantum dot is tuned to the wavelength of the optical signal component to be detected. However, it is extremely difficult to form the desired quantum dots with necessary precision, quality and yield as long as conventional patterning process is used. Further, it is difficult to form the quantum dots with necessary size.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of the present invention to provide a novel and useful quantum semiconductor device wherein the foregoing problems are eliminated.
Another and more specific object of the present invention is to provide a high-sensitivity optical detector.
Another object of the present invention is to provide an optical semiconductor memory device that is capable of being written with information by a feeble optical beam.
Another object of the present invention is to provide a quantum semiconductor device having quantum dots wherein the energy level of the quantum dots can be controlled as desired.
Another object of the present invention is to provide a spectrum analyzer that uses a quantum semiconductor device including therein quantum dots.
Another object of the present invention is to provide an optical receiver of wavelength-multiplex optical signals for selectively detecting an optical signal component in an incoming wavelength-multiplex optical signal.
Another object of the present invention is to provide a semiconductor optical detector, comprising:
a first semiconductor layer having a first conductivity type;
a second semiconductor layer formed on said first semiconductor layer;
a third semiconductor layer formed on said second semiconductor layer, said third semiconductor layer having said first conductivity type;
a pyramidal pit formed in said third semiconductor layer so as to invade into said second semiconductor layer, said pyramidal pit being defined by a plurality of facets merging together at an apex located in said second semiconductor layer in the vicinity of an interface to said first semiconductor layer, said apex being located with an offset from said interface;
a channel layer covering said plurality of facets continuously in said pyramidal pit, said channel layer having said first conductivity type;
a barrier layer formed in said pyramidal pit so as to cover said channel layer;
a cap layer formed in said pyramidal pit so as to cover said barrier layer;
an optical window formed on said cap layer;
a first electrode formed on said third semiconductor layer; and
a second electrode formed on said first semiconductor layer.
Another object of the present invention is to provide a semiconductor optical detector, comprising:
a substrate having a first conductivity type;
a first semiconductor layer formed on said substrate, said first semiconductor layer having said first conductivity type;
a second semiconductor layer formed on said first semiconductor layer;
a third semiconductor layer formed on said second semiconductor layer, said third semiconductor layer having said first conductivity type;
a pyramidal pit formed in said third semiconductor layer so as to invade into said second semiconductor layer, said pyramidal pi
Armstrong Westerman & Hattori, LLP
Fujitsu Limited
Jackson, Jr. Jerome
LandOfFree
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