Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Reexamination Certificate
2000-06-26
2002-08-20
Flynn, Nathan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
C257S448000, C257S459000
Reexamination Certificate
active
06437414
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical semiconductor device and a method for fabricating the optical semiconductor device, more specifically, an optical semiconductor device having the detection sensitivity increased and a method for fabricating the optical semiconductor device.
Infrared sensors of the quantum well type which are applicable to detection of two wavelengths of infrared radiation.
The conventional infrared sensor, i.e., the conventional optical semiconductor device will be explained with reference to
FIGS. 19A and 19B
.
FIG. 19B
is a plan view of one picture element of the conventional optical semiconductor device, which is on the side of the substrate of the sensor device.
FIG. 19A
is a sectional view along the line A-A′ in FIG.
19
B.
As shown in
FIG. 19A
, on the side of the substrate
116
, which is on the side of the sensor device substrate a picture element isolation insulation layer
118
is formed. A contact layer
120
is formed on the picture element isolation insulation layer
118
. An MQW (Multi Quantum Well) layer
126
is formed on the contact layer
120
. A contact layer
128
is formed on the MQW layer
126
.
On the contact layer
128
, an MQW layer
134
having different light absorbing characteristics from the MQW layer
126
is formed. A contact layer
136
is formed on the MQW layer
134
.
An insulation film
140
is formed on the contact layer
136
. An optical coupling layer
144
is formed in stripes on the insulation film
140
.
A mirror electrode
164
is formed on the upper surface and the side surface of the optical coupling layer
144
formed in stripes. The mirror electrode
164
and the optical coupling layer
144
make up an optical coupler. Light incident on the side of the substrate
116
is scattered by the optical coupler to be absorbed by the MQW layers
126
,
134
.
In such optical semiconductor device, an opening
200
and an opening
202
are formed from the upper surface of the mirror electrode
164
respectively down to the contact layer
120
and the contact layer
128
. The openings
200
,
202
are diverged gradually from the contact layers
120
,
128
to the mirror layer
164
. A picture element isolation groove
166
for isolating each picture element is formed down to the picture element isolation insulation film
118
. An insulation film
168
is formed on the entire surface.
Contact holes are further formed in the bottoms of the openings
200
,
202
, arriving at the contact layers
120
,
128
. Ohmic electrodes
162
c
,
162
a
are formed respectively on the contact layers
120
,
128
in the contact holes.
As shown in
FIG. 19B
, three connection electrodes
114
a
,
114
b
,
114
c
are formed in a cylindrical shape outside the openings
200
,
202
. The connection electrodes
114
a
,
114
b
,
114
c
are to be connected to a reading circuit substrate (not shown) for reading detected signals.
The connection electrode
114
a
is connected by a line
206
to the ohmic electrode
162
a
formed on the contact layer
128
. The connection electrode
114
c
is connected by a line
204
to the ohmic electrode
162
c
formed on the contact layer
120
. The connection electrode
114
b
is connected to an ohmic electrode
162
b
formed on the contact layer
136
.
The mirror electrode
164
is formed on the entire surface, interrupted around the connection electrodes
114
a
,
114
b
,
114
c
for the prevention of short-circuit among the connection electrodes
114
a
,
114
b
,
114
c.
In such optical semiconductor device, a direct-current bias is applied from the side of the reading circuit substrate via the connection electrode
114
a
. An output of the MQW layer
134
is supplied to the reading circuit substrate via the connection electrode
114
b
. An output of the MQW layer
126
is supplied to the reading circuit substrate via the connection electrode
114
c.
However, in the conventional optical semiconductor device, the openings
200
,
202
are formed large, and especially the opening
200
arriving at the lower MQW layer
126
is made larger, which makes an area of the optical coupler and an area of the MQW layers
126
,
134
accordingly small. That is, a light-receptive area of the optical semiconductor device of such structure is too small to obtain sufficient sensitivity.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical semiconductor device having improved optical detection sensitivity and a method for fabricating the optical semiconductor device.
The above-described object is achieved by an optical semiconductor device comprising: a first contact layer formed on a substrate; a first quantum well layer formed on the first contact layer; a second contact layer formed on the first quantum well layer; an optical coupling layer formed on the second contact layer; and a first conductor plug extended from an upper surface of the optical coupling layer and arriving at the first contact layer. The contact layers and the connection electrodes are connected to each other respectively by the conductor plugs. The conductor plugs have such small sectional areas that the quantum well layers can secure sufficiently large areas. Accordingly, high sensitivity can be provided. Upper portions of the conductor plugs are also etched in stripes, and can function as an optical coupler, whereby light can be scattered, with a result of increased sensitivity. The conductor plugs are buried in the contact holes, whereby the connection electrodes can be formed on the conductor plugs. Accordingly, higher freedom of design can be obtained in arranging the connection electrodes.
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patent: 4894526 (1990-01-01), Bethea et al.
patent: 5023685 (1991-06-01), Bethea et al.
patent: 5223704 (1993-06-01), Hui et al.
patent: 5318666 (1994-06-01), Elkind et al.
patent: 5506419 (1996-04-01), Levine et al.
patent: 5532173 (1996-07-01), Martin et al.
patent: 6184538 (2000-02-01), Bandara et al.
patent: 63-246626 (1963-10-01), None
patent: 2-43777 (1990-02-01), None
Matsukura Yusuke
Nishino Hironori
Tanaka Hitoshi
Yokoyama Mitsunori
Armstrong Westerman & Hattori, LLP
Flynn Nathan
Fujitsu Limited
Quinto Kevin
LandOfFree
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