Active solid-state devices (e.g. – transistors – solid-state diode – Thin active physical layer which is – Heterojunction
Reexamination Certificate
1999-04-27
2001-09-25
Lee, Eddie (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Thin active physical layer which is
Heterojunction
C257S017000, C257S184000, C257S461000
Reexamination Certificate
active
06294795
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an opto-electric conversion device with a new structure, or a light-receiving device.
2. Description of the Related Art
A light-receiving device has been known to have a pin junction structure. A backward voltage is applied to the pin layers of the device, and electron-hole pairs are generated by that light incident from the side of a p-layer is absorbed in an i-layer. The electron-hole pairs excited in the i-layer are accelerated by a backward voltage in the i-layer, and electrons and holes are flowing into an n-layer and a p-layer, respectively. Thus a photocurrent whose intensity varies according to an intensity of the incident light is outputted.
To improve an opto-electric conversion effectivity, the i-layer which absorbs light is formed to have a comparatively larger thickness. But when the thickness of the i-layer becomes thicker, more times are needed to draw carriers to the n-layer and the p-layer. As a result, the response velocity of the opto-electric conversion is lowered. To improve the velocity, an electric field in the i-layer is increased by increasing a backward voltage. But when the backward voltage is enlarged, element separation becomes difficult and a leakage current occurs. As a result, a photocurrent which flows when light is not incident on the device, or a dark current, is increased.
Thus conventional light-receiving devices had an interrelation among a light-receiving sensitivity, a detecting velocity, and a noise current, which restricts their performances.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to improve the light-receiving sensitivity and the response velocity of the opto-electric conversion by providing a light-receiving device having a pin junction of a completely new structure.
In light of these objects a first aspect of the present invention is a light-receiving device, which converts incident light into electric current, constituted by quantum-wave interference layer units having plural periods of a pair of a first layer and a second layer, the second layer having a wider band gap than the first layer, and a carrier accumulation layer disposed between adjacent two of the quantum-wave interference layer units. Each thickness of the first and the second layers is determined by multiplying by an odd number one fourth of a quantum-wave wavelength of carriers in each of the first and the second layers, and the carrier accumulation layer has a band gap narrower than that of said second layer. Plural units of the quantum-wave interference layers are formed with a carrier accumulation layer, which has a band gap narrower than that of the second layer, lying between each of the quantum-wave interference units.
The second aspect of the present invention is to set a kinetic energy of the carriers, which determines the quantum-wave wavelength, at the level near the bottom of a conduction band when the carriers are electrons or at the level near the bottom of a valence band in the second layer when the carriers are holes.
The fourth aspect of the present invention is to define each thickness of the first and the second layers as follows:
D
W
=n
W
&lgr;
W
/4
=n
W
h/
4[2
m
W
(
E+V
)]
½
(1)
and
D
B
=n
B
&lgr;
B
/4
=n
B
h/
4(2
m
B
E
)
½
(2)
In Eqs. 1 and 2, h, m
W
, m
B
, E, V, and n
W
, n
B
represent Plank's constant, the effective mass of carrier conducting in the first layer, the effective mass of carriers in the second layer, the kinetic energy of the carriers at the level near the lowest energy level of the second layer, the potential energy of the second layer relative to the first layer, and odd numbers, respectively.
The fourth aspect of the present invention is a quantum-wave interference layer having partial quantum-wave interference layers I
k
with arbitrary periods T
k
including a first layer having a thickness of n
Wk
&lgr;
Wk
/4 and a second layer having a thickness of n
Bk
&lgr;
Bk
/4 for each of a plural different values E
k
, E
k
+V. E
k
, E
k
+V, &lgr;
Bk
, &lgr;
Wk
, and n
Bk
, n
Wk
represent a kinetic energy of carriers conducted in the second layer, a kinetic energy of carriers conducted in the first layer, a quantum-wave wavelength corresponding energies of the second layer and the first layer, and odd numbers, respectively.
The fifth aspect of the present invention is to form a carrier accumulation layer having the same bandwidth as that of the first layer.
The sixth aspect of the present invention is to form a carrier accumulation layer having a same thickness as its quantum-wave wavelength &lgr;
W
.
The seventh aspect of the present invention is to form a &dgr; layer between the first layer and the second layer, which sharply varies band gap energy at the boundary between the first and second layers and is substantially thinner than that of the first and the second layers.
The eighth aspect of the present invention is a light-receiving device having a pin junction structure, and the quantum-wave interference layer and the carrier accumulation layer are formed in the i-layer.
The ninth aspect of the present invention is to form the quantum-wave interference layer and the carrier accumulation layer in the n-layer or the p-layer.
The tenth aspect of the present invention is a light-receiving device having a pin junction structure.
First to Third, and Eighth to Tenth Aspects of the Invention
The principle of the light-receiving device of the present invention is explained hereinafter.
FIG. 1
shows an energy diagram of a conduction band and a valence band when an external voltage is applied to the interval between the p-layer and the n-layer in a forward direction. As shown in
FIG. 1
, the conduction band of the i-layer becomes plane by applying the external voltage. Four quantum-wave interference layer units Q
1
to Q
4
are formed in the i-layer, and carrier accumulation layers C
1
to C
3
are formed at each interval of the quantum-wave interference layer units.
FIG. 2
shows a conduction band of a quantum-wave interference layer unit Q
1
having a multi-layer structure with plural periods of a first layer W and a second layer B as a unit. A band gap of the second layer B is wider than that of the first layer W.
Electrons conduct from left to right as shown by an arrow in FIG.
2
. Among the electrons, those that exist at the level near the lowest energy level of a conduction band in the second layer B are most likely to contribute to conduction. The electrons near the bottom of the conduction band of the second layer B have a kinetic energy E. Accordingly, the electrons in the first layer W have a kinetic energy E+V which is accelerated by potential energy V due to the band gap between the first layer W and the second layer B. In other words, electrons that move from the first layer W to the second layer B are decelerated by potential energy V and return to the original kinetic energy E in the second layer B. As explained above, the kinetic energy of electrons in the conduction band is modulated by potential energy due to the multi-layer structure.
When thicknesses of the first layer W and the second layer B are equal to an order of the quantum-wave wavelength, electrons tend to have characteristics of a wave. The wave length of the electron quantum-wave is calculated by Eqs. 1 and 2 using kinetic energy of the electron. Further, defining the respective wave number vector of first layer W and second layer B as K
W
and K
B
, reflectivity R of the wave is calculated by:
R
=
(
&LeftBracketingBar;
K
W
&RightBracketingBar;
-
&LeftBracketingBar;
K
B
&RightBracketingBar;
)
/
(
&LeftBracketingBar;
K
W
&RightBracketingBar;
+
&LeftBracketingBar;
K
B
&RightBracketingBar;
)
=
(
[
m
W
(
E
+
V
)
]
1
/
2
-
[
m
B
E
]
1
/
2
)
/
(
[
m
W
(
E
+
V
)
]
1
/
2
+
[
m
B
E
]
1
/
2
)
=
[
1
-
(
m
B
E
/
m
W
(
E
+
V
)
)
1
/
2
]
/
[
1
+
(
m
B
E
/
m
W
(
E
+
V
Baumeister Bradley William
Canare Electric Co., Ltd.
Lee Eddie
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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