Active solid-state devices (e.g. – transistors – solid-state diode – Thin active physical layer which is – Heterojunction
Reexamination Certificate
1998-04-22
2001-02-13
Jackson, Jr., Jerome (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Thin active physical layer which is
Heterojunction
C257S021000, C257S186000, C257S438000
Reexamination Certificate
active
06188083
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pin diode having a new structure.
2. Description of the Related Art
Pin diodes having the same characteristic of rectification as pn diodes are known. Also known are avalanche diodes, Zener diodes, and Impact Avalanche Transit Time (IMPATT) diodes used by applying a backward voltage.
However, the I-V characteristics of these diodes have a problem in that they are difficult to change because they are determined by the semiconductor materials constituting the diodes. Therefore, further improvement is required.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to change the I-V characteristics when the backward voltage is applied to the pin diode.
The first aspect of the present invention is a diode constituted by a p-layer, an n-layer, and an i-layer sandwiched by the two layers and having a plurality of pairs of a first layer and a second layer, the second layer having a wider band gap than the first layer; wherein the thicknesses of the first and second layers are determined by multiplying by an odd number one fourth of the quantum-wave wavelength of carriers of at least one of electrons or holes, in each of the first and the second layers, injected into the i-layer.
The second aspect of the present invention is to set a kinetic energy of the carriers, which determines the quantum-wave wavelength, near the bottom of a conduction band when the carriers are electrons or near the bottom of a valence band in the second layer when the carriers are holes.
The third aspect of the present invention is a diode having a light receiver in a p-layer or an n-layer, which generates carriers injected into an i-layer.
The fourth aspect of the present invention is to form a &dgr; layer between the first layer and the second layer, which sharply varies in band gap energy from the first and second layers and has a thickness substantially thinner than that of the first and the second layers.
The fifth 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&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 the minority carriers injected into the first layer, the effective mass of the minority carriers in the second layer, the kinetic energy of the minority carriers injected into the second layer, being at the lowest energy level around the second layer, the potential energy of the second layer relative to the first layer, and odd numbers, respectively.
The sixth aspect of the present invention is to form a plurality of quantum-wave interference units in an i-layer in series, in series, each unit having a plurality of pairs of first and second layers.
The seventh aspect of the present invention is to form a carrier accumulation layer at interfaces of the quantum-wave interference units.
The diode having a structure of the present invention enables to vary the voltage at which electric current flows rapidly, and to change I-V characteristics in a step at several points. Further, the diode of the present invention can be used as a light-detecting diode.
(first, second and fifth aspects of the invention)
The principle of the quantum-wave interference layer of the present invention is explained hereinafter.
FIG. 1A
shows a conduction band of a quantum-wave interference layer formed in an i-layer. Electrons, or minority carriers, are injected into the i-layer, or conduct from left to right as shown by an arrow in
FIGS. 1A and 1B
. Among the electrons, those that exist near the bottom of the conduction band of the second layer B are 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 and are thus accelerated by the potential energy V due to the band gap difference 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 the potential energy V and return to their original kinetic energy E in the second layer B. As explained above, the kinetic energy of electrons in the conduction band is modulated by the potential energy due to the multi-layer structure.
When the thicknesses of the first layer W and the second layer B are on the 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 the kinetic energy of the electron. Further, defining the respective wave number vector of the first layer W and the 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
)
)
1
/
2
]
.
(
3
)
Further, when m
B
=m
W
, the reflectivity R is calculated by:
R=[
1−(
E/
(
E+V
))
½
]/[1+(
E/
(
E+V
))
½
(4).
When E/(E+V)=x, Eq. 4 is transformed into:
R=
(1
−x
½
)/(1+
x
½
) (5).
The characteristic of the reflectivity R with respect to the energy ratio x obtained by Eq. 5 is shown in FIG.
2
.
When the second layer B and the first layer W have S periods, the reflectivity R
S
on the incident face of a quantum-wave is calculated by:
R
S
=[(1−
x
S
)/(1+
x
S
)]
2
(6).
When the condition x≦{fraction (1/10)} is satisfied, R≧0.52. Accordingly, the relation between E and V is satisfied with:
E≦V/9 (7).
Since the kinetic energy E of the conducting electrons in the second layer B exists near the bottom of the conduction band, the relation of Eq. 7 is satisfied and the reflectivity R at the interface between the second layer B and the first layer W becomes 52% or more. Consequently, the multi-layer structure having two kinds of layers with band gaps different from each other enables effective quantum-wave reflection of electrons injected into the i-layer.
Further, utilizing the energy ratio x enables the thickness ratio D
B
/D
W
of the second layer B to the first layer W to be obtained by:
D
B
/D
W
=[m
W
/(
m
B
x
)]
½
(8).
As shown in
FIG. 1B
, when the backward voltage is applied to a diode having quantum-wave interference layer in the i-layer, the energy level of the quantum-wave interference layer band is inclined by the external voltage. Then E+V and E, or kinetic energy of the electrons in the first layer W and the second layer B respectively, increase according to a proceeding of quantum-wave. Accordingly, the thicknesses of the first layer W and the second layer B no longer improve the quantum-wave reflectivity of the electrons injected into the i-layer. Consequently, in the range of applied voltage for which the kinetic energy of electrons does not exceed the energy level used to design the thickness of the quantum-wave interference layer, the electrons are reflected and do not cause electric current. But when the applied voltage increases to the degree that the kinetic energy of the electrons injected into the i-layer exceeds the energy level used to design the thicknesses of the quantum-wave interference layer, reflected electrons begin to flow rapidly. Consequently, I-V characteristic of the diode varies rapidly. In short, the dynamic resistance of the diode drops.
The thicknesses of the first layer W and the second layer B
Baumeister Brad
Canare Electric Co., Ltd.
Jackson, Jr. Jerome
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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