Active solid-state devices (e.g. – transistors – solid-state diode – Thin active physical layer which is – Heterojunction
Reexamination Certificate
1998-04-09
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
C257S009000, C257S012000, C257S014000, C257S015000
Reexamination Certificate
active
06188082
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a diode having a structure with whose dynamic resistance lowered.
2. Description of the Related Art
A diode which has a pn junction has been known. Electric current, which flows when the forward voltage is applied to the diode, increases rapidly at the point where the forward voltage exceeds the potential difference between the conduction bands of p and n layers. The larger gradient of the characteristic curve between electric current and voltage in the dynamic range is, the more suitable the diode becomes to use as various devices.
However, a problem persists in the gradient. The gradient of electric current and voltage characteristics could not be varied because it is determined by materials which form the diode. Therefore, further improvement has been required, as presently appreciated by the present inventors.
As a countermeasure, reflecting carriers by forming cladding layers with multi-quantum well structure of a series of a pair of a first and a second layers has been suggested by Takagi et al. (Japanese Journal of Applied Physics. Vol. 29, No. 11, November 1990, pp. L1977-L1980). This reference, however, does not teach or suggest the values of the kinetic energy of carriers to be considered and the degree of reflectivity of carriers is inadequate.
SUMMARY OF THE INVENTION
The inventors of the present invention conducted a series of experiments and found that the suggested thicknesses of the first and the second layers by Takagi et al. were too small to reflect carriers, and that preferable thicknesses of the first and second layers are 4 to 6 times larger than those suggested by Takagi et al. Further, the present inventors thought that multiple reflection of quantum-waves of carriers might occur by a multi-layer structure with different band width, like multiple reflection of light by a dielectric multi-film structure. And the inventors thought that it would be possible to vary the V-I characteristic of carriers when the external voltage is applied to the diode by the quantum-wave reflection. As a result, the inventors invented a preferable quantum-wave interference layer and applications of the same.
It is, therefore, the object of the present invention to provide a diode with considerably lower dynamic resistance by forming a quantum-wave interference layer in a p-layer or an n-layer.
In the light of the object a first aspect of the present invention is a diode constituted by forming a quantum-wave interference layer having plural periods of a pair of a first layer and a second layer in at least one of a p-layer and an n layer, the second layer having a wider band gap than the first layer. Each thickness of the first and the second layers is determined by multiplying by an odd number one fourth of quantum-wave wavelength of injected minority carriers in each of the first and the second layers.
The second aspect of the present invention is a diode constituted by a quantum-wave interference layer having plural periods of a pair of a first layer and a second layer. The second layer has a wider band gap than the first layer. A &dgr; layer is included for sharply varying energy band and is formed between the first and the second layers. Each thickness of the first and the second layers in the p-layer or the n-layer is determined by multiplying by odd number one fourth of quantum-wave wavelength of injected minority carriers in each of the first and the second layers, and a thickness of the &dgr; layer is substantially thinner than that of the first and the second layers.
The third aspect of the present invention is a diode having injected carriers existing around the lowest energy level of the second layer.
The fourth aspect of the present invention is to define each thickness of the first and 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 a plank constant, effective mass of minority carrier injected into the first layer, effective mass of minority carriers in the second layer, kinetic energy of minority carriers injected into the second layer, potential energy of the second layer to the first layer, and odd numbers, respectively. And minority carrier injected into the second layer is preferably exist around the lowest energy level of the second layer.
The fifth aspect of the present invention is a diode having a plurality of partial quantum-wave interference layers I
k
with arbitrary periods T
k
including a first layer having a thickness of D
Wk
and a second layer having a thickness of D
Bk
and arranged in series. The thicknesses of the first and the second layers satisfy the formulas:
D
Wk
=n
Wk
&lgr;
Wk
/4
=n
Wk
h
/4[2
m
Wk
(E
k
+V)]
½
(3)
and
D
Bk
=n
Bk
&lgr;
Bk
/4
=n
Bk
h
/4(2
m
Bk
E
k
)
½
(4).
In Eqs. 3 and 4, E
k
, m
Wk
, m
Bk
, and n
Wk
and n
Bk
represent plural kinetic energy levels of minority carriers injected into the second layer, effective mass of minority carriers with kinetic energy E
k
+V in the first layer, effective mass of minority carriers with kinetic energy E
k
in the second layer, and arbitrary odd numbers, respectively.
The plurality of the partial quantum-wave interference layers I
k
are arranged in series from I
1
to I
j
, where j is a maximum number of k required to form a quantum-wave interference layer as a whole.
The sixth aspect of the present invention is a diode having a quantum-wave interference layer with a plurality of partial quantum-wave interference layers arranged in series with arbitrary periods. Each of the plurality of partial quantum-wave interference layers is constructed with serial pairs of the first and second layers. The widths of the first and second layers of the serial pairs are represented by (D
W1
, D
B1
), . . . , (D
Wk
, D
Bk
), . . . , (D
Bj
, D
Bj
). (D
Wk
, D
Bk
) is a pair of widths of the first and second layers and is defined as Eqs 3 and 4, respectively.
The seventh aspect of the present invention is to form a &dgr; layer between a first layer and a second layer which sharply varies the energy band and has a thickness substantially thinner than that of the first and the second layers.
The eighth aspect of the present invention is to constitute a quantum-wave incident facet in the quantum-wave interference layer by a second layer with enough thickness for preventing conduction of minority carriers injected into the first layer by a tunneling effect.
(first and fourth aspects of the invention)
The principle of the quantum-wave interference layer of the present invention is explained hereinafter.
FIG. 1
shows a conduction band of a multi-layer structure, formed in a p-layer, with plural periods of a pair of a first layer W and a second layer B. A band gap of the second layer B is wider than that of the first layer W. Electrons, or minority carriers, which have been injected into the p-layer, conduct from left to right as shown by an arrow in FIG.
1
. Among the electrons, those that exist around the bottom of the second layer B are likely to contribute to conduction. The electrons around the bottom of the second layer B has 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, 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 order of a quantum-wave wavelength, electrons tend to have characteristics of a wave. The wav
Baumeister Bradley William
Canare Electric Co., Ltd.
Jackson, Jr. Jerome
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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