Active solid-state devices (e.g. – transistors – solid-state diode – Heterojunction device – Field effect transistor
Reexamination Certificate
1999-10-22
2002-11-12
Lee, Eddie (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Heterojunction device
Field effect transistor
C257S015000, C257S017000, C257S020000
Reexamination Certificate
active
06479842
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a field effect transistor (FET) having quantum-wave interference layers that reflect carriers, or electrons and holes, effectively. In particular, the invention relates to field effect transistors including a metal semiconductor field effect transistor (MESFET) having a Schottky junction structure, a metal oxide semiconductor field effect transistor (MOSFET), and a high electron mobility transistor (HEMT) in which carriers are effectively confined in a channel region and used effectively by reflecting the carriers to prevent them from leaking to other region.
2. Description of the Related Art
Plural MOSFETs on a large-scale integrated (LSI) circuit have been known little to have a method to avoid leakage current from a source (S) into the drains (D′) of other transistor. Because voltage is applied to gate regions sandwiching a channel (C) region, impurities are doped to the lower gate region of a semiconductor which is used to form a MOSFET. As a result, the method to avoid leakage current is considered to be difficult.
As a countermeasure, reflecting carriers by forming cladding layers with a multi-quantum well structure of a first and a second layers as a unit in a laser diode (LD) has been suggested by Takagi et al. (Japanese Journal of Applied Physics. Vol.29, No.11, November 1990, pp.L1977-L1980). Although it can be led that a band gap energy is used as an alternative of a kinetic energy, this reference does not teach or suggest values of kinetic energy of carriers to be considered and the degree of luminous intensity improvement is inadequate.
SUMMARY OF THE INVENTION
The inventor 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 dielectic multi-film structure. And the inventors thought that it would be possible to increase threshold of the external voltage at which a current starts to flow 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, an object of the present invention to provide a field effect transistor having a novel junction structure with considerably larger threshold of voltage at which a current starts to flow by forming a quantum-wave interference layer in a lower gate region adjacent to a channel.
In light of these objects a first aspect of the present invention is a field effect transistor comprising a quantum-wave interference layer having plural periods of a pair of a first layer and a second layer in a region adjacent to a channel, 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 carriers in each of the first and the second layers, which exist around the lowest energy level of the second layer.
The second aspect of the present invention is a field effect transistor comprising a quantum-wave interference layer having plural periods of a pair of a first layer and a second layer as a unit in a region adjacent to a channel. 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 is determined by multiplying by an odd number one fourth of quantum-wave wavelength of 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 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 a Plank's constant, effective mass of carriers in the first layer, effective mass of carriers in the second layer, kinetic energy of carriers at the lowest energy level around the second layer, potential energy of the second layer to the first layer, and odd numbers, respectively.
The fourth aspect of the present invention is a field effect transistor 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 carriers flowing into the second layer, effective mass of minority carriers with kinetic energy E
k
+V in the first layer, effective mass of 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 fifth aspect of the present invention is a transistor 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
Wj
, 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 sixth 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 seventh aspect of the present invention is to use the quantum-wave interference layer as a reflecting layer for reflecting carriers.
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 carriers by a tunneling effect.
First and Third Aspects of the Present Invention
The principle of the quantum-wave interference layer of the present invention is explained hereinafter. The quantum-wave interference layer is formed in, i.e., a p-layer, which is formed beneath an inversion layer of a field effect transistor.
FIG. 1
shows a conduction band of a quantum-wave interference layer 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 a first layer. In a channel, electrons as minority carriers flow from a source to a drain. Electrons which leak to the p-layer formed beneath the channel, conduct from left to right as shown by an arrow in FIG.
1
. Among the electrons, those that existing 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,
Baumeister Bradley Wm.
Canare Electric Co., Ltd.
Lee Eddie
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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