Active solid-state devices (e.g. – transistors – solid-state diode – Thin active physical layer which is – Heterojunction
Reexamination Certificate
2000-10-25
2002-11-05
Lee, Eddie (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Thin active physical layer which is
Heterojunction
C257S013000, C257S014000, C257S015000, C257S191000
Reexamination Certificate
active
06476412
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device having quantum-wave interference layers that reflect carriers, or electrons and holes, effectively. In particular, the invention relates to light-emitting semiconductor devices including a laser (LD) and a light-emitting diode (LED) with improved luminous efficiency by effectively confining carriers within an active layer. Further, the present invention relates to semiconductor devices including a field effect transistor (FET) and a solar cell with improved carrier reflectivity.
2. Description of the Related Art
An LD has been known to have a double hetero junction structure whose active layer is formed between n-type and p-type cladding layers. The cladding layers function as potential barriers for effectively confining carriers, or electrons and holes, within the active layer.
However, a problem persists in luminous efficiency. Carriers overflow the potential barriers of the cladding layers, which lowers luminous efficiency. Therefore, further improvement has been required, as presently appreciated by the present inventors.
As a countermeasure, forming cladding layers with a multi-quantum well structure of a first and a second layers as a unit 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 values of kinetic energy of carriers to be considered and the degree of luminous intensity improvement 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 confine electrons, 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 quantum-wave reflection of carriers might occur by a multi-layer structure with different band width, like multiple light reflection by a dielectric multi-film structure. And the inventors thought that it would be possible to confine carriers by the reflection of the quantum-wave. As a result, the inventors invented a preferable quantum-wave interference layer and applications of the same.
It is, therefore, a first object of the present invention to provide a quantum-wave interference layer, with high reflectivity to carriers, functioning as a reflecting layer. It is a second object of the present invention to improve quantum-wave reflectivity by additionally providing a new layer structure with a multi-layer structure whose band width is different with respect to each other. It is a third object of the invention to provide variations of a quantum-wave interference layer for effectively reflecting quantum-waves.
In light of these objects a first aspect of the present invention is a semiconductor device constituted by a quantum-wave interference layer 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. 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 existing around the lowest energy level of the second layer.
The second aspect of the present invention is a semiconductor device constituted by a quantum-wave interference layer having plural periods of a first layer and a second layer as a unit. The second layer has a wider band gap than the first layer. A &dgr; layer is included for sharply varying an 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 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
)]
1/2
(1)
and
D
B
=n
B
&lgr;
B
/4
=n
B
h
/4(2
m
B
E
)
1/2
(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 carrier in the first layer, effective mass of carrier 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 semiconductor device 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
)]
1/2
(3)
and
D
Bk
=n
Bk
&lgr;
Bk
/4
=n
Bk
h
/4(2
m
Bk
E
k
)
1/2
(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 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 semiconductor device 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 second layers.
The seventh aspect of the present invention is a semiconductor device having a quantum-wave interference layer constituted by a plurality of semiconductor layers made of a hetero-material with different band gaps. The interference layer is constituted by a plurality of &dgr; layers for sharply varying the energy band and being formed at an interval of one forth of a quantum-wave wavelength of carriers multiplied by an odd number. The thickness of the &dgr; layers is significantly thinner than the width of the interval.
When a single level E of kinetic energy is adopted, the interval DB between the &dgr; layers is calculated by Eq. 2. When plural levels E
k
of kinetic energy are adopted, the interval D
Bk
between the &dgr; layers are calculated by Eq. 4. In the latter case, several partial quantum-wave interference layers I
k
with the &dgr; layers formed at an interval D
Bk
in T
k
periods may be arranged in series from I
1
to I
j
to form a quantum-wave interference layer as a whole. Alternatively, the partial quantum-wave interference layer may be formed by serial S layers with intervals of D
B1
, . . . , D
Bk
, . . . , to D
Bj
, and the plurality of the partial quantum-wave interference layers may be arranged in series with an arbitrary period.
The eighth aspect of the present invention is to use the quantum-wave interference layer as a reflecting layer for reflecting carriers.
The ninth aspect of the present invention is to constitute a quantum-wave incident facet in the quantum-wave i
Baumeister Bradley W.
Canare Electric Co., Ltd.
Lee Eddie
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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