Active solid-state devices (e.g. – transistors – solid-state diode – Thin active physical layer which is – Heterojunction
Reexamination Certificate
1999-10-22
2002-11-26
Lee, Eddie (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Thin active physical layer which is
Heterojunction
C257S014000, C257S015000, C257S017000, C257S097000
Reexamination Certificate
active
06486490
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a light-emitting device having at least two pairs of a quantum-wave interference layer that effectively reflects carriers, or electrons and holes, respectively. 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 with an active layer.
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 to reflect carriers 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 confine electrons, and that preferable thickness of the first and second layers are 4 to 6 times larger than those suggested by Takagi et al.
Further, the present inventor thought that multiple quantum-wave reflection of carriers might occur by a multi-layer structure with different band width, like multiple light reflection by dielectric multi-film structure. And the inventor 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 an LED in which an emission layer is sandwiched by quantum-wave interference layers with high reflectivity to carriers, functioning as reflecting layers. It is a second object of the present invention is to improve a luminous efficiency of an electron-hole pair by forming an emission layer sandwiched by quantum-wave interference layers in an LED having an emission layer in a p-layer.
In light of these objects a first aspect of the present invention is an LED constituted by two pairs of quantum-wave interference layers Each having plural periods of a pair of a first layer and a second layer as a unit. The second layer has a wider band gap than the first layer. The LED has at least a p-layer and an n-layer, and an emission layer is formed in the p-layer. The emission layer is sandwiched by two pairs of quantum-wave interference layers. Each thicknesses of the first and the second layers in the first quantum-wave interference layer is determined by multiplying by an odd number one fourth of a quantum-wave wavelength of electrons in each of the first and the second layers, and each thicknesses of the first and the second layers in the second quantum-wave interference layer is determined by multiplying by an odd number one fourth of a quantum-wave wavelength of holes in each of the first and the second layers.
The second aspect of the present invention is the LED constituted by the first and the second quantum-wave interference layers each having plural periods of a first layer and a second layer as a unit. Electrons which determine thicknesses of the first and the second layers formed in the first quantum-wave interference layer exists around the lowest energy level of the second layer.
The third aspect of the present invention is the LED constituted by the first and the second quantum-wave interference layers each having plural periods of a first layer and a second layer as a unit. Holes which determine thicknesses of the first and the second layers formed in the second quantum-wave interference layer exists around the lowest energy level of the second layer.
The fourth aspect of the present invention is to define each thicknesses of the first and the second layers in at least one of the first and the second quantum-wave interference layer 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 fifth aspect of the present invention is an LED having a plurality of partial quantum-wave interference layers I
k
, formed in at least one of the first and the second quantum-wave interference layer, 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 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 sixth aspect of the present invention is an LED having a plurality of partial quantum-wave interference layers arranged in series with arbitrary periods, formed in at least one of the first and the second quantum-wave interference layer. 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 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, in at least one of the first and the second quantum-wave interference layer.
The eighth aspect of the present invention is to use at least one of the first and the second 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 at least one of the first and the quantum-wave interference layer by a second layer with enough thickness for preventing minority carriers from being injected into the first layer by a tunneling effect.
(First to Fourth Aspects of the Present Invention)
The principle of the quantum-wave interference layer of the present invention is explained hereinafter. First, the first quantum-wave interference layer, or an electron reflecting layer which reflects electrons, is explained.
FIG. 1
shows a conduction band of a multi-layer str
Baumeister Bradley William
Canare Electric Co., Ltd.
Lee Eddie
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