Active solid-state devices (e.g. – transistors – solid-state diode – Thin active physical layer which is – Heterojunction
Reexamination Certificate
2000-09-27
2002-07-16
Lee, Eddie (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Thin active physical layer which is
Heterojunction
C257S015000, C257S017000, C257S026000, C257S029000, C257S097000
Reexamination Certificate
active
06420727
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light-emitting semiconductor device with a quantum-wave interference layer which reflects carriers, i.e., electrons or holes, effectively, and with a quantum-wave interference layer which transmits carriers, i.e., electrons or holes, effectively. Especially, the present invention relates to a light-emitting semiconductor device such as a laser or a light-emitting diode with a structure which confines carriers in an emission layer so as to improve its luminous efficiency.
2. Description of the Related Art
A semiconductor device 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 having a multiple quantum well structure of a first and a second layer as a unit in a laser diode in order to reflect carriers 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.
SUMMARY OF THE INVENTION
The inventor of the present invention conducted a series of experiments and found that, although it can be understood that Takagi et al. used a band gap energy alternative to a kinetic energy, the suggested thickness 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. So a problem still persisted in inadequacy of reflecting carriers.
Further, the present inventor thought that multiple quantum-wave reflection of carriers might occur by a multiple layer structure with different band width, like multiple light reflection by a dielectric multi-film structure. And the inventor thought that it would be possible to confine carriers by the reflection of the quantum-wave interference layer and filed an application with respect to this (Japanese Patent Application laid-open No. H10-303406).
Then the inventor of the present invention concerned a characteristic of electrons as a wave and considered that the quantum-wave interference layer functions as a transmission layer of carriers, by analogy with the multiple reflection of the light. That is, when each thickness of layers in the multiple layer structure is about an order of the wavelength of a quantum-wave of carriers, an interference effect of quantum-wave is considered to occur with respect to a conduction of carriers in the multiple layer structure. The interference effect caused a conduction as a wave. Accordingly, the inventor of the present invention considered that not a conduction of particle in a classical theory but a resonance of waves, an interference, or other phenomenon is occurred by an interference effect of electrons. This wave behavioral characteristic of electrons improves a mobility and a propagation velocity.
Then the inventor of the present invention combined a reflection layer and a transmission layer of carriers and formed an emission layer between the reflection layer and the transmission layer in a light-emitting semiconductor device. Accordingly, the inventor of the present invention obtained a light-emitting semiconductor device having a completely new structure.
It is, therefore, an object of the present invention is to provide a semiconductor device with a new structure, having both a quantum-wave interference layer with a large reflectivity to carriers which functions as a reflection layer and a quantum-wave interference layer with a high transmittivity and a high mobility to carriers which functions as a transmission layer.
In light of these objects a first aspect of the present invention is a light-emitting semiconductor device constituted by a first 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, a second quantum-wave interference layer having plural periods of a pair of a third layer and a fourth layer, the fourth-layer having a wider band gap than the third layer, and an emission layer formed between the first and the second quantum-wave interference layers. Each thickness 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 carriers in each of the first and the second layers, each thickness of the third and the fourth layers in the second quantum-wave interference layer is determined by multiplying by an even number one fourth of a quantum-wave wavelength of carriers in each of the third and the fourth layers, and the thickness of the emission layer is determined by multiplying by an odd number one fourth of a quantum-wave wavelength of carriers in the emission layer. Here the emission layer formed between the first and the second quantum-wave interference layers may not contact to either the first or the second quantum-wave interference layers, or it may contact to both of the first and the second quantum-wave interference layers. Other semiconductor layers can exist at interfaces between the emission layer and the first quantum-wave interference layer and between the emission layer and the second quantum-wave interference layer.
A second aspect of the present invention is to form each thickness of the first and the second layers in the first quantum-wave interference layer by multiplying by an odd number one fourth of quantum-wave wavelength of carriers in each of the first and the second layers existing at the level near the lowest energy level of the second layer and to form each thickness of the third and the fourth layers in the second quantum-wave interference layer by multiplying an even number one fourth of quantum-wave wavelength of carriers in each of the third and the fourth layers existing at the level near the lowest energy level of the fourth layer. The thickness of the emission layer is determined by multiplying by an odd number one fourth of quantum-wave wavelength of carriers in the emission layer existing at the level near the lowest energy level of a layer which has a wider band gap and is adjacent to the emission layer. Here carriers transmit through the layer adjacent to the emission layer when the emission layer has a single layer structure, and when the emission layer has a single quantum well (SQW) structure or a multiple quantum well (MQW) structure, the layers adjacent to the emission layer are barrier layers formed on the both side of the emission layer.
A third aspect of the present invention is to form a &dgr;
R
layer, which varies an energy band sharply, at an interface between the first and the second layers. A thickness of the &dgr;
R
layer is substantially thinner than that of the first and the second layers.
A fourth aspect of the present invention is to form a &dgr;
T
layer, which varies an energy band sharply, at an interface between the third and the fourth layers. A thickness of the &dgr;
T
layer is substantially thinner than that of the third and the fourth layers.
A fifth aspect of the present invention is to define each thickness of the first and the second layers as follows:
D
RW
=n
RW
&lgr;
RW
/4
=n
RW
h
/4[2
m
RW
(
E
R
+V
R
)]
½
(1-1)
and
D
RB
=n
RB
&lgr;
RB
/4
=n
RB
h
/4(2m
RB
E
R
)
½
(1-2)
In Eqs. 1-1 and 1-2, h, m
RW
, m
RB
, E
R
, V
R
, and n
RW
, n
RB
represent Plank's constant, the effective mass of carriers in the first layer, the effec
Baumeister Bradley William
Canare Electric Co., Ltd.
Lee Eddie
LandOfFree
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