Group III nitride compound semiconductor light-emitting element

Details Group III nitride compound semiconductor light-emitting element Group III nitride compound semiconductor light-emitting element

2002-06-06

2003-11-18

Lebentritt, Michael S. (Department: 2824)

Active solid-state devices (e.g., transistors, solid-state diode

Heterojunction device

Light responsive structure

C257S188000, C257S079000, C257S088000, C257S089000, C257S086000, C257S087000

Reexamination Certificate

active

06649943

ABSTRACT:

This is a patent application based on a Japanese patent application No. 2001-171870 which was filed on Jun. 7, 2001 and which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a Group III nitride compound semiconductor light-emitting element containing a plurality of low-energy-band-gap layers which emit light of different wavelengths.
2. Background Art
In order to attain mass production of, for example, white LEDs, many studies have heretofore focused on semiconductor light-emitting elements containing a plurality of low-energy-band-gap layers which emit light of different wavelengths.
FIG. 13
shows energy band diagrams of conventional semiconductor light-emitting elements, each containing two low-energy-band-gap layers which emit light of different wavelengths.
FIG. 13A
shows an energy band diagram of a semiconductor light-emitting element containing two low-energy-band-gap layers which emit light of wavelengths that are arbitrarily or appropriately different, and containing no quantum-barrier-formation barrier layer between the low-energy-band-gap layers.
FIG. 13B
shows an energy band diagram of a semiconductor light-emitting element containing two low-energy-band-gap layers which emit light of wavelengths that are arbitrarily or appropriately different, and containing a simple quantum-barrier-formation barrier layer between the low-energy-band-gap layers.
As shown in
FIG. 13A
, when no quantum-barrier-formation barrier layer is provided between the two low-energy-band-gap layers, electrons and holes tend to migrate to the layer having lower band gap energy; i.e., the layer which emits light of long wavelength. Therefore, difficulty is encountered in “obtaining a desired ratio of emission intensity between the low-energy-band-gap layers”; for example, causing the two low-energy-band-gap layers to emit at substantially the same intensity. Therefore, a desired light color is difficult to obtain by mixing emitted light of different colors.
As shown in
FIG. 13B
, when a simple barrier layer is provided between the two low-energy-band-gap layers, electrons are easily distributed to one of the low-energy-band-gap layers and holes are easily distributed to the other. Therefore, even when a desired emission intensity ratio is obtained, emission efficiency is lowered at the two low-energy-band-gap layers. That is, the resultant semiconductor element fails to exhibit sufficient emission intensity and emission efficiency.
As shown in
FIGS. 13A and 13B
, when overflow of carriers is effectively prevented by increasing energy barriers of p-type and n-type semiconductor layers provided on the two low-energy-band-gap layers, the p-type and n-type semiconductor layers must be increased in thickness, and the semiconductor layers must also be increased in aluminum (Al) content. As a result, the semiconductor element is prone to cracking.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide a semiconductor light-emitting element containing a plurality of low-energy-band-gap layers which emit light of different wavelengths, which easily attains “desired proportions in emission intensity between the low-energy-band-gap layers” and which exhibits excellent emission efficiency and durability.
In order to achieve the above object, the present invention employs the following means.
According to first means of the present invention, there is provided a Group III nitride compound semiconductor light-emitting element formed of Group III nitride compound semiconductor layers, comprising multiple layers containing light-emitting layers (hereinafter collectively called “a multi-layer containing light-emitting layers” or “a multi-layer”), a p-type semiconductor layer, and an n-type semiconductor layer, wherein the multi-layer comprises a multiple quantum barrier-well layer containing quantum-barrier-formation barrier layers formed from a Group III nitride compound semiconductor and quantum-barrier-formation well layers formed from a Group III nitride compound semiconductor, the barrier layers and the well layers being laminated alternately and cyclically, and a plurality of low-energy-band-gap layers which emit light of different wavelengths; and the multiple quantum barrier-well layer is provided between the low-energy-band-gap layers. Here “low-energy band gap layer” also includes a well layer.
As used herein, the expression “Group III nitride compound semiconductor” encompasses binary, ternary, and quaternary semiconductors of arbitrary compositional proportions represented by the following formula: Al
x
Ga
y
In
(1−x−y)
N (0≦x≦1, 0≦y≦1, 0≦x+y≦1); and semiconductors containing trace amounts or small amounts of p-type or n-type impurities, the impurities having substantially no effect on the compositional proportions x and y.
Therefore, the expression “Group III nitride compound semiconductor” encompasses binary and ternary Group III nitride compound semiconductors, such as AlN, GaN, InN, AlGaN of arbitrary or appropriate compositional proportions, AlInN of arbitrary or appropriate compositional proportions, and GaInN of arbitrary or appropriate compositional proportions; and semiconductors containing trace amounts or small amounts of p-type or n-type impurities, the impurities having substantially no effect on the compositional proportions.
The expression “Group III nitride compound semiconductor” encompasses semiconductors in which the aforementioned Group III element (Al, Ga, or In) is partially substituted by boron (B) or thallium (Tl), or in which nitrogen (N) is partially substituted by phosphorus (P), arsenic (As), antimony (Sb), or bismuth (Bi).
Examples of the aforementioned p-type impurity include magnesium (Mg) and calcium (Ca).
Examples of the aforementioned n-type impurity include silicon (Si), sulfur (S), selenium (Se), tellurium (Te), and germanium (Ge).
These impurities may be incorporated in combination of two or more species, and a p-type impurity and an n-type impurity may be incorporated in combination.
The aforementioned low-energy-band-gap layer may have an SQW structure or an MQW structure.
FIG. 1
illustrates the function of a multiple quantum barrier-well layer employed in the present invention.
FIG. 1A
shows an energy band diagram of the multiple quantum barrier-well layer. In
FIG. 1A
, reference letter Wb represents the thickness of a quantum-barrier-formation barrier layer constituting the multiple quantum barrier-well layer, Ww represents the thickness of a quantum-barrier-formation well layer constituting the multiple quantum barrier-well layer, and Vb represents the energy level of the quantum-barrier-formation barrier layer.
When electrons are applied to the multiple quantum barrier-well layer from the left side of the drawing as shown in
FIG. 1A
, the probability that the electrons are reflected to the left side (i.e., reflectance) is classically thought to be as shown in FIG.
1
B. In
FIGS. 1B and 1C
, reference letter E on the x-axis represents the kinetic energy of electrons applied in a forward direction.
However, in reality, electrons behave on the basis of the quantum theory. Therefore, by virtue of the tunnel effect or interference of electronic waves, the reflectance of electrons to the multiple quantum barrier-well layer substantially corresponds to the results of a quantum-theoretical simulation shown in FIG.
1
C. In
FIG. 1C
, me (=0.2) represents the ratio of the effective mass of conduction electrons to the rest mass of electrons in the multiple quantum barrier-well layer, the ratio being employed in the simulation.
When “d” represents the length of ½ the lamination cycle of each of the quantum-barrier-formation barrier layers constituting the multiple quantum barrier-well layer (2.5 nm in the case shown in
FIG. 1
) and “&lgr;” represents the wavelength of conduction electrons injected to the multiple quantum barrier-well layer, conduction electrons satisfying the following rel

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