Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – In combination with or also constituting light responsive...
Reexamination Certificate
2001-03-29
2002-08-13
Ho, Hoai V. (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
In combination with or also constituting light responsive...
C257S076000, C257S087000
Reexamination Certificate
active
06433364
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an AlGaInP-based compound semiconductor light emitting device formed on a GaP substrate.
Semiconductor elements using AlGaInP based semiconductor materials have been used as light emitting devices in a visible area since they allows lattice-matching with a GaAs substrate and have a largest direct transition band gap among III-V group compound semiconductors. In particular, as light-emitting devices, the semiconductor elements using AlGaInP based semiconductor materials perform direct transition-type light emission in the range from 550 nm to 690 nm, which brings about high light emitting efficiency. However, when the GaAs substrate is used, they serve not as a transparent layer but as a photoabsorption layer against a radiation light. Consequently, in the case where plane emission-type AlGaInP based semiconductor elements are used, high luminance can not be achieved.
To solve this problem, there has been proposed an architecture in which an AlGaInP based semiconductor light emitting device is placed not on the GaAs substrate but on a GaP substrate transparent against a radiation light of the AlGaInP based semiconductor element (as shown in Japanese Patent Laid-Open Publication No. 2714885).
The following description discusses the AlGaInP based semiconductor light emitting device formed on the GaP substrate with reference to FIG.
10
. The AlGaInP based semiconductor light emitting device formed on the GaP substrate is formed through the following steps.
First, as shown in
FIG. 10A
, an AlGaInP clad layer
2
, an AlGaInP active layer
3
, and an AlGaInP clad layer
4
are formed in sequence on a GaAs substrate
1
by a MOCVD (metal-organic chemical vapor deposition) method. Next, as shown in
FIG. 10B
, a GaP layer
5
is formed by a LPE (liquid-phase epitaxy) process utilizing yo-yo solute supply method or temperature difference method. Then, as shown in
FIG. 10C
, the GaAs substrate
1
, which serves as a photoabsorption layer, is removed. After the GaAs substrate
1
is removed, a GaP current diffusion layer
6
is formed on the AlGaInP clad layer
2
by the LPE process utilizing yo-yo solute supply method or temperature difference method. Through the steps stated above, an AlGaInP based semiconductor light emitting device is formed on the GaP layer
5
as a substrate.
In the AlGaInP based semiconductor light emitting device formed on the GaP substrate shown in
FIGS. 10A
to
10
D, current is diffused by the GaP current diffusion layer
6
and light is emitted in the wide range of the active layer
3
, which results in increased light emitting efficiency. In addition, the GaP layer
5
and the GaP current diffusion layer
6
are larger in the band gap than the AlGaInP active layer
3
, so that the emitted light is transmitted without being absorbed, which implements high light emitting efficiency.
However, the prior art AlGaInP based semiconductor light emitting device formed on the GaP substrate has a problem stated below. That is, as large as four steps are required to produce an AlGaInP based semiconductor light emitting device. More particularly, AlGaInP based light emitting portions
2
to
4
are formed on a GaAs substrate
1
in the first production step, a GaP layer
5
is formed thereon by the LPE process utilizing yo-yo solute supply method or temperature difference method in the second step, the GaAs substrate
1
is removed by etching in the third step, and thereafter a GaP current diffusion layer
6
is formed by the LPE process utilizing yo-yo solute supply method or temperature difference method in the fourth step. This causes substantial increase of the production costs.
Further, the GaAs substrate
1
is used and removed in the production process, which causes further increase of the production costs.
Accordingly, in order to avoid the step of removing the GaAs substrate
1
, an inventor made a trial of creating the AlGaInP based light emitting portions and the GaP current diffusion layer directly on the GaP substrate by the MOCVD method. In this case, the AlGaInP based semiconductor light emitting device can be produced by one growth step so that the GaAs substrate is not necessary, which enables substantial decrease of the production costs. However, the result of the trail disclosed that the AlGaInP based light emitting portions having lattice mismatch are created on the GaP substrate, and further thereon the GaP current diffusion layer having lattice mismatch is created, so that crystallinity of the GaP current diffusion layer is degraded, which creates uneven surface and generates a number of crystal defects.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a semiconductor light emitting device, enabling substantial decrease of the production costs, having a good crystalline current diffusion layer, and implementing considerable increase of light emitting efficiency.
In order to achieve the above object, there is provided a semiconductor light emitting device comprising: a light emitting portion made up of at least an active layer and clad layers; and a current diffusion layer formed above a GaP substrate,
wherein the current diffusion layer is defined as In
x
Ga
1−x
P(0<X<1) where a composition ratio of In equals to X.
According to the above structure, the In
x
Ga
1−x
P current diffusion layer formed on top of the layers has the In composition ratio X equal to (0<X<1) Consequently, the uneven depth of the crystal surface is considerably diminished, and the crystal defect concentration is substantially decreased. As a result, a current diffusion layer with good crystallinity can be obtained. In addition, In
x
Ga
1−x
P is used as the current diffusion layer, so that in the case where the active layer is composed of an AlGaInP based semiconductor, the light emitted in the active layer is absorbed neither by the GaP substrate nor by the current diffusion layer, which implements substantial improvement of light emitting efficiency. Further, the light emitting device can be produced simply by forming each layer in sequence on the GaP substrate, which contributes to reduction of the production costs.
Also, there is provided a semiconductor light emitting device comprising: a light emitting portion made up of at least an active layer and clad layers; and a current diffusion layer formed above a GaP substrate,
wherein the current diffusion layer is defined as In
x
Al
y
Ga
1−x−y
P (0<x<1, 0<y<1) where a composition ratio of In equals to x and a composition ratio of A1 equals to y.
According to the above structure, the In
x
Al
y
Ga
1−x−y
P current diffusion layer formed on top of the layers has the In composition ratio x equal to (0<X<1). Consequently, the uneven depth of the crystal surface is considerably diminished, and the crystal defect concentration is substantially decreased. As a result, a current diffusion layer with good crystallinity can be obtained. In the case where the band gap is decreased by increasing the value of the In composition ratio x for improving the crystallinity, the band gap of the current diffusion layer can be increased without degrading the crystallinity by the step of increasing the value of the A1 composition ratio y. Accordingly, when the active layer is made up of an AlGaInP based semiconductor, the light emitted in the active layer is not absorbed in the current diffusion layer, which implements substantial improvement of light emitting efficiency. Further, the light emitting device can be produced simply by forming each layer in sequence on the GaP substrate, which contributes to reduction of the production costs.
In one embodiment of the present invention, a normal of the GaP substrate surface inclines with respect to a normal of a (100) plane toward a [011] direction.
According to the above structure, the normal of the GaP substrate surface inclines with respect to the normal of the (100) plane toward the [011] direction, so that d
Hosoba Hiroyuki
Kurahashi Takahisa
Murakami Tetsurou
Nakatsu Hiroshi
Ho Hoai V.
Huynh Andy
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