Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With particular semiconductor material
Utility Patent
1998-08-10
2001-01-02
Meier, Stephen D. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With particular semiconductor material
C257S105000, C257S186000
Utility Patent
active
06169298
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to a semiconductor light emitting device, and more particularly, to a semiconductor light emitting device using an electrically conductive oxide as a transparent window layer.
BACKGROUND OF THE INVENTION
The basic principle of the light emitting diode is released light when a electron and a hole are coupled. In the PN junction, electrons and holes are injected into P and N areas respectively under forward bias. These carries of electrons and holes in the depletion region of the PN junction are recombined and the energy is released in the form of light.
The conventional light emitting AlGaInP that is double heterostructure includes an n-type GaAs substrate, a lower n-type AlGaInP cladding layer formed on the top of the substrate, an AlGaInP active layer formed on the cladding layer, and an upper p-type AlGaInP cladding layer formed on the active layer. The light emitting devices are applied to fabricate the light emitting diode in visible wavelength between 680 nm and 550 nm while changing the ratio of aluminum and gallium in the active layer. The cladding layers can confine the carriers in the active layer to increase light emitting efficiency.
In recent years, many investigations into improving the structure and technology are proposed to increase the brightness and efficiency of the light emitting diode. For example, a conductive window layer is formed on the top of the double heterostructure to increase the current spreading. The conventional double heterostructure in the active layer is replaced by a multi-layer quantum well structure to increase the brightness of the light emitting diode and for smoothing the linear relation between light emitting power and current.
In the prior art, U.S. Pat. No. 5,008,718 a light emitting diode is proposed (see particularly FIG.
1
). The structure of the proposed light emitting diode is consists of an n-type GaAs substrate
10
, a lower n
5
type AlGaInP cladding layer
11
, an undoped AlGaInP active layer
12
, a upper p-type AlGaInP cladding layer
13
, a window layer
14
, a back electrode
15
, and a front electrode
16
. The basic feature of the patent is to form a window layer of low resistivity, excellent conductivity, and having an energy band gap greater than the energy band gap of the active layer on the top of p-type AlGaInP cladding layer to reduce the current crowding effect.
Suitable materials for producing a window layer are AlGaAs, GaAsP, and GaP, wherein the lattice parameter of the AlGaAs that is used to fabricating the light emitting diode in the wavelength from the red to the yellow region is lattice matched with the GaAs substrate. The GaAsP and GaP with greater energy band gap are suitable to fabricate a window layer of the light emitting diode in the region of shorter wavelength. The disadvantage of the materials lattice mismatched with the substrate effect the operation life of the device. The device is grown by two steps. First, the AlGaInP double heterostructure is formed by metalorganic vapor phase epitaxy (MOVPE) second, a thick window layer is formed on the DH structure by vapor phase epitaxy (VPE). However, this method increases the process complexity and the time required for fabricating the device.
Referring to
FIG. 2
, due to the fact that the energy band gap of a GaAs substrate is smaller than the energy band gap of the AlGaInP active layer, the light released from a active layer will be adsorbed almost by the GaAs substrate. U.S. Pat. No. 5,376,580 has proposed another structure to increase the light emitting efficiency. The structure includes an n-type GaP substrate
20
, a n-type lower AlGaInP cladding layer
21
, an undoped AlGaInP active layer
22
, a p-type upper AlGaInP cladding layer
23
, a p-type GaP window layer
24
, a front electrode
25
, and a back electrode
26
. The feature is to etch the GaAs substrate like as the structure of the light emitting diode in
FIG. 1
by chemical etching, leaving an epitaxy layer having a thickness of about 50 &mgr;m. Bonding a GaP substrate having a thickness of about 350 &mgr;m to the epitaxy layer by wafer bonding technology forms a AlGaInP light emitting diode having a transparent substrate. However, the method must result in a thin film of 50 &mgr;m and avoid to breaking the film, the yield is not good due to process difficulties.
One of the references related to the light emitting diode can be seen in U.S. Pat. No. 5,481,122. Referring to
FIG. 3
of that patent, the same layers can be seen in
FIG. 1
with the same labels. The feature of the patent in the GaP window layer is replaced by a p-type contact layer
31
and a conductive oxide window layer
32
, wherein GaAsP, GaP, or GaAs is used to form the p-type contact layer
31
. The oxide for forming the transparent window layer
32
could be tin oxide, indium oxide, or indium tin oxide (ITO). The transmittance is about 90% for light wavelength in the visible region. Furthermore, the electrical resistivity is only about 3×10
−4
&OHgr;-cm, that is a thousandth resistivity of the p-type AlGaInP and a hundredth resistivity of the p-type GaP.
In view of the present situation, a need has arisen to develop a semiconductor light emitting device for increasing output power, and furthermore, to overcome the disadvantages of the conventional approaches.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a high efficiency semiconductor light emitting device.
Another object of the present invention is to provide a high efficiency semiconductor light emitting device having an electrically conductive oxide layer as a transparent window layer.
According to the invention, a semiconductor light emitting device comprises:
a substrate consisting of a GaAs substrate and a GaAsP layer;
a light emitting layer comprising a first cladding layer, an active layer and a second cladding; and
a windowing layer forming of AlZnO(x) material.
A semiconductor light emitting device, such as the light emitting diode (LED) or the laser diode (LD), includes a first conductivity type GaAs substrate and a first conductivity type GaAsP layer which is formed on the top of the substrate to increase the band gap energy of the substrate. A first conductivity type distributed Bragg reflector layer is formed on the GaAsP layer. An AlGaInP double heterostructure including a first cladding AlGaInP layer of the first conductivity type, an undoped active AlGaInP layer, and a second cladding AlGaInP layer of the second conductivity type is grown on the top of the distributed Bragg reflector layer. The undoped active AlGaInP layer can also be replaced by a multi-layer quantum well structure of AlGaInP. A second conductivity type layer of low energy band gap and high conductivity material is formed on the AlGaInP double heterostructure. A AlZnO(x) window layer of the second conductivity type is then formed on the top of the low energy band gap layer.
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patent: 5563422 (1996-10-01), Nakamura et al.
patent: 5614734 (1997-03-01), Guido
patent: 5739553 (1998-04-01), Noto et al.
patent: 5760422 (1998-06-01), Ishinaga
Chang Liang-Tung
Cheng Shiang-Peng
Kuo Kuan-Chu
Lin Chiao-Yun
Lin Ying-Fu
Harness & Dickey & Pierce P.L.C.
Kingmax Technology Inc.
Meier Stephen D.
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