Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With heterojunction
Reexamination Certificate
1999-07-09
2001-05-01
Chaudhuri, Olik (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With heterojunction
C257S099000
Reexamination Certificate
active
06225648
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to light emitting diodes (LEDs), and more particularly to high-brightness LEDs.
BACKGROUND OF THE INVENTION
In U.S. Pat. No. 5,789,768 issued to Biing-Jye Lee et al., and assigned to the same assignee as the present application, a structure, as shown in
FIG. 1
, of a light emitting diode (LED) having high brightness is disclosed. In this structure, a semiconductor substrate
12
of n-type GaAs is formed on an n-type back electrode
10
, and a distributed Bragg reflector (DBR) layer
30
is formed on the semiconductor substrate
12
. AlGaInP or AlGaAs is preferably used in forming this DBR layer
30
. A stacked structure
14
is formed on the DBR layer
30
. The stacked structure
14
includes a bottom n-type cladding layer of AlGaInP
140
, an active layer of AlGaInP
142
, and a top p-type cladding layer of AlGaInP
144
. A p-type window layer
16
is formed on the top cladding layer
144
. Transparent material, such as GaP, GaAsP, GaInP or AlGaAs is preferably used to form the window layer
16
. A p-type contact layer
17
is formed on the window layer
16
. GaAsP, GaP, GaInP, or GaAs is preferably used to form the contact layer
17
. A transparent conductive layer
19
is formed on the contact layer
17
, extends into the central through hole of the contact layer
17
, and contacts with the window layer
16
. Tin oxide, indium oxide, or indium tin oxide (ITO) is preferably used to form the conductive layer
19
. A p-type front electrode
20
is formed on the conductive layer
19
.
This prior light emitting diode is characterized in that an ohmic contact is formed between the conductive layer
19
and the contact layer
16
, and the interface between the conductive layer
19
and the window layer
17
results in a Shottky barrier. Therefore, the current from the front electrode
20
spreads out in the conductive layer
19
, passes through the ohmic contact without passing through the Shottky barrier, and flows into the active layer
142
wherein it meets the current from the back electrode
10
and achieve the light emitting effect.
Although the current from the front electrode can be controlled to pass through the ohmic contact without passing through the Shottky barrier in this prior light emitting diode, part of the current will flow toward the location directly below the front electrode
20
when passing through the window layer
16
. This part of the current flows into the active layer
142
at the location directly below the electrode
20
, meets the current from the back electrode
10
there, and thereby results in light emitting effect. All of those who are skilled in the art know that the light emitted from the active layer at the location directly below the electrode
20
will be blocked by the electrode
20
and this will result in a low light emitting efficiency.
In the construction of the second embodiment disclosed in U.S. Pat. No. 5,153,889 issued to Hideto Sugawara et al., a current inhibiting layer is provided between a window layer and an upper clad layer to control the current distribution. However, the disadvantage of this prior light emitting diode lies in that it has to be formed in two epitaxial processes. More specifically, after forming the current inhibiting layer on the upper clad layer, the undesired portion of the current inhibiting layer has to be removed. After this, the second epitaxial process for forming the window layer can be carried out. The costs of equipment, manufacturing time, and yielding good products incurred by two epitaxial processes are much higher than those by a single epitaxial process.
SUMMARY OF THE INVENTION
To avoid the aforementioned disadvantages, it is an object of the invention to provide a high-brightness light emitting diode in which the current distribution in the active layer is under adequate control so that a better light emitting efficiency than the prior art can be achieved.
Another object of the present invention is to provide a high-brightness light emitting diode that only requires a single epitaxial process.
To achieve the above and other objects, a high-brightness light emitting diode is provided. It comprises a first electrode; a semiconductor substrate formed on the first electrode; a first cladding layer of a first conductivity type formed on the semiconductor substrate; an active layer formed on the first cladding layer; a second cladding layer of a second conductivity type formed on the active layer; a window layer of the second conductivity type formed on the second cladding layer and having an upper surface and a bottom surface, wherein a groove of a predetermined shape is formed at a predetermined location and substantially extends from the upper surface to the bottom surface so that the window layer is substantially separated into a first window portion and a second window portion and the current in the first window portion substantially cannot flow into the second window portion; a contact layer formed on the first window portion; a transparent conductive layer consisting of a first conductive portion and a second conductive portion, wherein the first conductive portion is formed on the contact layer and an ohmic contact is formed between the first conductive portion and the contact layer, the second conductive portion contacts with the surface of the groove and the upper surface of the second window portion, and a Schottky barrier is formed between the conductive portion and the window layer; and a second electrode formed on the conductive layer at a location over the second window portion.
REFERENCES:
patent: 5861636 (1999-01-01), Dutta et al.
patent: 6040590 (2000-03-01), OBrien et al.
Hsieh Min-Hsun
Jou Ming-Jiunn
Lee Biing-Jye
Chaudhuri Olik
Epistar Corporation
Hsu Winston
Wille Douglas A.
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