Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With heterojunction
Reexamination Certificate
2002-03-05
2003-07-15
Wilson, Allan R. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With heterojunction
C257S096000
Reexamination Certificate
active
06593597
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Taiwan application serial no. 90113545, filed Jun. 5, 2001.
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a light-emitting diode (LED). More particularly, the present invention relates to a group III-V element-based light-emitting diode with electrostatic discharge (ESD) protection capacity.
2. Description of Related Art
In recent years, group III-V nitride-based semiconductor materials have been used to produce light in the blue and ultraviolet range as well as high-temperature electronic devices. The material is quite versatile in the opto-electronic field. In particular, the group III-V group nitride-based semiconductor materials such as GaN, GaAlN, InGaN are suitable for fabricating light-emitting diodes.
FIG. 1
is a schematic cross-sectional view of a conventional light-emitting diode constructed using group III-V nitride semiconductor material.
As shown in
FIG. 1
, the light-emitting diode is formed over a transparent substrate such as an aluminum oxide (Al
2
O
3
) layer. A nucleation layer
12
and an n-type conductive buffer layer
14
are sequentially formed over the substrate
10
. The n-type buffer layer
14
, for example, can be an n-doped gallium nitride (GaN) that facilitates subsequent crystal growth. A light-emitting active layer
18
is formed above the buffer layer
14
. In general, a confinement layer or cladding layer
16
and
20
are formed, one above the active layer
18
and one below the active layer
18
. The upper and the lower confinement layers (
16
and
20
) are doped using dopants of opposite polarity. In
FIG. 1
, the lower confinement layer
16
is an n-doped aluminum-gallium-nitride (AlGaN) layer while the upper confinement layer
20
is a p-doped aluminum-gallium-nitride (AlGaN) layer. A contact layer
22
is also formed over the upper confinement layer
20
. The contact layer
22
can be a p-type gallium nitride (GaN) layer, for example. An electrode
24
serving as an anode of a diode is formed over the contact layer
22
. In addition, another electrode
26
that serves as a cathode of the diode is formed over the buffer layer
14
in a region isolated from the lower confinement layer
16
, the active layer
18
and the upper confinement layer
20
.
FIG. 2A
is a schematic circuit diagram showing a silicon-based shunt diode connected in parallel with a light-emitting diode (LED) to protect the LED against damages due electrostatic discharge. To prevent any damages to the light-emitting diode
30
due to electrostatic discharge (ESD) during operation, a silicon diode
40
is connected in parallel with the LED
30
. Since the silicon diode
40
operates in the breakdown region, the diode
40
is always in a conductive state. If a normal forward bias voltage is applied to the two terminals V+ and V− of the LED
30
, carrier passing through the p-n junction of the LED
30
produces a forward current that generates light. When an abnormal reversed voltage appears or there is an electrostatic discharge, excess voltage is discharged through the diode
40
operating in the breakdown mode. Since the discharge path goes through the second diode
40
instead of going through the LED
30
, the LED
30
will not be damaged due to the presence of an abnormal voltage or electromagnetic discharge, which would causes the unrecoverable damage.
FIG. 2B
is a schematic cross-sectional view of the LED in
FIG. 2A
with a silicon diode. According to the conventional method, the LED system is implemented using a flip-chip structure. As shown in
FIG. 2B
, the light emitting diode
30
includes a transparent substrate
32
, an n-doped gallium nitride (GaN) layer
34
, a p-doped gallium nitride (GaN) layer
36
and a pair of electrodes
38
a
and
38
b
. The diode
40
includes an n-doped silicon layer
42
, a p-doped silicon layer
44
and a pair of metallic layers
46
a
and
46
b.
Areas
50
a
and
50
b
contain solder material. Through the solder material, the p-doped silicon layer
44
is electrically coupled to the n-doped gallium nitride layer
34
and the n-doped silicon layer
42
is electrically coupled to the p-doped gallium nitride layer
36
. Thus, the structural layout shown in
FIG. 2B
produces the equivalent circuit shown in FIG.
2
A.
A forward bias voltage is applied to the V+ terminal and the V− terminal in a normal operation. Hence, current flows from the p-doped gallium nitride layer
36
to the n-doped gallium nitride layer
34
so that generated light passes through the transparent substrate
32
. When an abnormal reversed voltage appears or there is an electrostatic discharge, discharge current will pass from the n-doped silicon layer
42
to the p-doped silicon layer
44
without going through the main body of the light-emitting diode
30
.
Although the aforementioned system is capable of minimizing damages to the light-emitting diode that result from an electrostatic discharge, the structure is difficult to manufacture. As shown in
FIG. 2B
, the light-emitting diode
30
section of the structure has to flip over the silicon diode. Not only is the structure difficult to fabricate, but mass production is also costly. Moreover, any deviation from alignment during package may result in a lower light-emitting power or device failure.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a group III-V element-based light-emitting diode structure having electrostatic discharge protection capacity. The structure includes a reverse bias operating diode formed on the same side of a transparent substrate as the light-emitting diode so that manufacturing is simplified.
A second object of the present invention is to provide a group III-V element-based light emitting diode having a flip-chip structure and electrostatic discharge protection capacity. The structure incorporates a Schottky diode or a shunt diode so that electrostatic discharge protection capacity is enhanced.
A third object of the present invention is to provide a group III-V element-based light emitting diode having a flip-chip structure and electrostatic discharge protection capacity. The structure not only reduces processing steps, but also increases light-emitting power of the light-emitting diode.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a group III-V element-based light emitting diode having electrostatic discharge protection capacity. The structure includes a transparent substrate, a nucleation layer, a conductive buffer layer, a first confinement layer, an active layer, a second confinement layer, a contact layer, a first electrode, a second electrode, a third electrode and a fourth electrode. The nucleation layer is formed over the transparent substrate. The nucleation layer is a composite layer that includes a first nucleation layer and a second nucleation layer. The first nucleation layer and the second nucleation layer are isolated from each other. Similarly, the conductive buffer layer is a composite layer that includes a first conductive buffer layer and a second conductive buffer layer. The first conductive buffer layer and the second conductive buffer layer are formed over the first nucleation layer and the second nucleation layer, respectively. The first confinement layer, the active layer, the second confinement layer and the contact layer are formed over the first conductive buffer layer.
The first confinement layer is above the first conductive buffer layer and both layers are doped identically. The active layer is above the first confinement layer. The active layer is a semiconductor material layer containing doped group III-V nitride-based materials. The second confinement layer is above the active layer. The second confinement layer contains dopants that are different from the dopants in the first confinement layer. The contact layer is above the second confinement laye
J. C. Patents
South Epitaxy Corporation
Wilson Allan R.
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