GaN based group III-V nitride semiconductor light-emitting...

Details GaN based group III-V nitride semiconductor light-emitting... GaN based group III-V nitride semiconductor light-emitting...

2001-12-12

2003-12-02

Pham, Long (Department: 2814)

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

Incoherent light emitter structure

With housing or contact structure

C257S079000, C257S082000, C257S083000, C257S089000, C257S093000, C257S098000, C257S103000

Reexamination Certificate

active

06657237

ABSTRACT:

Priority is claimed to Patent Application Numbers 2000-77746, filed in the Republic of Korea on Dec. 18, 2000 and 2001-4035 filed in Republic of Korea on Jan. 29, 2001, herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor light-emitting device and a method for fabricating the same, and more particularly, to a GaN based Group III-V nitride semiconductor light-emitting device and a method for fabricating the same.
2. Description of the Related Art
Compound semiconductor based light-emitting diodes or laser diodes capable of emitting short-wavelength visible light are widely known. In particular, a light-emitting device (light-emitting diode) or laser diode fabricated using a Group III nitride semiconductor has received considerable attention because the Group III nitride semiconductor is a direct transition type material (direct bandgap material) emitting blue light at high efficiencies by the recombination of electrons and holes.
Referring to
FIG. 1
, a conventional light-emitting diode (LED) based on GaN based III-V nitrides includes an n-type GaN layer
12
on a sapphire substrate
10
. The n-type GaN layer
12
is divided into first and second regions R
1
and R
2
. The first region R
1
has a larger width then the second region R
2
and is not affected by etching after having been formed. Meanwhile, the second region R
2
is thinner than the first region R
1
because it is affected by etching after having been formed. As a result, there exists a step between the first and second regions R
1
and R
2
of the n-type GaN layer
12
. An active layer
16
, a p-type GaN layer
18
, and a light-transmitting p-type electrode
20
are sequentially formed on the first region R
1
in the n-type GaN layer
12
. A pad layer
22
for use in bonding in a packaging process is formed on the light-transmitting p-type electrode
20
. An n-type electrode
14
is formed in the second region R
2
of the n-type GaN layer
12
.
In
FIG. 2
, a conventional GaN based III-V nitride semiconductor laser diode in which n-type and p-type electrodes are arranged to face the same direction, and a ridge is formed in a region where the p-type electrode is formed, is shown. In the semiconductor laser diode, In particular, referring to
FIG. 2
, an n-type GaN layer
12
, which is divided into first and second regions R
1
and R
2
, is formed on a sapphire substrate
10
. The first region R
1
is wider and thicker than second region R
2
so that there exists a step between the first and second regions R
1
and R
2
. An n-type electrode
14
is formed in the second region R
2
of the n-type GaN layer
12
. An n-type AlGaN/GaN layer
24
, an n-type GaN layer
26
, and an InGaN layer
28
acting as an active layer, for which the refractive index increasingly higher in the upward direction, are sequentially formed on the first region R
1
of the n-type GaN layer
12
. A p-type GaN layer
30
, a p-type AlGaN/GaN layer
32
, and a p-type GaN layer
36
, for which the refractive index is increasingly lower in the upward direction, are sequentially formed on the InGaN layer
28
. The p-type AlGaN/GaN layer
32
has a ridge (or rib) at the center thereof, and the p-type GaN layer
36
is formed on the ridge of the p-type AlGaN/GaN layer
32
. The entire surface of the p-type AlGaN/GaN layer
32
is covered with a passivation layer
34
. Here, the passivation layer
34
extends to the p-type GaN layer
36
such that the current threshold is reduced. That is, the passivation layer
34
covers both edges of the p-type GaN layer
36
. A p-type electrode
38
is formed on the passivation layer
34
in contact with a top surface of the p-type GaN layer
36
, which is not covered by the passivation layer
34
.
For a conventional light-emitting diode or laser diode based on a GaN based III-V nitride semiconductor in which the n-type and p-type electrodes are arranged to face the same direction, a bonding process with two wires should be performed on the same plan in a packaging process. Thus, the packaging process is complex and increases time consumption. The n-type electrode is formed in a deeply etched region so that a large step exists between the n-type and p-type electrodes, thereby increasing failure in packaging processes. As described with reference to
FIGS. 1 and 2
, in terms of the structure of the second region R
2
of the n-type GaN layer
12
, the n-type GaN layer
12
is etched to form the second region R
2
, for the light-emitting diode of
FIG. 1
, after the formation of the p-type electrode
20
or the p-type GaN layer
18
, and for the laser diode of
FIG. 2
, after the formation of the p-type AlGaN/GaN layer
32
. In other words, to form the h-type electrode
14
on the second region R
2
, an additional photolithography process is required, thereby increasing the manufacturing time of light-emitting devices.
FIG. 3
shows another conventional GaN based III-V nitride semiconductor laser diode in which an n-type electrode and a p-type electrode are arranged to face opposite directions with an active layer therebetween. An n-type GaN layer
12
, an n-type AlGaN/GaN layer
24
, an n-type GaN layer
26
, an InGaN layer
28
acting as an active layer, a p-type GaN layer
30
, a p-type AlGaN/GaN layer
32
, and a p-type GaN layer
36
, a passivation layer
34
, and a p-type electrode
38
are sequentially formed on a silicon carbide (SiC) substrate
10
a
(or a gallium nitride (GaN) substrate). An n-type electrode
14
a
is formed on the bottom of the SiC substrate
10
a.
In general, the current threshold and the lasing mode stability for laser emission in semiconductor laser diodes are closely associated with temperature, and all quantal properties degrade as the temperature rises. Therefore, there is a need to dissipate heat generated in an active layer during laser emission to prevent a temperature rise in the laser diode. For the conventional GaN based III-V semiconductor laser diode, the substrate has a very low thermal conductivity (about 0.5 W/CmK for sapphire) so that the heat is dissipated mostly through the ridge. However, heat dissipation through the ridge is limited so that a temperature rise in laser diodes cannot be prevented effectively, thereby lowering the properties of devices.
For the conventional semiconductor laser diode shown in
FIG. 2
, it has been intended to dissipate heat generated in the active layer by applying a flip chip bonding technique, as illustrated in FIG.
4
.
In particular, referring to
FIG. 4
, reference character A denotes the inverted conventional GaN based III-V semiconductor laser diode shown in FIG.
2
. Reference numeral
40
denotes a submount, reference numerals
42
a
and
42
b
denote pad layers, reference numerals
44
a
and
44
b
denote first and second thermal conductive layers connected to an n-type electrode
14
and a p-type electrode
38
, respectively, of the semiconductor laser diode A. Reference character M denotes a stack of material layers corresponding to the material layers
24
through
34
of
FIGS. 2 and 3
stacked between the n-type GaN layer
12
and the p-type electrode
38
.
As described above, heat dissipation efficiency can be improved by bonding a semiconductor laser diode to a separate heat dissipating assembly. However, bonding between the laser diode and the heat dissipating assembly increases the overall processing time. In addition, such a bonding process needs to follow a fine alignment between the semiconductor laser diode and the heat dissipating assembly, so that failure is more likely to occur, thereby lowering yield.
For example, assuming that the yield is 70%, about 4,000 pieces of laser diodes per wafer are obtained. A bonding time required for flip-chip bonding of all the laser diodes amounts about 20 hours (about 0.3 minutes each).
SUMMARY OF THE INVENTION
To solve the above-described problems, it is a first object of the present invention to provide a GaN based III-V nitride semiconductor light-emitting device which a photolithography pro

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