Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With housing or contact structure
Reexamination Certificate
2002-09-17
2004-06-01
Pham, Long (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With housing or contact structure
C257S094000, C257S103000
Reexamination Certificate
active
06744075
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a nitride-based semiconductor light-emitting device and a method of forming the same, and more particularly, it relates to a nitride-based semiconductor light-emitting device including an electrode layer and a method of forming the same.
2. Description of the Background Art
A nitride-based semiconductor laser element, which is an exemplary nitride-based semiconductor light-emitting device, is expected as the light source for an advanced large capacity optical disk and actively developed nowadays. In order to reduce the operating voltage of the nitride-based semiconductor laser element and improve reliability thereof, the contact resistance of electrodes must essentially be reduced. In particular, a nitride-based semiconductor has a low p-type carrier concentration and hence it is difficult to obtain an excellent ohmic property (low contact resistance) in relation to a p-side electrode. In order to cope with this, a Pd-based electrode material such as a Pd/Au electrode or a Pd/Pt/Au electrode containing Pd having an excellent ohmic property has been recently employed as the p-side electrode.
FIG. 28
is a sectional view showing a conventional nitride-based semiconductor laser element
150
having a Pd-based electrode. The structure of the conventional nitride-based semiconductor laser element
150
is now described with reference to FIG.
28
. In the conventional nitride-based semiconductor laser element
150
, an AlGaN low-temperature buffer layer
102
having a thickness of about 15 nm is formed on a sapphire substrate
101
. An undoped GaN layer
103
having a thickness of about 3 &mgr;m is formed on the AlGaN low-temperature buffer layer
102
. An n-type GaN contact layer
104
is formed on the undoped GaN layer
103
with a thickness of about 5 &mgr;m. An n-type AlGaN cladding layer
105
having a thickness of about 1 &mgr;m, an MQW (multiple quantum well) emission layer
106
of InGaN having a thickness of about 50 nm and a p-type AlGaN cladding layer
107
of about 300 nm in thickness having a projection portion are formed on the n-type GaN contact layer
104
. A p-type GaN contact layer
108
having a thickness of about 70 nm is formed on the projection portion of the p-type AlGaN cladding layer
107
.
A p-side electrode
109
consisting of a Pd-based electrode having a three-layer structure of a Pd layer of about 10 nm in thickness, an Au layer of about 100 nm in thickness and an Ni layer of about, 200 nm in thickness in ascending order is formed on the p-type GaN contact layer
108
. An SiO
2
film
110
is formed to cover regions other than part of the upper surface of the p-side electrode
109
and the upper surface of the n-type GaN contact layer
104
. A pad electrode
111
is formed to cover the SiO
2
film
110
while coming into contact with the upper surface of the p-side electrode
109
.
Partial regions of the layers from the p-type AlGaN cladding layer
107
to the n-type GaN contact layer
104
are removed. An n-side electrode
112
is formed to be in contact with an exposed part of the upper surface of the n-type GaN contact layer
104
. A pad electrode
113
is formed to be in contact with the n-side electrode
112
.
FIGS. 29
to
33
are sectional views for illustrating a process of fabricating the conventional nitride-based semiconductor laser element
150
having the Pd-based electrode shown in FIG.
28
.
FIG. 34
is a sectional view showing the conventional nitride-based semiconductor laser element
150
shown in
FIG. 28
in a state mounted on a submount
170
from the side of an active layer in a junction-up system. The fabrication process for the conventional nitride-based semiconductor laser element
150
having the Pd-based electrode is now described with reference to
FIGS. 28
to
34
.
First, the AlGaN low-temperature buffer layer
102
is grown on the sapphire substrate
101
by MOCVD under a low temperature condition of about 600° C. in order to relax lattice mismatching, as shown in FIG.
29
. The undoped GaN layer
103
is formed on the AlGaN low-temperature buffer layer
102
with the thickness of about 3 &mgr;m by MOCVD.
Thereafter the n-type GaN contact layer
104
having the thickness of about 5 &mgr;m, the n-type AlGaN cladding layer
105
having the thickness of about 1 &mgr;m, the MQW emission layer
106
having the thickness of about 50 nm, the p-type AlGaN cladding layer
107
having the thickness of about 300 nm and the p-type GaN contact layer
108
having the thickness of about 70 nm are successively formed on the undoped GaN layer
103
by MOCVD.
Then, partial regions of the layers from the p-type GaN contact layer
108
to the n-type GaN contact layer
104
are removed by anisotropic dry etching, as shown in FIG.
30
.
Then, the Pd layer of about 10 nm in thickness, the Au layer of about 100 nm in thickness and the Ni layer of about 200 nm in thickness are formed in ascending order in a striped shape of about 2 &mgr;m in width by a lift off method or the like, thereby forming the p-side electrode
109
consisting of the Pd-based electrode having the three layer structure of the Pd layer, the Au layer and the Ni layer as shown in FIG.
31
. Thereafter the uppermost Ni layer of the p-side electrode
109
is employed as an etching mask for etching the p-type GaN contact layer
108
by anisotropic dry etching employing CF
4
gas while etching the p-type AlGaN cladding layer
107
by about 150 nm. Thus, a ridge portion is formed as shown in FIG.
32
.
Then, the SiO
2
film
110
is formed on the overall surface by plasma CVD, and thereafter partially removed from the part of the n-type GaN contact layer
104
as shown in FIG.
33
. The n-side electrode
112
is formed on the part of the n-type GaN contact layer
104
from which the SiO
2
film
110
is partially removed.
Finally, the SiO
2
film
110
is partially removed from the upper surface of the p-side electrode
109
consisting of the Pd-based electrode, followed by formation of the pad electrodes
111
and
113
on the p-side electrode
109
and the n-side electrode
112
, as shown in FIG.
28
.
The nitride-based semiconductor laser element
150
shown in
FIG. 28
is fixed onto the submount (heat radiation base)
170
fixed to a stem
171
with a fusing material
160
such as solder, as shown in FIG.
34
. In this case, the surface (the back surface of the sapphire substrate
101
) of the element
150
opposite to the ridge portion is welded to the submount
170
in the junction-up system.
The conventional nitride-based semiconductor laser element
150
having the p-side electrode
109
consisting of the Pd-based electrode is formed in the aforementioned manner.
In the aforementioned conventional nitride-based semiconductor laser element
150
having the p-side electrode
109
consisting of the Pd-based electrode, however, the p-side electrode
109
consisting of the Pd-based electrode tends to peel during the fabrication process due to weak adhesion to the p-type GaN contact layer
108
. Therefore, it is disadvantageously difficult to improve reliability of the element
150
.
In the conventional nitride-based semiconductor laser element
150
having the p-side electrode
109
consisting of the Pd-based electrode, further, the contact property of the p-side electrode
109
is disadvantageously deteriorated due to heat or stress in a step of forming the pad electrode
112
on the p-side electrode
109
or an assembling step. In this case, contact resistance is so increased as to disadvantageously increase the operating voltage.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a highly reliable nitride-based semiconductor light-emitting device having low operating voltage.
Another object of the present invention is to increase adhesion of the whole of an electrode layer to a nitride-based semiconductor layer without damaging a low contact property in the aforementioned nitride-based semiconductor light-emitting device.
Still another object of the present inventio
Nomura Yasuhiko
Oota Kiyoshi
Yamaguchi Tsutomu
McDermott & Will & Emery
Pizarro-Crespo Marcos D.
Sanyo Electric Co,. Ltd.
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