Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With particular semiconductor material
Reexamination Certificate
2003-03-24
2004-09-14
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With particular semiconductor material
C257S103000, C257S765000
Reexamination Certificate
active
06791120
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a nitride-based semiconductor device and a method of fabricating the same, and more particularly, it relates to a nitride-based semiconductor device having an electrode and a method of fabricating the same.
2. Description of the Background Art
A nitride-based semiconductor laser device has recently been expected as a light source for an advanced large capacity optical disk, and actively developed.
In general, an insulating sapphire substrate is employed for forming a nitride-based semiconductor laser device. When a nitride-based semiconductor layer is formed on the sapphire substrate, however, a large number of defects (dislocations) are disadvantageously formed in the nitride-based semiconductor layer due to large difference between the lattice constants of the sapphire substrate and the nitride-based semiconductor layer. Consequently, the characteristics of the nitride-based semiconductor laser device are disadvantageously reduced.
In this regard, a nitride-based semiconductor laser device employing a nitride-based semiconductor substrate such as a GaN substrate having small difference in lattice constant with respect to a nitride-based semiconductor layer is proposed in general.
FIG. 7
is a sectional view showing a conventional nitride-based semiconductor laser device employing an n-type GaN substrate
101
. Referring to
FIG. 7
, nitride-based semiconductor layers (
102
to
110
) are grown on a Ga face ((HKLM) plane: M denotes a positive integer) to be improved in crystallinity in a process of fabricating the conventional nitride-based semiconductor laser device. A nitrogen face ((HKL-M) plane: M denotes a positive integer) of the n-type GaN substrate
101
having a wurtzite structure is employed as the back surface, so that an n-side electrode
112
is formed on this back surface of the n-type GaN substrate
101
. The fabrication process for the conventional nitride-based semiconductor laser device is now described in detail.
As shown in
FIG. 7
, an n-type layer
102
consisting of n-type GaN having a thickness of about 3 &mgr;m, an n-type buffer layer
103
consisting of n-type In
0.05
Ga
0.95
N having a thickness of about 100 nm, an n-type cladding layer
104
consisting of n-type Al
0.05
Ga
0.95
N having a thickness of about 400 nm, an n-type light guide layer
105
consisting of n-type GaN having a thickness of about 70 nm, an MQW (multiple quantum well) active layer
106
having an MQW structure, a p-type layer
107
consisting of p-type Al
0.2
Ga
0.8
N having a thickness of about 200 nm, a p-type light guide layer
108
consisting of p-type GaN having a thickness of about 70 nm, a p-type cladding layer
109
consisting of p-type Al
0.05
Ga
0.95
N having a thickness of about 400 nm and a p-type contact layer
110
consisting of p-type GaN having a thickness of about 100 nm are successively formed on the upper surface (Ga face) of the n-type GaN substrate
101
having a thickness of about 300 &mgr;m to about 500 &mgr;m.
Then, a p-side electrode
111
is formed on a prescribed region of the upper surface of the p-type contact layer
110
. The back surface of the n-type GaN substrate
101
is polished until the thickness of the n-type GaN substrate
101
reaches a prescribed level of about 100 &mgr;m, and an n-side electrode
112
is thereafter formed on the back surface (nitrogen face) of the n-type GaN substrate
101
. Finally, the n-type GaN substrate
101
and the layers
102
to
110
are cleft thereby performing element isolation and forming a cavity facet. Thus, the conventional nitride-based semiconductor laser device shown in
FIG. 7
is completed.
In the conventional nitride-based semiconductor laser device shown in
FIG. 7
, however, the n-type GaN substrate
101
is so hard that it is difficult to excellently perform device isolation and form the cavity facet by cleavage. In order to cope with such inconvenience, a method of mechanically polishing the back surface of the n-type GaN substrate
101
before the cleavage step for reducing irregularity on the back surface thereby excellently performing element isolation and forming the cavity facet is proposed. This method is disclosed in Japanese Patent Laying-Open No. 2002-26438, for example.
In the aforementioned conventional method disclosed in Japanese Patent Laying-Open No. 2002-26438, however, stress is applied in the vicinity of the back surface of the n-type GaN substrate
101
when the back surface of the n-type GaN substrate
101
is mechanically polished. Therefore, microscopic defects such as cracks are disadvantageously formed in the vicinity of the back surface of the n-type GaN substrate
101
. Consequently, contact resistance between the n-type GaN substrate
101
and the n-side electrode
112
formed on the back surface (nitrogen face) thereof is disadvantageously increased.
Further, the nitrogen face of the n-type GaN substrate
101
is so easily oxidized that the contact resistance between the n-type GaN substrate
101
and the n-side electrode
112
formed on the back surface (nitrogen face) thereof is disadvantageously increased also by this.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of fabricating a nitride-based semiconductor device capable of reducing contact resistance between the back surface of a nitride-based semiconductor substrate or the like and an electrode.
Another object of the present invention is to reduce the number of defects in the vicinity of the back surface of the nitride-based semiconductor substrate or the like in the aforementioned method of fabricating a nitride-based semiconductor device.
Still another object of the present invention is to provide a nitride-based semiconductor device capable of reducing contact resistance between the back surface of a nitride-based semiconductor substrate or the like and an electrode.
In order to attain the aforementioned objects, a method of fabricating a nitride-based semiconductor device according to a first aspect of the present invention comprises steps of etching the back surface of a first semiconductor layer consisting of either an n-type nitride-based semiconductor layer or a nitride-based semiconductor substrate having a wurtzite structure and thereafter forming an n-side electrode on the etched back surface of the first semiconductor layer.
In the method of fabricating a nitride-based semiconductor device according to the first aspect, the back surface of the first semiconductor layer consisting of either an n-type nitride-based semiconductor layer or a nitride-based semiconductor substrate having a wurtzite structure is etched as hereinabove described, whereby a region including defects in the vicinity of the back surface of the first semiconductor layer resulting from a polishing step or the like can be removed for reducing the number of defects in the vicinity of the back surface of the first semiconductor layer. Thus, an electron carrier concentration can be inhibited from reduction resulting from trap of electron carriers by defects, so that the electron carrier concentration can be increased on the back surface of the first semiconductor layer. Consequently, contact resistance between the first semiconductor layer and the n-side electrode can be reduced. Further, the back surface of the first semiconductor layer is so etched that flatness thereof can be improved as compared with that of a mechanically polished back surface. Thus, the n-side electrode formed on the back surface of the first semiconductor layer can also be improved in flatness, whereby adhesion between the n-side electrode and a radiator base can be improved when the former is mounted on the latter. Consequently, excellent radiability can be attained. Further, the n-side electrode formed on the back surface of the first semiconductor layer can be so improved in flatness that wire bondability with respect to the n-side electrode can be improved when the n-side electrode is wire-bonded.
In the aforementioned method of fabri
Hata Masayuki
Nomura Yasuhiko
Toda Tadao
Yamaguchi Tsutomu
McDermott Will & Emery LLP
Nelms David
Nguyen Thinh T
Sanyo Electric Co,. Ltd.
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