Semiconductor device manufacturing: process – Introduction of conductivity modifying dopant into... – Ion implantation of dopant into semiconductor region
Reexamination Certificate
2002-01-30
2004-06-01
Lebentritt, Michael S. (Department: 2824)
Semiconductor device manufacturing: process
Introduction of conductivity modifying dopant into...
Ion implantation of dopant into semiconductor region
C438S505000, C438S508000, C438S522000, C438S604000
Reexamination Certificate
active
06743702
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a nitride-based semiconductor laser device and a method of forming the same, and more particularly, it relates to a nitride-based semiconductor laser device including an electrode layer and a method of forming the same.
2. Description of the Prior Art
A nitride-based semiconductor laser device is recently expected for application to a light source for a future large capacity optical disk, and actively developed. In order to reduce the operating voltage of the nitride-based semiconductor laser device and improve the reliability thereof, the contact resistance of an electrode must inevitably be reduced. In particular, a nitride-based semiconductor has low p-type carrier concentration, and hence it is difficult to attain an excellent ohmic property (low contact resistance) in relation to a p-side electrode. Therefore, a Pd-based electrode material such as a Pd/Au electrode or a Pd/Pt/Au electrode containing Pd having an excellent ohmic property is recently employed as the p-side electrode.
FIG. 35
is a sectional view showing a first conventional nitride-based semiconductor laser device having a Pd-based electrode. The structure of the first conventional nitride-based semiconductor laser device is now described with reference to FIG.
35
. In the first conventional nitride-based semiconductor laser device, an AlGaN low-temperature buffer layer
202
of about 15 nm in thickness is formed on a sapphire substrate
201
. An undoped GaN layer
203
of about 3 &mgr;m in thickness is formed on the AlGaN low-temperature buffer layer
202
. An n-type GaN contact layer
204
is formed on the undoped GaN layer
203
in a thickness of about 5 &mgr;m. An n-type AlGaN cladding layer
205
of about 1 &mgr;m in thickness, an MQW (multiple quantum well) active layer
206
, consisting of InGaN, of about 50 nm in thickness and a p-type AlGaN cladding layer
207
of about 300 nm in thickness having a convex portion are formed on the n-type GaN contact layer
204
. A p-type GaN contact layer
208
of about 70 nm in thickness is formed on the convex portion of the p-type AlGaN cladding layer
207
.
A p-side electrode
209
consisting of a Pd-based electrode having a three-layer structure formed by stacking 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
208
. An SiO
2
film
210
is formed to cover the upper surface of the p-side electrode
209
and regions excluding part of the upper surface of the n-type GaN contact layer
204
. A pad electrode
211
is formed to cover the SiO
2
film
210
and come into contact with the upper surface of the p-side electrode
209
.
The layers from the p-type AlGaN cladding layer
207
to the n-type GaN contact layer
204
are partially removed. An n-side electrode
212
is formed to come into contact with the exposed upper surface of the n-type GaN contact layer
204
. A pad electrode
213
is formed to come into contact with the n-side electrode
212
.
FIGS. 36
to
40
are sectional views for illustrating a process of fabricating the first conventional nitride-based semiconductor laser device having the Pd-based electrode shown in FIG.
35
.
FIG. 41
is a sectional view showing the first conventional nitride-based semiconductor laser device shown in
FIG. 35
mounted on a submount in a junction-up system from the substrate side. The term “junction-up system” stands for a system of mounting a nitride-based semiconductor laser device on a submount so that the distance between a substrate and the submount is smaller than that between an active layer and the submount. The fabrication process for the first conventional nitride-based semiconductor laser device having the Pd-based electrode is now described with reference to
FIGS. 35
to
41
.
First, the AlGaN low-temperature buffer layer
202
is grown on the sapphire substrate
201
by MOCVD (metal organic chemical vapor deposition) under a low-temperature condition of about 600° C. in a thickness of about 15 nm, in order to relax lattice mismatching. The undoped GaN layer
203
is formed on the AlGaN low-temperature buffer layer
202
by MOCVD in a thickness of about 3 &mgr;m.
Thereafter the n-type GaN contact layer
204
of about 5 &mgr;m in thickness, the n-type AlGaN cladding layer
205
of about 1 &mgr;m in thickness, the MQW active layer
206
, consisting of InGaN, of about 50 nm in thickness, the p-type AlGaN cladding layer
207
of about 300 nm in thickness and the p-type GaN contact layer
208
of about 70 nm in thickness are successively formed on the undoped GaN layer
203
by MOCVD.
Then, the layers from the p-type GaN contact layer
208
to the n-type GaN contact layer
204
are partially removed by anisotropic dry etching, as shown in FIG.
37
.
Then, a multilayer film 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 stacked in ascending order is formed 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
209
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.
38
. Thereafter the uppermost Ni layer forming the p-side electrode
209
is employed as an etching mask for etching the p-type GaN contact layer
208
while etching the p-type AlGaN cladding layer
207
by about 150 nm by anisotropic dry etching with CF
4
gas. Thus, a ridge portion shown in
FIG. 39
is formed.
Then, the SiO
2
film
210
is formed on the overall surface by plasma CVD and partially removed from a portion of the n-type GaN contact layer
204
, as shown in FIG.
40
. The n-side electrode
212
is formed on the portion of the n-type GaN contact layer
204
from which the SiO
2
film
210
is removed.
Then, part of the SiO
2
film
210
located on the upper surface of the p-side electrode
209
consisting of the Pd-based electrode is removed, followed by formation of the pad electrodes
211
and
213
on the p-side electrode
209
and the n-side electrode
212
respectively, as shown in FIG.
35
.
The nitride-based semiconductor laser device shown in
FIG. 35
is fixed onto a submount (radiation base)
270
fixed to a stem
271
with a fusible material
260
such as solder, as shown in FIG.
41
. In this case, the surface (the back surface of the sapphire substrate
201
) of the device opposed to the ridge portion is fused to the submount
270
in the junction-up system.
The first conventional nitride-based semiconductor laser device having the p-side electrode
209
consisting of the Pd-based electrode is formed in the aforementioned manner.
In the aforementioned first conventional nitride-based semiconductor laser device having the p-side electrode
209
consisting of the Pd-based electrode, however, the adhesive force of the p-side electrode
209
consisting of the Pd-based electrode to the p-type GaN contact layer
208
is so weak that the p-side electrode
209
consisting of the Pd-based electrode disadvantageously readily peels off in an intermediate stage of the fabrication process. Therefore, it is difficult to improve the reliability of the device.
In the first conventional nitride-based semiconductor laser device having the p-side electrode
209
consisting of the Pd-based electrode, further, heat or stress disadvantageously deteriorates the contact characteristic of the p-side electrode
209
in the step of forming the pad electrode
211
on the p-side electrode
209
or in an assembling step. In this case, contact resistance is increased to disadvantageously increase the operating voltage.
FIG. 42
is a sectional view showing the structure of a second conventional nitride-based semiconductor laser device
350
. Referring to
FIG. 42
, an n-type GaN contact layer
302
of about 5 &mgr;m in thickness is formed on a sapphire substrate
301
in the second conventional nitride
Goto Takenori
Nomura Yasuhiko
Oota Kiyoshi
Yamaguchi Tsutomu
Lebentritt Michael S.
McDermott & Will & Emery
Sanyo Electric Co,. Ltd.
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