Method for fabricating nitride semiconductor device

Details Method for fabricating nitride semiconductor device Method for fabricating nitride semiconductor device

2001-03-16

2003-02-11

Picardat, Kevin M. (Department: 2822)

Semiconductor device manufacturing: process

Making device or circuit emissive of nonelectrical signal

Compound semiconductor

C438S507000, C438S508000

Reexamination Certificate

active

06518082

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a method for fabricating a semiconductor device such as a short wavelength light-emitting device, particularly a GaN-based semiconductor laser device, or the like, which is expected to be used in the field of optical information processing, etc.
BACKGROUND ART
Among the group III-V compound semiconductors, nitride semiconductors containing nitrogen (N) as the group V element are seen to be promising materials of a short wavelength light-emitting device for their relatively large band gap. Among others, so-called nitride semiconductors made of a gallium nitride-based compound semiconductor, e.g., a GaN-based semiconductor of Al
x
Ga
y
In
z
N (where 0≦x, y, z≦1, x+y+z=1), have been actively researched, and blue or green light-emitting diode devices (LEDs) have been put into practical use. In order to increase the capacity of an optical disk apparatus, there is a strong demand for a semiconductor laser device having a 400 nm band oscillation wavelength. To this end, a semiconductor laser device using a GaN-based semiconductor has been attracting public attention, and the current state of the art of such a semiconductor laser device is close to a practical level.
A conventional GaN-based semiconductor laser device will now be described with reference to the accompanying drawings.
FIG. 7
is a cross-sectional view illustrating a conventional GaN-based semiconductor laser device which has been confirmed to produce laser oscillation. As illustrated in
FIG. 7
, a buffer layer
102
made of GaN for reducing the lattice mismatch between a substrate
101
and a GaN-based semiconductor grown on the substrate
101
, an n-type contact layer
103
made of n-type GaN which includes a device formation region and an n-side electrode formation region, a first cladding layer
104
made of n-type Al
0.07
Ga
0.93
N which is formed in the device formation region of the n-type contact layer
103
, a first optical guide layer
105
made of n-type GaN, a multiple quantum well active layer
106
made of a stack of Ga
1−x
In
x
N/Ga
1−y
In
y
N (0<y<x<1), a second optical guide layer
107
made of p-type GaN, a second cladding layer
108
made of p-type Al
0.07
Ga
0.93
N, and a p-type contact layer
109
made of p-type GaN, are formed in this order on the substrate
101
made of sapphire by using a metal-organic vapor phase epitaxy (MOVPE) method.
A ridge stripe portion
108
a
whose width is about 3 &mgr;m to about 10 &mgr;m is formed on the second cladding layer
108
, and the p-type contact layer
109
is formed on the ridge stripe portion
108
a
. The side region of the p-type contact layer
109
and the ridge stripe portion
108
a
of the second cladding layer
108
and the side surfaces of the epitaxial layers are covered with an insulation film
110
.
A p-side electrode
111
made of a stack of Ni/Au, for example, is formed on the insulation film
110
including the p-type contact layer
109
so as to be in contact with the p-type contact layer
109
, and an n-side electrode
112
made of a stack of Ti/Al, for example, is formed in the n-side electrode formation region of the n-type contact layer
103
.
In a semiconductor laser device having such a structure, when the n-side electrode
112
is grounded and a voltage is applied to the p-side electrode
111
, holes and electrons are injected into the multiple quantum well active layer
106
from the p-side electrode
111
side and from the n-side electrode
112
side, respectively. The injected holes and electrons produce an optical gain in the multiple quantum well active layer
106
, thereby causing laser oscillation with an oscillation wavelength of about 400 nm. Note, however, that the oscillation wavelength varies depending upon the composition or thickness of the stack of Ga
1−x
In
x
N/Ga
1−y
In
y
N forming the multiple quantum well active layer
106
. At present, there has been realized a semiconductor laser device of this structure capable of continuous-wave oscillation at room temperature or higher.
It is disclosed that in order to grow a GaN-based semiconductor containing In, i.e., a semiconductor made of GaInN, by using an MOVPE method, it is preferred to set the crystal growth temperature to about 800° C. and to use a nitrogen (N
2
) gas as a carrier gas (Applied Physics Letters, vol. 59, p. 2251, 1991). On the other hand, for a semiconductor layer containing no In such as the cladding layer
104
,
108
made of Al
0.07
Ga
0.93
N, the optical guide layer
105
,
107
made of GaN, or the like, it is typical that the growth temperature is as high as 1000° C. or higher and a hydrogen (H
2
) gas is used as the carrier gas. The series of growth processes are described in detail in, for example, Japanese Laid-Open Patent Publication No. 6-196757 or Japanese Laid-Open Patent Publication No. 6-177423.
The outline of the processes will be described below.
First, the substrate
101
is held in a reaction chamber, and a heat treatment is performed by increasing the substrate temperature to 1050° C. while introducing an H
2
gas. Next, after the substrate temperature is decreased to 510° C., ammonia (NH
3
) and trimethylgallium (TMG), which are reaction gases, are introduced onto the substrate
101
, thereby growing the buffer layer
102
made of GaN.
Then, the introduction of TMG is stopped and the substrate temperature is increased to 1030° C., and TMG and monosilane (SiH
4
) are introduced, with an H
2
gas as a carrier gas, thereby growing the n-type contact layer
103
made of n-type GaN, after which trimethylaluminum (TMA) is added as a group III material gas containing Al, thereby successively growing the first cladding layer
104
made of n-type Al
0.07
Ga
0.93
N.
Then, the supply of the material gasses is stopped, and the substrate temperature is decreased to 800° C. Then, the carrier gas is switched from an H
2
gas to an N
2
gas, and TMG and trimethylindium (TMI) are introduced as group III material gases, thereby forming the multiple quantum well active layer
106
made of a stack of Ga
1−x
In
x
N/Ga
1−y
In
y
N.
Then, the supply of the group III material gas is stopped, and the substrate temperature is increased again to 1020° C., while the carrier gas is switched back from an N
2
gas to an H
2
gas, and TMG, TMA and cyclopentadienylmagnesium (Cp
2
Mg), or the like, as a p-type dopant are introduced, thereby successively growing the second optical guide layer
107
made of p-type GaN, the second cladding layer
108
made of p-type Al
0.07
Ga
0.93
N and the p-type contact layer
109
made of p-type GaN.
In the heating step after the formation of the active layer, a protection layer made of GaN (Japanese Laid-Open Patent Publication No. 9-186363) or a protection layer made of Al
0.2
Ga
0.8
N (e.g., Japanese Journal of Applied physics, Vol. 35, p. L74, 1996) may be formed in order to prevent re-evaporation of In from the multiple quantum well active layer
106
.
However, in the conventional GaN-based semiconductor laser device as described above, a deterioration in the quality of the n-type contact layer
103
made of n-type GaN or the first cladding layer
104
made of n-type Al
0.07
Ga
0.93
N (note that the Al content is 0.1 in Japanese Laid-Open Patent Publication No. 6-196757 or Japanese Laid-Open Patent Publication No. 6-177423) to be the underlying layer for growing the multiple quantum well active layer
106
thereon causes a deterioration in the crystal quality of the multiple quantum well active layer
106
to be grown thereon, thereby leading to problems such as a deterioration in the light-emitting efficiency or an increase in the threshold current in the light-emitting diode device or the semiconductor laser device.
The present invention has been made in view of the above-described problems in the prior art, and has an object to improve the crystal quality of an active region or a peripheral region of the active region so as to realize a nitride semiconductor device having desirable operating characteristics.
DI

Affiliated with

Also associated with

Rating

Method for fabricating nitride semiconductor device does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method for fabricating nitride semiconductor device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for fabricating nitride semiconductor device will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3139504