Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2000-10-19
2003-02-11
Ghyka, Alexander (Department: 2812)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S044000, C438S046000, C438S607000
Reexamination Certificate
active
06518159
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor laser device made of AlGaInP or its analogues and a method for fabricating the same. In particular the present invention relates to a semiconductor laser device made by utilizing MBE process which may grow an AlGaInP-based layer at a lower temperature to provide an improved crystal quality, a lower threshold in oscillation and a high efficiency in light emission and a method for fabricating the same.
AlGaInP-based semiconductor laser devices are used as optical sources for optical disc systems, laser printers, bar-code readers and the like, accordingly researches and developments for such devices have been enthusiastically carried out. There are some prior patents relating to AlGaInP semiconductor laser devices and a method for fabricating the same, such as Japanese Laid-Open Patent Publication No. 8-228041, Japanese Laid-Open Patent Publication No. 8-228047, Japanese Laid-Open Patent Publication No. 6-296062, Japanese Laid-Open Patent Publication No. 2-168690, Japanese Laid-Open Patent Publication No. 8-181385, Japanese Laid-Open Patent Publication No. 5-67839, Japanese Laid-Open Patent Publication No.7-50453, Japanese Laid-Open Patent Publication No. 7-50452, Japanese Laid-Open Patent Publication No. 7-22696 and Japanese Laid-Open Patent Publication No. 6-275915.
In the above patents, MOCVD process has been mainly used for growing AlGaInP crystal layers which are utilized to construct AlGaInP-based semiconductor laser devices, since the MOCVD process has provided better crystal qualities than MBE process which is one of major crystal growth processes. While the MBE process provides a higher carrier density in p-type semiconductor layers where the carrier density is important to improve electric characteristics in semiconductor laser devices and utilizes Be of a lower diffusion as an impurity to achieve such carrier density so as to realize a semiconductor laser devise of long-term reliability. There are two major advantages of the MBE process. For these reasons, an improvement in crystal qualities for crystals grown by the MBE process is effective to obtain an improved characteristic of AlGaInP-based semiconductor laser devices.
Now, AlGaInP-based semiconductor laser devices by MBE (molecular beam epitaxy) process will be described hereinafter.
FIGS. 1
to
4
are respectively a part of a flow chart illustrating a conventional process for fabricating AlGaInP semiconductor laser devices.
FIGS. 5
to
7
also are respectively a part of a flow chart continuing from
FIGS. 1
to
4
for illustrating the conventional process.
As shown in
FIG. 1
, an n-type (Al
0.72
Ga
0.28
)
0.51
In
0.49
cladding layer
22
, a Ga
0.51
In
0.49
P active layer
23
, a first p-type (Al
0.72
Ga
0.28
)
0.51
In
0.49
P cladding layer
24
, a non-dope Ga
0.62
In
0.38
P etch-stop layer
25
, a second p-type (Al
0.72
Ga
0.28
)
0.51
In
0.49
P cladding layer
26
, a p-type Ga
0.51
In
0.49
P intermediate layer
27
and a p-type GaAs cap layer
28
are successively grown by the MBE process at a temperature of 450° C. on amain facet of an n-type GaAs substrate
21
which has a facet-direction (100) just aligned in place. Then an Al
2
O
3
layer
29
is deposited on the cap layer
28
.
Then, a resist layer
30
is applied onto the Al
2
O
3
layer
29
for photoetching to obtain stripe-shaped Al
2
O
3
layer
29
by a pattern process. As shown in
FIG. 2
, an etching process follows using the Al
2
O
3
layer
29
as a mask to partially remove the cap layer
28
, the p-type Ga
0.51
In
0.49
intermediate layer
27
and the second p-type (Al
0.72
Ga
0.28
)
0.51
In
0.49
P cladding layer
26
so as to form a ridge beneath the Al
2
O
3
layer. Then, as shown in
FIG. 3
, after removing the resist layer
30
, a second MBE process is carried out to form an n-type GaAs current blocking layer
31
at the both sides of the ridge.
During the second MBE process, a GaAs crystal
32
of a polycrystalline is grown on the surface of the Al
2
O
3
layer
29
. The a resist layer
33
is applied by a spinner wherein the resist layer
33
is not substantially applied on the polycrystalline GaAs crystal
32
but on the current blocking layer
31
. Subsequently, the resist
33
on the whole surface is ashed by O
3
-UV to have the resist
33
coated only on the n-type GaAs current blocking layer
31
as shown in FIG.
4
.
Then, as shown in
FIG. 5
, the polycrystalline GaAs crystal
32
is removed by etching by using the resist
33
as a mask. Subsequently, the resist
33
is removed and the Al
2
O
3
layer
29
is also removed by etching as shown in FIG.
6
. Next, a third MBE process is carried out to form a contact layer
34
. Finally electrodes
35
and
36
are formed respectively on the top of the array obtained as described above and on the back of the n-type GaAs substrate
21
to obtain an AlGaInP-based semiconductor red-laser device as shown in FIG.
7
.
Since MBE process supplies metal material in molecules, it allows the metal to grow at a lower temperature comparing with an MOCVD (Metal Organic Chemical Vapor Deposition which is also a type of chemical vapor deposition) where a material is supplied in an organic metal. Further, the MOCVD process allows the metal to grow only at a temperature ranging from 600° C. to 700° C. which is higher than the decomposition temperature of the organic metal. In other words, the growth temperature must be higher than 520° C. which is the evaporating temperature of In atoms, whereby the thickness of the grown crystal becomes smaller comparing with the supplied In. That is to say, the crystal is grown during re-evaporation of itself. Once re-evaporation of the crystal happens, its compound crystal rate is varied not only by material supply but also by its growth temperature, thereby making it difficult to control characteristics of a semiconductor laser device, such as oscillating wave-length.
However, even by using MBE process it is still preferable to grow a crystal at a higher temperature in order to improve crystal qualities. If an AlGaInP-based material is grown at a temperature lower than 400°C., for example, a specific resistance of the crystal is too large to fabricate a semiconductor laser device because metal molecules of the material do not seem to locate in place, resulting in a poor crystal quality.
While, a substrate having an aligned facet-direction of (100) obtained by MBE growth process at a higher than 480° C. gives a wide spectrum of photoluminescence (referred to as PL hereinafter) which is unfavorable for a crystal applied to a semiconductor laser device.
Further, an AlGaInP-based semiconductor layer grown in the conventional manner tends to be affected by impurities on a GaAs substrate surface, resulting in a poor morphology, causing a crystal defect and the like.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a semiconductor laser device having a lower oscillation threshold and a high light-emission efficiency by growing AlGaInP-based semiconductor layers on a GaAs substrate having a facet, which is to be a main facet, inclined by &thgr;° in [011] direction from (100) facet, that is to say, by growing AlGaInP semiconductor layers of a good crystal quality.
Another object of the present invention is to provide a semiconductor fabricating method which permits growing at a lower temperature than the re-evaporation temperature of In, thus improving the crystal quality of AlGaInP-based semiconductor device by MBE growth process allowing a small deviation in compound crystal ratios to give a stable characteristic and which has less influence by impurities on a GaAs substrate surface, thereby giving a good morphology when growing an AlGaInP-based semiconductor layer to lessen crystal defects.
Still another object of the present invention is to provide a semiconductor laser device having a cladding layer of bandgap E
gc
made of III-V group compound semiconductor layer and an active layer of bandgap E
ga
which are stacked on a substrate having a facet, which
Ghyka Alexander
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
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