Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2002-02-01
2004-02-24
Ip, Paul (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S043010, C372S044010, C372S045013
Reexamination Certificate
active
06697407
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-055109 filed Feb. 28, 2001, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates a semiconductor laser and a method of manufacturing the semiconductor laser. Particularly, the present invention relates to a semiconductor laser and a method of manufacturing the semiconductor laser which is capable of attaining a high power laser light emission with high efficiency by reducing a reactive current which does not contribute to laser oscillation.
2. Description of the Related Art
Recently, with the progress of optical communications systems, long-distance communications by means of optical communications cables has been realized.
The semiconductor laser to be employed as a light source of the optical communications systems must have characteristics of high efficiency and high power.
FIG. 5
shows a sectional structure of a generally used buried-type semiconductor laser capable of obtaining a high efficiency laser light. The semiconductor laser of this type is conventionally known and disclosed in Jpn. Pat. Appln. No. 7-22691.
Specifically as shown in
FIG. 5
, in the semiconductor laser, a first clad layer
2
of a p-type InP is formed on a p-type InP substrate
1
having a (
100
) crystal plane or a crystal plane close to the (
100
) crystal plane as the upper surface.
On the upper center of the first clad layer
2
, a mesa stripe portion
3
having a trapezoidal shape is formed.
Furthermore, outside the mesa stripe portion
3
on the first clad layer
2
, a current blocking portion
4
is formed.
The mesa stripe portion
3
is formed of a projecting portion
2
a
of the first clad layer
2
, an active layer
5
of non-doped InGaAsP formed on the projecting portion
2
a
of the first clad layer
2
, and a second clad layer
6
of n-type InP formed on the active layer
5
.
The current blocking portion
4
at both sides of the mesa stripe portion
3
is formed of an n-type current blocking layer
7
of n-type InP for blocking migration of holes present at the lower side, and a high resistance semiconductor layer
8
doped with Fe, for blocking migration of electrons present at the upper side.
A third clad layer
9
of n-type InP is formed so as to simultaneously cover the upper surface of the mesa stripe portion
3
and the upper surface of the current blocking portion
4
.
On the third clad layer
9
, a contact layer
10
is formed.
On the upper surface of the contact layer
10
, an insulating layer
11
is formed so as to face the current blocking portion
4
.
An electrode plate
12
is attached to the portion of the upper surface of the contact layer
10
facing to the mesa stripe portion
3
.
Furthermore, an electrode plate
13
is attached also on the lower surface of the P-type InP substrate
1
.
In the semiconductor laser thus constructed, when a direct-current driving voltage is applied across the upper and lower electrode plates
12
and
13
, the current is restricted by the current blocking portion
4
due to the presence of the n-type current blocking layer
7
and the high-resistance semiconductor layer
8
.
As a result, the current is concentrated on the mesa-stripe portion
3
at the center, increasing the efficiency of laser light emitting from the active layer
5
of the mesa stripe portion
3
.
Furthermore, in the semiconductor laser, it is necessary to minimize a reactive current (leakage current) flowing not through the active layer
5
of the mesa stripe portion
3
but from the second clad layer
6
to the n-type current blocking layer
7
.
To avoid direct contact between the first clad layer
2
(
2
a
) formed of p-type InP and the high-resistance semiconductor layer
8
, a top-end
7
a
of the n-type current blocking layer
7
is positioned on the border between the active layer
5
and the second clad layer
6
.
To form such a structure, etching is performed in its manufacturing process of the semiconductor laser in the conditions under which a (
111
)B crystal plane can be exposed on an inclined side surface
14
of the mesa stripe portion
3
having a trapezoidal shape.
Furthermore, a (
100
) crystal plane is exposed by etching on the upper surface
15
of the first clad layer
2
outside the mesa stripe portion
3
.
Thereafter, the n-type current blocking layer
7
is grown on the inclined side surface
14
of the mesa stripe portion
3
and on the upper surface
15
of the first clad layer
2
by use of a metal-organic-vapor-phase epitaxy (MOVPE) method.
As known well, the n-type current blocking layer
7
is grown directly on the (
100
) crystal plane but not grown directly on the (
111
)B crystal plane.
Accordingly, in the case where the n-type current blocking layer
7
is grown by use of the metal-organic-vapor-phase epitaxy (MOVPE) method, a tapered tip
7
a
of the n-type current blocking layer
7
creeps up along the inclined side surface
14
of the mesa stripe portion
3
in accordance with the growth of the n-type current blocking layer
7
, as shown in FIG.
6
.
Accordingly, when the tapered tip
7
a
of the n-type current blocking layer
7
reaches the border between the active layer
5
and the second clad layer
6
, the growth operation of the n-type current blocking layer
7
by use of the metal-organic-vapor-phase epitaxy (MOVPE) method is terminated The manufacturing method mentioned above makes it possible to minimize the reactive current (leakage current) flowing from the second clad layer
6
to the n-type current blocking layer
7
without passing through the active layer
5
of the mesa stripe portion
3
.
Furthermore, by employing the Fe-doped high resistant semiconductor layer
8
as the current blocking portion
4
, a high-speed operation can be attained.
However, the conventional semiconductor laser having the structure shown in
FIG. 5
still have the following problems to be solved.
In the case where the n-type current blocking layer
7
is grown by the metal-organic-vapor-phase epitaxy (MOVPE) method as shown in
FIG. 6
, the tapered tip
7
a
of the n-type current blocking layer
7
creeps up along the inclined side surface
14
of the mesa stripe portion
3
as it grows.
Thereafter, when the tapered tip
7
a
reaches the border between the active layer
5
and the second clad layer
6
, it is necessary to terminate the growth operation using the metal-organic-vapor-phase epitaxy (MOVPE) method.
However, the timing (time) at which the tapered tip
7
a
reaches the border between the active layer
5
and the second clad layer
6
varies depending upon voltage application conditions of the metal-organic-vapor-phase epitaxy (MOVPE) method and the height of the trapezoidal mesa stripe portion
3
which slightly varies depending upon etching conditions.
Therefore, the tapered tip
7
a
of the n-type current blocking layer
7
fails to reach the border between the active layer
5
and the second clad layer
6
in some cases, and in other cases, it reaches up to the middle of the side surface of the second clad layer
6
.
As a result, the first clad layer
2
(
2
a
) of p-type InP may be brought into direct contact with the high resistance semiconductor layer
8
. Alternatively, the amount of the reactive current (leakage current) flowing from the second clad layer
6
to the n-type current blocking layer
7
may increase, with the result that stable and high efficient laser-emitting characteristics as the semiconductor laser cannot be obtained.
Furthermore, in the conventional semiconductor laser mentioned above, a p-type InP substrate is employed.
The p-type InP substrate, as is known well, has a high specific resistance compared to an n-type InP substrate.
As a result, if the amount of a current to be supplied to the semiconductor laser is increased in order to obtain a high-power laser, the generation of heat increases.
Therefore, the semiconductor laser employing the p-type In
Kikugawa Tomoyuki
Nagashima Yasuaki
Shinone Katsunori
Al Nazer Leith A
Anritsu Corporation
Frishauf Holtz Goodman & Chick P.C.
LandOfFree
Semiconductor laser attaining high efficiency and high... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Semiconductor laser attaining high efficiency and high..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor laser attaining high efficiency and high... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3294688