Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2001-08-14
2003-11-11
Leung, Quyen (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S045013, C438S022000
Reexamination Certificate
active
06647044
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor light-emitting device and a method of forming the same, and more particularly to a semiconductor laser device with a stripe-shaped mesa structure including a current injection center region and current non-injection side regions adjacent to facets and a method of forming the same.
2. Description of the Related Art
There has been known a semiconductor laser device with a stripe-shaped mesa structure including a current injection center region and current non-injection side regions adjacent to facets, wherein the current non-injection side regions are provided in order to avoid optical damages at the facets. The semiconductor device of this type will hereinafter be referred to as a facet non-injection type semiconductor laser.
FIG. 1
is a fragmentary schematic perspective view with a partially recessed view illustrative of a typical conventional internal structure of a facet non-injection type semiconductor laser. The semiconductor laser has an optical cavity which has a stripe-shaped ridge waveguide structure. The semiconductor laser is provided over an n-type semiconductor substrate
1
.
An n-type cladding layer
2
overlies the n-type semiconductor substrate
1
. An n-type etching stopper layer
3
overlies the n-type cladding layer
2
. An n-type inner cladding layer
4
overlies the n-type etching stopper layer
3
. An SCH-structure
5
including an active layer is provided over the n-type inner cladding layer
4
. A p-type inner cladding layer
6
overlies the SCH-structure
5
. A p-type etching stopper layer
7
overlies the p-type inner cladding layer
6
. A stripe-shaped ridge optical waveguide of a p-type cladding; layer
8
is selectively provided on a stripe-shaped selected region of an upper surface of the p-type etching stopper layer
7
. The stripe-shaped ridge optical waveguide extends in a longitudinal direction of the semiconductor laser.
A p-type cap layer
9
is selectively provided on a selected center region, except on both side regions adjacent to both facets, of the stripe-shaped ridge optical waveguide of the p-type cladding layer
8
. A first current blocking layer
10
of n-type is provided over the both side regions of the stripe-shaped ridge optical waveguide, and over the p-type etching stopper layer
7
as well as in contact with side walls of the stripe-shaped ridge optical waveguide of the p-type cladding layer
8
. The first current blocking layer
10
extends except over the p-type cap layer
9
selectively provided on the upper surface of the selected center region of the stripe-shaped ridge optical waveguide. A second current blocking layer
11
of n-type overlies the first current blocking layer
10
.
A p-type contact layer
12
overlies the second current blocking layer
11
and the p-type cap layer
9
. An n-electrode
13
is provided in contact width a bottom surface of the n-type semiconductor substrate
1
. A p-electrode
14
is provided in contact with a top surface of the p-type contact layer
12
. A current or carrier is injected through the p-type cap layer
9
and the selected center region of the stripe-shaped ridge optical waveguide
8
into the active layer of the SCH-structure
5
. The first and second current blocking layers
10
and
11
prevent current injections directly into the both side regions of the stripe-shaped ridge optical waveguide
8
adjacent to the bot facets.
The selected center region of the stripe-shaped ridge optical waveguide
8
may be regarded as a current injection region. The side regions of the stripe-shaped ridge optical waveguide
8
covered by the first and second current blocking layers
10
and
11
may be regarded as current non-injection regions. The current is directly injected through the p-type cap layer
9
into the current injection region, and the injected current is then diffused into the current non-injection regions underlying laminations of the first and second current blocking layers
10
and
11
.
Parts of the diffusion currents in in-plane directions through the current non-injection regions are supplied to the both facets. Namely, parts of the diffusion currents in parallel to the longitudinal direction reach the opposite facets. The stripe-shaped ridge optical waveguide
8
has a sheet resistance to currents in parallel to the longitudinal direction toward the opposite facets, wherein the longitudinal direction is parallel to a traveling direction of the stripe-shaped ridge optical waveguide
8
. As this sheet resistance is high, then a density of the injection current to the facet is low. As the density of the injection current to the facet is low, then a Joule heat generated per a unit time is low. The generated heat is low, then a temperature increase at the facets is low. This contributes to delay a deterioration of the facets due to optical damages upon a high output operation.
Meanwhile, it has also been known that in order to obtain a high output of the semiconductor laser, the ridged waveguide is designed to increase, the thickness for obtaining a large spot size. In order to avoid the increase in resistance of the device upon the increase in thickness of the ridged waveguide, the ridged waveguide is also designed to increase a doping concentration for reducing a resistivity of the ridged waveguide. The increase in doping concentration of the ridged waveguide decreases a sheet resistance of the current non-injection regions of the ridged waveguide. The decreased sheet resistance of the current non-injection regions increases the density of the current through the to the current non-injection regions toward the facets, whereby the Joule heat generated per a unit time is increased and the temperature increase at the facets is high. This promotes the deterioration of the facets due to optical damages upon a high output operation.
It has also been proposed to counter-measure this problem, wherein the current non-injection regions are decreased in height, whilst the current injection region is increased in height.
FIG. 2
is a fragmentary schematic perspective view with a partially recessed view illustrative of a conventionally modified internal structure of the facet non-injection type semiconductor laser. A structural difference of the semiconductor laser shown in
FIG. 2
from that shown in
FIG. 1
is only in that the ridged waveguide
8
is modified height, so that the current injection region is larger in height or thickness than the current non-injection regions.
The modified ridged waveguide
8
of
FIG. 2
may be formed by selective etching to the cladding layer only on the current non-injection regions prior to shaping the ridged waveguide.
FIGS. 3A through 3E
are fragmentary schematic views of semiconductor laser devices in sequential steps involved in the conventional fabrication method for the semiconductor laser device of FIG.
2
.
With reference to
FIG. 3A
, an n-type cladding layer
2
is formed over the n-type semiconductor substrate
1
. An n-type etching stopper layer
3
is formed over the n-type cladding layer
2
, An n-type inner cladding layer
4
is formed over the n-typo etching stopper layer
3
. An SCH-layer
5
including an active layer is formed over the n-type inner cladding layer
4
, A p-type inner cladding layer
6
is formed over the SCH-layer
5
. A p-type etching stopper layer
7
is formed over the p-type inner cladding layer
6
. A p-type cladding layer
8
is formed over the p-type etching stopper layer
7
. A p-type cap layer
9
is formed over the p-type cladding layer
8
.
A silicon dioxide film
15
is selectively formed on a selected center region of an upper surface of the p-type cap layer
9
except on both side regions separated from each other by the selected center region in the longitudinal direction. The silicon dioxide film
15
is used as a mask for carrying out a selective etching to the p-type cap layer
9
and an upper region of the p-type cladding layer
8
. A depth of the etching is an intermediate level of the p
Leung Quyen
NEC Corporation
Young & Thompson
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