Semiconductor laser device

Details Semiconductor laser device Semiconductor laser device

2002-12-02

2004-07-20

Davie, James W. (Department: 2828)

Coherent light generators

Particular active media

Semiconductor

Reexamination Certificate

active

06765944

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser device and, more particularly, to a ridge waveguide type semiconductor laser device.
2. Description of the Background Art
There are semiconductor laser devices having various structures. In particular, it is noted that some semiconductor laser devices have a channel waveguide having a refractive index structure for confining light in an active layer in a horizontal direction parallel to the layer. For example, a ridge waveguide type semiconductor laser device is a channel waveguide type semiconductor laser device. The ridge waveguide type semiconductor laser device has a ridge portion (that is, projection portion) projected from the peripheral cladding layer such that current is injected into the ridge portion for laser oscillation.
The ridge waveguide type semiconductor laser device will be described below with reference to
FIGS. 1
to
3
. As shown in
FIGS. 1 and 2
, the semiconductor laser device
60
has a stacked structure including a first electrode
56
a
, an n-type GaAs substrate
51
, an n-type AlGaInP first cladding layer
52
, an active layer
53
, a p-type AlGaInP second cladding layer
54
, an insulating layer
55
, a p-type GaAs contact layer
57
, and a second electrode
56
b
. The active layer
53
has multiple quantum wells (hereinafter referred to as MQW) structure. The second cladding layer
54
has a projection portion
58
that projects. The insulating layer
55
covers the portion except for the top thereof, and it is made of a silicon nitride (SiN) layer having a layer thickness of 100 nm. The second electrode
56
b
is electrically connected to the top of the projection portion
58
of the second cladding layer
54
through the contact layer
57
. The first and second electrodes
56
a
and
56
b
are made of a metal such as AuGe/Ni/Au and Ti/Au, respectively. In addition, a window region
59
is formed by diffusion of zinc atoms within the active layer
53
, adjacent to a facet of the semiconductor laser device
60
. A laser beam
62
is output to the outside through the end-face window region
59
.
FIG. 3
shows optical output dependency of a far field pattern (hereinafter referred to as FFPx) in a direction parallel to a p-n junction plane of the conventional ridge waveguide type semiconductor laser device. As shown in
FIG. 3
, a half width of FFPx is increased as the optical output is increased. There is a relatively large difference of about 2° between half widths of FFPx at an output of 5 mW and at an output of 50 mW (hereinafter referred to as &Dgr;FFPx). It is noted that the half width of FFPx at 50 mW is measured but FFPx at 50 mW isn't shown in the figure. When the optical output is changed, if &Dgr;FFPx is large, optical design in an application device such as a DVD-R drive becomes disadvantageously complicated.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a semiconductor laser device in which &Dgr;FFPx is not changed largely even when optical output thereof is changed.
In accordance with one aspect of the present invention, there is a semiconductor laser device including a stacked structure. The stacked structure includes a first electrode, a substrate of first conduction type layered on the first electrode, a first cladding layer of the first conduction type, an active layer, a second cladding layer of second conduction type opposite to the first one, an insulating layer, and a second electrode. The second cladding layer is deposited on the active layer. The second cladding layer includes at least first and second portion having thickness different from each other. The first portion is thicker than the second portion. The first portion is referred to as projection portion. The insulating layer is deposited on the second cladding layer except for the first portion. The second electrode electrically is connected to the first portion of the second cladding layer, and is deposited on the insulating layer. In the insulating layer, a product of a reciprocal of a layer thickness and a heat conductivity of the insulating layer is smaller than 4×10
8
W/(m
2
K).


REFERENCES:
patent: 2002/0159494 (2002-10-01), Tojo et al.
patent: 2003/0091082 (2003-05-01), Fukunaga
Miyashita, M. et al.; “High-Power Operation of Low-Operating-Current 660nm Laser Diodes for DVD-RAM/RW”, OECC/IOOC 2001 Conference Incorporating ACOFT, Jul. 2-Jul. 5, 2002.

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