Optical semiconductor device

Details Optical semiconductor device Optical semiconductor device

2000-01-04

2002-10-01

Davie, James (Department: 2828)

Coherent light generators

Particular temperature control

Heat sink

C372S031000

Reexamination Certificate

active

06459711

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical semiconductor device having both light emission and light reception and being used for optical information processing, optical measurement, optical communications and the like.
2. Description of the Related Art
In recent years, as optical semiconductor devices used for optical information processing, optical measurement, optical communication and the like, ones have come to be used in which a light source and a light receiving portion (photodetector) are provided in the same package.
A conventional optical semiconductor device will be described.
FIG. 19
is a plan view schematically showing a plane layout of the conventional optical semiconductor device.
FIG. 20
is cross-sectional view schematically showing the cross section of
FIG. 19
taken on the line
20
-
21
.
FIG. 21
is a cross section of
FIG. 19
taken on the line
21
—
21
.
In
FIGS. 19
,
20
and
21
, a semiconductor substrate
1
is made of, for example, Si, and has a rectangular concave portion
1
a
on the surface thereof. A semiconductor laser element
2
is made of, for example, GaAs, and acts as a light source for emitting signal detecting light. The semiconductor laser element
2
is mounted in the concave portion
1
a
so that the optical axis of the signal detecting light is substantially parallel to the surface of the semiconductor substrate
1
, and is integrated with the semiconductor substrate
1
.
The concave portion
1
a
is formed so that the signal detecting light from the semiconductor laser element
2
is reflected at the inclined side surface of the concave portion
1
a
that is opposed to the signal detecting light emitting side of the semiconductor laser element
2
in the direction substantially perpendicular to the surface of the semiconductor substrate
1
. In the part of the bottom surface of the concave portion
1
a
where the semiconductor laser element
2
is mounted, although not shown, one electrode for applying a voltage to the semiconductor laser element
2
is formed. The other electrode of the semiconductor laser element
2
is formed on the top surface of the semiconductor laser element
2
.
Light receiving portions
3
to
8
for signal detection are, for example, impurity diffused regions, and are formed outside the concave portion
1
a
on the surface of the semiconductor substrate
1
. For example, when the signal detecting light emitting side of the semiconductor laser element
2
on the surface of the semiconductor substrate
1
is the front side of the semiconductor laser element
2
, the light receiving portions
3
to
8
are selectively formed at the left and right sides of the concave portion
1
a.
The semiconductor substrate
1
and the light receiving portions
3
to
8
are opposite in conductivity type. Between the semiconductor substrate
1
and the light receiving portions
3
to
8
, a voltage that causes a reverse bias is applied.
A monitor region
12
is, for example, an impurity diffused region, is disposed in the rear of the concave portion
1
a
on the surface of the semiconductor substrate
1
, and detects the quantity of the signal detecting light from the semiconductor laser element
2
. The semiconductor substrate
1
and the monitor region
12
are opposite in conductivity type. Between the semiconductor substrate
1
and the monitor region
12
, a voltage that causes a reverse bias is applied. The impurity concentration of the monitor region
12
is approximately the same as that of the light receiving portions
3
to
8
.
In this optical semiconductor device, as shown by the arrow
9
in
FIG. 21
, the signal detecting light from the semiconductor laser element
2
is emitted in a direction substantially parallel to the surface of the semiconductor substrate
1
, and is reflected at the inclined side surface of the concave portion
1
a
situated in front to exit in a direction substantially perpendicular to the surface of the semiconductor substrate
1
.
The light receiving portions
3
to
8
are formed in positions outside the emission direction of the signal detecting light from the semiconductor laser element
2
in order that the carriers generated by the incidence of the signal detecting light from the semiconductor laser element
2
on the semiconductor substrate
1
do not adversely affect the signal detection levels of the light receiving portions
3
to
8
. For example, when the signal detecting light emitting side of the semiconductor laser element
2
is the front side of the semiconductor laser element
2
, the light receiving portions
3
to
8
are formed at the left and right sides of the semiconductor laser element
2
and at the left and right sides of the concave portion
1
a
on the surface of the semiconductor substrate
1
. The light receiving portions
3
to
8
may be formed in any positions that is in a periphery of the semiconductor laser element
2
, particularly outside the concave portion
1
a
. The number of light receiving portions is at least one.
The operation of the optical semiconductor device structured as described above will be described. First, the signal detecting light emitted from the semiconductor laser element
2
passes through an objective lens (not shown) and is condensed onto an optical recording medium (not shown). Consequently, the light corresponding to the signals of the optical recording medium is reflected and condensed onto the light receiving portions
3
to
8
, so that optical signals are output from the light receiving portions
3
to
8
. In this case, the quantity of the signal detecting light from the semiconductor laser element
2
is monitored by the monitor region
12
, and the semiconductor laser element
2
is controlled so that the quantity is constant.
In the structure of the above-described conventional example, the signal detecting light is emitted from the semiconductor laser element
2
in the direction shown by the arrow
9
, and unnecessary light (hereinafter, referred to as stray light) is generated in addition to the signal detecting light.
The stray light will be concretely described. The light associated with the optical semiconductor device includes the laser light emitted from the semiconductor laser element
2
(the light emitted from the front surface and the light emitted from the rear surface) and the return light by the reflection at a medium such as an optical disk or a magneto-optic disk. The light regarded as a problem in the present invention is the stray light due to the laser light emitted from the semiconductor laser element
2
.
Laser light includes light effective in signal detection and light ineffective in signal detection. Laser light is emitted so as to spread 180 degrees both in the vertical and the horizontal directions (the larger the angle is, the smaller the light quantity is). The light emitted frontward from the front surface of the semiconductor laser element
2
is the light effective in signal detection (signal detecting light). Light emitted in directions other than that (slanting directions, and directions just to the right and the left) is the light ineffective in signal detection. This ineffective light becomes stray light. When the stray light is applied to the semiconductor substrate
1
and is absorbed in the semiconductor substrate
1
, stray light carriers are generated.
The light emitted from the rear surface of the semiconductor laser element
2
also spreads 180 degrees both in the vertical and the horizontal directions (the larger the angle is, the smaller the light quantity is). Particularly, the light emitted rearward, that is, the light applied to the neighborhood of the monitor region
12
is used for detecting the light quantity of the semiconductor laser element
2
. Light emitted in directions other than that (slanting directions, and directions just to the right and the left) becomes stray light. Some of the carriers generated by the stray light being applied to the bottom surface or the side surfaces of the concave po

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