Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Responsive to electromagnetic radiation
Reexamination Certificate
1999-12-07
2001-05-15
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Responsive to electromagnetic radiation
C438S295000, C438S429000, C438S067000, C438S093000, C438S699000, C438S702000
Reexamination Certificate
active
06232141
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a semiconductor light-receiving device to be employed for optical communication and optical data processing, and a method of fabricating the same.
2. Description of the Related Art
A compound semiconductor light-receiving device has been put to practical use as a wide-range wavelength light receiver with high sensitivity for optical communication and optical data processing. Above all, a semiconductor light-receiving device for a wavelength of 1.3 &mgr;m or 1.55 &mgr;m, which is a wavelength for high capacity long-distance optical communication, is usually made of InGaAs.
It is necessary for a PIN photo diode made of InGaAs to minimize a junction capacity of individual devices in order to accomplish ultra-high speed response greater than 40 Gbps, and to form a light-absorbing layer thinner in order to reduce running time of carriers.
However, in a presently commercially available light-receiving device having a surface through which the device receives a light, if a light-receiving diameter is made smaller for reducing a junction capacity, optical coupling would be difficult to properly take place when the light-receiving device receives a light from an optical fiber, resulting in deterioration of coupling efficiency. On the other hand, if a light-receiving layer made of InGaAs were formed thinner, it would be possible to reduce running time of carriers, however, with the result of reduction in quantum efficiency. Thus, reduction in a junction capacity and enhancement in coupling efficiency, and reduction in carrier running time and enhancement in quantum efficiency are in a trade-off relationship. Hence, since a direction in which a light is directed is coaxial with a direction in which carriers run in either process, reduction in light-receiving sensitivity is unavoidable, even if high-speed response could be accomplished.
In order to avoid influence due to the above mentioned trade-off relationship, there has been suggested a waveguide type light-receiving device in which a direction in which a light runs is deflected by 90 degrees to a direction in which carriers run.
FIG. 1
illustrates one of conventional waveguide type light-receiving devices, which has been suggested by K. Kato et al. in “High efficiency, waveguide InGaAs pin photodiode with bandwidth of 40 GHz”, Electronic Data Communication Association Spring Conference, 1991, pp. 4-200, C-183. The illustrated waveguide type light-receiving device includes a semi-insulating InP substrate
20
, an insulating layer
21
formed on the substrate
20
, a waveguide type light-receiving region
22
formed on the insulating layer
21
, a pair of polyimide layers
23
sandwiching the light-receiving region
22
therebetween, a p-side electrode
24
formed over the light-receiving region
22
and the polyimide layers
23
, and an n-side electrode
25
formed on the insulating layer
21
. The waveguide type light-receiving region
22
acts as a waveguide, and is comprised of an n-InGaAsP clad layer
22
a,
an n-InGaAs light-absorbing layer
22
b,
a p-InGaAs light-receiving layer
22
c,
a p-InGaAsP clad layer
22
d,
and a p-InGaAsP contact layer
22
e.
The waveguide type light-receiving region
22
is formed by successive, epitaxial growth of these layers. The p-side electrode
24
makes electrical contact with the p-InGaAsP contact layer
22
e,
and the n-side electrode
25
makes electrical contact with the n-InGaAsP clad layer
22
a.
The polyimide layers
23
sandwiching the light-receiving region
22
therebetween to thereby reduce a capacity of a bonding region.
In the illustrated waveguide type light-receiving device, a light is introduced into the device through an end surface of the light-receiving region
22
, and is transferred and absorbed in the n-InGaAs light-absorbing layer
22
b
and the p-InGaAs light-absorbing layer
22
c
both vertically sandwiched between the clad layers
22
d
and
22
a.
Carriers generated due to absorption of a light are transferred to an external circuit (not illustrated) through the p-InGaAsP clad layer
22
d,
p-InGaAsP contact layer
22
e,
and p-side electrode
24
. Since absorption of a light is accomplished in a length-wise direction of the light-receiving region
22
, it is possible to obtain high quantum efficiency. In addition, since carriers run perpendicularly to the light-receiving region
22
, running time of carriers is dependent only on a thickness of the n-InGaAs light absorbing layer
22
b.
The above mentioned waveguide type light-receiving device has a problem as follows. If the n-InGaAs light absorbing layer
22
b
is formed thinner for reducing carriers running time, optical coupling efficiency would be deteriorated because a light introduced into the device through an optical fiber has a greater diameter than a thickness of the n-InGaAs light absorbing layer
22
b.
In contrast, if the n-InGaAs light absorbing layer
22
b
is formed thicker for enhancing optical coupling efficiency, it would be accompanied with an increase in running time of carriers.
FIGS. 2A
to
2
C illustrate another semiconductor waveguide light-receiving device suggested in Japanese Unexamined Patent Publication No. 3-35555.
FIG. 2A
is a top plan view of the device,
FIG. 2B
is a cross-sectional view of the device taken along the line IIB—IIB in
FIG. 2A
, and
FIG. 2C
is a cross-sectional view of the device taken along the line IIC—IIC in FIG.
2
A.
The illustrated semiconductor waveguide light-receiving device includes a semiconductor substrate
30
, a buffer layer
31
formed on the substrate
30
, a waveguide
32
formed partially on the buffer layer
31
, a light-receiving layer
33
, and a junction forming layer
34
. The waveguide
32
, the light-receiving layer
33
, and the junction forming layer
34
are sandwiched by fillers
35
. The light-receiving layer
33
and the junction forming layer
34
cooperate with each other to form a light-receiving device, and are formed tapered in a direction indicated with an arrow X in which a light is directed. On the junction forming layer
34
are alternately formed p-type regions
36
a
and n-type regions
36
b
arranged in a direction indicated with the arrow X.
A light is introduced into the device through an end surface
37
thereof, and is transferred through the waveguide
33
in a direction indicated with the arrow X.
FIG. 3
illustrates still another semiconductor waveguide light-receiving device suggested in Japanese Unexamined Patent Publication No. 4-268770.
The illustrated device includes an InP substrate
40
, an InGaAsP clad layer
41
formed on the substrate
40
, an InGaAsP core layer
42
formed on the InGaAsP clad layer
41
, clad layers
43
and
44
both made of an InGaAsP multi-layered structure formed on the InGaAsP core layer
42
, an InGaAsP layer
45
formed on the InGaAsP core layer
42
, an n-side electrode
46
formed on a lower surface of the substrate
40
, and a p-side electrode
47
formed on an upper surface of the InGaAsP layer
45
. The multi-layered structure
43
and
44
are formed by alternately depositing layers for absorbing a light thereinto and layers transparent to a light. The multi-layered structure
44
is formed partially on the multi-layered structure
43
in the form of a ridge.
The multi-layered structures
43
and
44
act as a light-absorber. A light is introduced into the device through a side surface thereof in a direction indicated with an arrow X, and is converted into electricity in the multi-layered structures
43
and
44
.
In both of the above mentioned waveguide light-receiving devices, a light is introduced into the devices through end surfaces thereof. However, the devices have a problem that optical coupling efficiency is quite low. In the above mentioned conventional waveguide light-receiving devices, if an n-InGaAs light-receiving layer is formed thinner for reducing running time of carriers, optical coupling efficiency would be deteriorated because an incident light has a sufficiently greater
NEC Corporation
Rocchegiani Renzo N.
Smith Matthew
Young & Thompson
LandOfFree
Semiconductor light-receiving device and method of... 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 light-receiving device and method of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor light-receiving device and method of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2487213