Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Reexamination Certificate
2001-12-27
2004-06-22
Baumeister, B. William (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
C257S436000, C257S447000, C257S458000, C257S460000
Reexamination Certificate
active
06753587
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to semiconductor devices, and more particularly, to semiconductor photo detecting devices for an application of optical fiber communication systems and optical information processing devices, and manufacturing method of the device.
2. Description of the Related Art
Semiconductor photo detecting devices convert a photo signal into an electric signal, and are essential components in optical fiber communication systems. A recent increase in traffic through optical fiber communication systems, accompanied by an increase in communication speed, demands a further increase in a response speed of semiconductor photo detecting devices.
PIN photo diodes are widely used as conventional high speed semiconductor photo detecting devices. A PIN photo diode includes a photo absorption layer where an incoming photo signal generates photo-excited carriers thereof. The carriers are output as a photo-electric current through a reverse biased p-n junction. The PIN photo diode is capable of high speed response.
A response speed of the PIN photo diode is, however, restricted by a parasitic capacitance of the p-n junction. Various configurations claiming to reduce the parasitic capacitance are proposed successfully.
As configuration improvements reduce the parasitic capacitance of the PIN photo diode, a carrier movement time in which photo-excited carriers move through the photo absorption layer is drawing attention as another restriction in response speed. By reducing a thickness of the photo absorption layer of the PIN photo diode, the carrier movement time can be reduced, but more incoming photo signal passes through the layer. Since the incoming light is not absorbed sufficiently, a less efficiency of photo detection becomes another problem.
To avoid this dilemma, a PIN photo diode which receives a photo signal at an inclined incidental angle to the slim photo absorption layer to reduce the carrier movement time and, at the same time, to increase the photo detection efficiency, is proposed.
FIG. 1
shows a configuration of a high speed PIN photo diode
10
using a conventional technology.
As shown in
FIG. 1
, the PIN photo diode
10
is formed on a semi-insulating InP substrate
11
, and includes an n-type InP buffer layer
12
grown by epitaxial growth technique on the InP substrate, a non-doped or n
−
-type InGaAs photo absorption layer
13
grown by epitaxial growth technique on the buffer layer
12
, a p-type InP cap layer
14
grown by epitaxial growth technique on the photo absorption layer
13
. An n-type ohmic electrode
12
A is formed on the n-type InP buffer layer
12
, and p-type ohmic electrode
14
A is formed on the p-type InP cap layer.
In case of the configuration shown in
FIG. 1
, the n-type InP buffer layer
12
forms a pattern of a limited area on the InP substrate
11
, and the photo absorption layer
13
and p-type InP cap layer
14
also form a mesa structure of a limited area on the n-type InP buffer layer
12
, and a parasitic capacitance of the configuration is consequently minimal. Further, in case of the PIN photo diode, an incoming photo signal
1
comes to a bottom face
11
A of the InP substrate
11
at an inclined incidental angle of &thgr;
o
, and is refracted at a refraction angle &thgr;
i
. The photo signal passes through the photo absorption layer
13
at an inclined angle.
In case of a photo diode that requires an incoming photo signal passing through the substrate bottom face
11
A at an inclined angle, even if the incoming photo signal comes to the substrate bottom face
11
A at a big incidental angle &thgr;
o
, the photo signal passes through the photo absorption layer
13
substantially perpendicularly due to a very high refraction rate, about 3.0, of the InP substrate
11
. An optical path in the absorption layer
13
is not long enough.
FIG. 2
shows another configuration of a high speed PIN photo diode
20
using a conventional technique, which is described in a Japanese Patent Laid-open Application No. 11-135823.
As shown in
FIG. 2
, the PIN photo diode
20
is formed on a semi-insulating InP substrate
21
, and includes an n-type InP buffer layer
22
grown by epitaxial growth technique on the InP substrate
21
, an n
−
-type InGaAs photo absorption layer
23
grown by epitaxial growth technique on the InP buffer layer
22
, a n-type InP cap layer
24
grown by epitaxial growth technique on the photo absorption layer
23
. A doped p-type diffusion region
25
is formed in the InP cap layer
24
and a portion of the InGaAs photo absorption layer
23
thereof.
A p-type ohmic electrode
26
connected to the p-type diffusion region
25
is formed on the InP cap layer
24
, and n-type ohmic electrode
27
is formed on an n-type region outside the p-type diffusion region
25
. An exposed surface of the InP cap layer
24
is covered by a passivation film
24
A such as SiN.
In case of the PIN photo diode
20
shown in
FIG. 2
, a portion of semiconductor layers
22
-
24
including the substrate
21
is removed by etching from a side. The PIN photo diode
20
has a side face
21
A of the substrate
21
and a slope
21
B connected to the side face
21
A and cutting the semiconductor layers
22
-
24
at an inclined angle. If a photo signal
1
comes to the slope
21
B in parallel to the substrate
21
, the photo signal
1
is refracted at the slope
21
B toward the photo absorption layer
23
.
A configuration similar to the PIN photo diode
20
shown in
FIG. 2
is described in a Japanese Patent Laid-open Application No. 11-307806.
FIG. 3
shows a configuration of a PIN photo diode
30
described in the Japanese Patent Laid-open Application No. 11-307806. In
FIG. 3
, portions described previously are referred by the same numerals as before.
As shown in
FIG. 3
, the PIN photo diode
30
is formed on a n-type InP substrate
31
, and includes an n
−
-type InGaAs photo absorption layer
32
grown by epitaxial growth technique on the substrate
31
, and an n-type InP cap layer
33
grown by epitaxial growth technique on the photo absorption layer
32
. A p-type doped diffusion region
34
is formed in the InP cap layer
33
and a portion of the InGaAs photo absorption layer thereof. A p-type ohmic electrode
35
is formed on the p-type diffusion region
34
, and n-type ohmic electrode
36
is formed on a bottom principal plane
31
A of the InP substrate
31
.
In case of the PIN photo diode
30
shown in
FIG. 3
, a slope
31
B is formed at the bottom of the InP substrate
31
. A photo signal
1
coming in parallel to the bottom face of the substrate
31
is refracted toward the photo absorption layer
32
.
It should be noted that a direction of an incoming photo signal can be changed not only by refraction but also by a reflection.
FIG. 4
shows a configuration of a PIN photo diode
40
described in a Japanese Patent Laid-open Application No. 2000-183390. This configuration utilizes a reflection of an incoming photo signal.
As shown in
FIG. 4
, the PIN photo diode
40
is formed on a semi-insulating InP substrate
41
, and includes an n-type InP buffer layer
42
grown by epitaxial growth technique on the InP substrate
41
, an n
−
-type InGaAs photo absorption layer
43
grown by epitaxial growth technique on the buffer layer
42
, a n-type InP cap layer
44
grown by epitaxial growth technique on the photo absorption layer
43
. A p-type diffusion region
45
is formed in the InP cap layer
44
and a portion of the InGaAs photo absorption layer
43
thereof. A p-type ohmic electrode
46
is formed on the p-type diffusion region
45
, and n-type ohmic electrode
47
is formed on the n-type region of the InP cap layer
44
.
A concavity
41
A shaped by a slope is formed on the bottom principal plane of the InP substrate
41
. An incoming photo signal
1
passes through a side face of the InP substrate
41
in parallel to the bottom principal plane, and is reflected toward the photo absorption layer
43
by the slope shaping the concavity
41
A. Th
Furuya Akira
Shirai Tatsunori
Baumeister B. William
Fujitsu Quantum Devices Limited
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