Semiconductor photodetection device

Details Semiconductor photodetection device Semiconductor photodetection device

2001-12-17

2004-02-17

Eckert, George (Department: 2815)

Active solid-state devices (e.g., transistors, solid-state diode

Responsive to non-electrical signal

Electromagnetic or particle radiation

C257S431000, C257S446000, C257S452000, C257S458000, C257S462000

Reexamination Certificate

active

06693337

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATION
The present application is based on Japanese priority applications No. 2001-302109 filed on Sep. 28, 2001 and No. 2000-386036 filed on Dec. 19, 2000, the entire contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The present invention generally relates to optical semiconductor devices and more particularly to a semiconductor photodetection device used especially for fiber optics communication system.
FIG. 1
shows in general the structure of a conventional semiconductor photodetection device
10
of the type that receives incoming optical signal at a substrate surface side.
Referring to
FIG. 1
, the semiconductor photodetection device
10
is constructed on a substrate
11
of n-type InP, and includes a layer structure having an n-type InGaAs optical absorption layer
12
with low carrier concentration formed on the substrate
11
and a cap layer
13
of n-type InP formed on the layer
12
. A p-type InGaAs region
16
and p-type InP region
15
are formed in the InGaAs optical absorption layer
12
and the n-type InP cap layer
13
by introducing a p-type impurity through an opening, which has been patterned in a dielectric protection layer
14
formed on the cap layer
13
. An n-type electrode
17
is formed on the n-type InP substrate
11
and a p-type contact electrode
18
is formed on the p-type InP region
15
, respectively. In the n-type electrode
17
is formed an optical window, through which an optical signal passes. In this illustrated embodiment, an antireflection film
19
is formed at the optical window on the substrate
11
.
In operation of the photodetection device
10
shown in
FIG. 1
, a reverse bias voltage is applied between the electrodes
17
and
18
. Under this condition, an optical signal having a wavelength of 1260-1620 nm used for fiber optics communication enters into the substrate
11
through the optical window. Because the substrate InP layer
11
is transparent to the light having the above wavelength, the incident signal light reaches the InGaAs optical absorption layer
12
without being absorbed by the substrate
11
, and there occurs excitation of photocarriers in the optical absorption layer
12
.
The frequency response of such a semiconductor photodetection device is generally determined by a time constant CR and a transit time of the carrier excited by the incident light, where C is a capacitance and R is an internal resistance of the device. In order to improve the frequency response of the semiconductor photodetection device
10
, the time constant needs to be shortened and the carrier transit time also needs to be shortened. Because the carrier transit time increases proportionally to the thickness of the InGaAs optical absorption layer
12
, it should be reduced in thickness, as much as possible in order to shorten the carrier transit time to improve the frequency response.
However, if the thickness of the InGaAs optical absorption layer
12
is reduced with the aim of achieving high speed, the optical absorption layer
12
can not absorb the incident light sufficiently, which degrades the quantum efficiency of the optical absorption.
Thus, because there exists a trade-off relationship between the frequency response and the quantum efficiency, it is difficult to obtain the optimum thickness of the InGaAs optical absorption layer
12
when designing semiconductor photodetection devices requiring high-speed response.
In order to solve this efficiency problem, in the conventional semiconductor photodetection device
10
of the substrate-side incident type shown in
FIG. 1
, the signal light that has not been absorbed by the optical absorption layer
12
is reflected by the p-type contact electrode
18
and re-introduced into the optical absorption layer
12
through the InP cap layer
13
to avoid the reduction in the quantum efficiency.
In the semiconductor photodetection device
10
shown in
FIG. 1
, while a metal layer constituting the contact electrode
18
is vapor-deposited on the n-type InP cap layer
13
, heat resulting from the vapor-deposition forms an alloy metal layer at the interface between the InP cap layer
13
and the metal contact electrode
18
. As a result, the planarity of the interface between the InP cap layer
13
and the contact electrode
18
is degraded. This degradation of planarity significantly lowers the reflectivity of the interface and reduces the amount of the signal light reflected by the interface, and therefore the signal light is mostly scattered by the interface and cannot be absorbed well enough in the InGaAs optical absorption layer
12
. Consequently, the quantum efficiency is lowered and the amount of light returning from the photodetection device
10
to an optical fiber is increased, resulting in lower the transmission characteristics of fiber optics communication system.
In order to deal with the above mentioned problem, there has been a proposal, in Japanese Laid-Open Patent Publication 5-218488, that a dielectric layer
20
be interposed between the cap layer
13
and the contact electrode
18
as shown in
FIG. 2
, and would inhibit the alloying reaction between the metal layer of the contact electrode
18
and the InP layer of the cap layer
13
. Similar or the same parts in
FIG. 2
corresponding to the previously described parts in
FIG. 1
are designated by the same reference numerals and the description thereof will be omitted.
This conventional structure of the substrate side incident type semiconductor photodetection device shown in Japanese Laid-Open Patent Publication 5-218488, however, has suffered from problem in that the contacting area between the contact electrode
18
and the InP cap layer
13
is reduced because of the dielectric layer
20
, and the adherence between the metal layer of the contact electrode
18
and the dielectric layer
20
is not strong enough. Therefore, there has been a problem that the contact electrode
18
peels off during the manufacturing process, wire bonding process or flip chip mounting process.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of the present invention to provide a novel and useful semiconductor photodetection device wherein the foregoing problems are eliminated.
Another and more specific object of the present invention is to provide a reliable semiconductor photodetection device having high speed response and high efficiency.
Another object of the present invention is to provide a semiconductor photodetection device, comprising:
a semiconductor structure including an optical absorption layer having a photo-incidence surface on a first side thereof;
a dielectric reflecting layer formed on a second side of the semiconductor structure opposite to the first side;
a contact electrode surrounding the dielectric reflecting layer and contacting with the semiconductor structure; and
a close contact electrode covering the dielectric reflecting layer and contacting with the contact electrode and the dielectric reflecting layer, the close contact electrode adhering to the dielectric reflecting layer more strongly than to the contact electrode.
Another object of the present invention is to provide a semiconductor photodetection device, comprising:
a semiconductor structure including an optical absorption layer having a photo-incidence surface on a first side thereof;
a dielectric reflecting layer formed on a second side of the semiconductor structure opposite to the first side;
a contact electrode surrounding the dielectric reflecting layer and contacting with the semiconductor structure;
a dielectric coating layer surrounding the contact electrode; and
a close contact electrode covering the contact electrode and the dielectric coating layer and contacting with the contact electrode and the dielectric coating layer, the close contact electrode adhering to the dielectric coating layer more strongly than to the contact electrode.
It is preferable to form the semiconductor photodetection device so that the dielectric reflecting layer and the dielectric coatin

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