JPH02228080A - Semiconductor photodetector - Google Patents

Abstract

PURPOSE:To restrain the generation of current at a low level by doping the interfaces facing an optical absorption layer of a buffer layer and a window layer with impurities. CONSTITUTION:The interfaces facing an optical absorption layer 4 of a buffer layer 2a and a window layer 5a are doped with impurities such as Se, S, and Si. Namely, the carriers compensate for defects by doping the interfaces with impurities. As a result, a depletion layer ranges from the window layer 5a to the buffer layer 2a by applying a bias voltage, and the generation of current caused by defects or traps can be prevented even over the range including the both side interfaces of the optical absorption layer 4.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a semiconductor light-receiving device with an improved structure [Prior Art] A semiconductor light-receiving device having a light absorption layer of InGaAs has a wavelength of around 1.7μ ( It is widely used in 1-band wavelength optical communications because of its high light-receiving sensitivity up to
-1nP buffer layer (2), n-I nGaAs light absorption layer (4) and n-1nP window layer (5) are sequentially laminated, and then selectively from the surface of n-1nP window layer (5). Zn
A p''-Zn conductive layer (6) is formed by diffusing the p''-Zn conductive layer (6). On the surface of the n-~InP window layer (5), a SiNx surface protection film (7) is formed by diffusing the p''-Zn conductive layer (6). ) and the non-diffusion part. (8) is p” − of the light receiving area
P-electrode formed on the edge of the Zn conductive layer (6) and the SiNx surface protective film (7), (9) is the no-InP substrate (])
This is an n-electrode formed on the back surface.

In the above structure, a window layer that has a wider forbidden band than the light absorption layer and transmits light is provided on the E nGaAs P-based light absorption layer, and a pn junction is formed in the window layer. Therefore, in order to completely deplete the light absorption layer with a low bias, the carrier concentration of the window layer is also made as highly purified as that of the light absorption layer. Each layer is a high purity epitaxial layer, rnGaAs
The semiconductor light-receiving device with the above structure has been fabricated using the vapor phase growth method because the InP layer can be grown directly on the InP layer and the uniformity of the film thickness required to form a pn junction by diffusion is excellent. The surface protective film 6 uses SiNx instead of the oxide film in order to protect the pn junction on the surface of the window layer and prevent an increase in dark current due to surface oxidation.

[Problem to be solved by the invention]

However, the semiconductor light receiving element having the above structure has the following problems. That is, a) Defects at the double heterostructure interface are compensated for at high carrier concentrations (more than I In particular, in vapor phase growth, metamorphic layers are likely to form at interfaces, which act as traps and increase dark current.

) When a dielectric film is laminated as a surface protection film on a high-purity epitaxial layer, the charge of the dielectric film itself (SiNx
(if negative), a depletion layer is generated directly under the dielectric film and becomes a channel, or an interface state is generated at the interface between the dielectric film and the semiconductor, resulting in an increase in surface leakage current.

The present invention has been made in view of the above points.
The purpose is to provide a semiconductor light-receiving element with low dark current.

[Means and actions to solve the problem]

The present invention for achieving the above object is as follows. That is, in the present invention, a buffer layer, a light absorption layer, and a window layer of a first conductivity type are sequentially laminated on a semiconductor substrate of a first conductivity type, and a region of a second conductivity type is formed from the surface of the window layer toward the inside of the layer. is selectively formed, and a surface protective film is formed on the boundary region of the first conductivity type region and the second conductivity type region on the surface of the window layer, spanning the first conductivity type region and the second conductivity type region. In the semiconductor light receiving device, the first invention provides that impurities such as Se, S, and St are doped at the interfaces of the first pamphlet layer and the window layer facing the light absorption layer; The second invention is that the surface is doped with impurities.

n on the n--1nP buffer layer (2) by vapor phase epitaxy.
When growing a --1nCaAs light absorption layer, heating causes P in the n−1nP buffer layer to escape, creating a metamorphosed layer due to defects at the interface of the buffer layer on the light absorption layer side. Similarly n-
-11--111 p on the InGaAs light absorption layer (4)
When the n-InGaAs light-absorbing layer (4) is grown, As in the n-InGaAs light-absorbing layer (4) is grown, causing defects at the interface of the light-absorbing layer on the window layer (5) side. ) The interface between the buffer layer (2) and the window layer (5) facing the buffer layer (2) and the window layer (5) is doped with impurities to compensate for the above defects with carriers.As a result, by applying a bias voltage, the depletion layer closes to the window layer (5). From the buffer FJ (2) to the buffer FJ (2), it is possible to prevent current generation due to defects and traps even over a range including both interfaces of the light absorption layer (4). Doping with impurities can prevent the formation of channels on the surface of the window layer (5) due to the charges of the surface protection film (7) made of a dielectric material, and can suppress surface leakage. The impurity-doped layer formed at the interface between layer (2) and window N(5) has a carrier concentration of 5.OXl0ISe11-' ~
1. OXIO"CI-' range, thickness 0.1~
It is desirable that the thickness is 0.3 μ because the carrier concentration is 1.0×10” CI-’ or more or the thickness is 0
．． When it is 3- or more, dark current due to tunneling phenomenon increases. In addition, the carrier concentration is 5×10”am-’ or less,
Alternatively, if the thickness is less than 0.1, trap defects cannot be compensated for.

〔Example〕

The present invention will be described below based on embodiments shown in the drawings.

FIG. 1 is a sectional view of a main part of an embodiment of a semiconductor light-receiving device according to the present invention, in which an n--1nP buffer layer (2a) and an n- 1nP
Doping layer (2b), n--1nGaAS optical absorption N(
4) Sequentially grow an n-1nP doped layer (5b), an n-InP window layer (5a), and an n-1nP doped layer (5c). Buffer 1it (2a) and window layer (5a)
The impurity concentration is 1.0X10"cm-" and the thickness is 2.0-
1n-1nP doping layer (2b), (5b), (5C
) has an impurity concentration of 7.0X10"CI-" and a thickness of 0.2
n, the light absorption layer (4) has an impurity concentration of 5.0×10”el
A p-type conductive layer (6) is selectively formed on the surface of the window layer (5a) with a thickness of 265 mm by thermal diffusion of Zn, Cd, and Mg, or by ion implantation of Be and Mg. A pn junction is formed in the window layer (5a), and a dielectric layer made of SiNx is formed on the doping layer (5C).
! A film (7) is formed. (8) is T i / P t
/ Au n electrode, (9) is AuGeNi/Au n electrode
The t-pole (00) is an AR film covering a light-receiving portion with a light-receiving diameter of 100-φ. When a bias voltage of 5cm was applied to the semiconductor photodetector of this example, the edge of the depletion layer reached the buffer layer (2a), and the light absorption layer (4) was completely depleted. When light is incident in this state, more than 90% of quantum Efficiency was achieved. In addition, under a bias voltage of 5■, the dark current was less than 1 nA, and the frequency response was more than IGHz. Incidentally, in the case without the doped layer in this example, the quantum efficiency was 70%, the dark current was 10 nA or more, and the frequency response was 500 MHz.

Note that the window layer and buffer layer are lattice matched to the light absorption layer,
It is sufficient if the material has a wider forbidden band width than the light absorption layer, and for the InGaAs light absorption layer in the above embodiment, I
InGaAsP may be used other than nP, and
The present invention can also be applied to compound semiconductors other than InGaAsP-based, such as GaSb-based. Furthermore, although the above embodiments are about planar type PIN photodiodes, the present invention can also be implemented with mesa type photodiodes, and can also be implemented with avalanche photodiodes. It goes without saying that the light absorption layer is not limited to a bulk semiconductor, and can also have a quantum well structure.

〔Effect of the invention〕

As explained above, according to the present invention, impurities are doped at the interfaces of the buffer layer and the window layer facing the light absorption layer, and at the surface of the window layer on the light incident side.
! 12it and surface leakage current can be suppressed to a low level, and a good semiconductor light-receiving element with small dark current can be obtained, which is an excellent effect.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a main part of an embodiment of a semiconductor light receiving element according to the present invention, and FIG. 2 is a sectional view of a main part of a conventional example. 1...Substrate, 2,2a...Buffer layer, 2b,
5b5c... Doping layer, 4... Light absorption layer, 5.5a... Window layer, 6... Conductive layer, 7.
...Surface protective film, 8...n electrode, 9...n electrode, 10...AR film. Figure 2

Claims (2)

[Claims] (1) A first conductivity type buffer layer, a light absorption layer, and a window layer are sequentially laminated on a first conductivity type semiconductor substrate, and a second conductivity type region is selected from the surface of the window layer toward the inside of the layer. A semiconductor light-receiving element in which a surface protection film is formed on the boundary region between the first conductivity type region and the second conductivity type region on the surface of the window layer and spanning the first conductivity type region and the second conductivity type region. In the interface of the buffer layer and the window layer facing the light absorption layer,
A semiconductor light-receiving element characterized by being doped with impurities. (2) The semiconductor light-receiving device according to claim 1, wherein the surface of the window layer on the light incident side is doped with an impurity.