JPS6346783A - Photoconductive semiconductor photo-detector - Google Patents

Abstract

PURPOSE:To obtain high speed responding characteristic of a semiconductor photodetector by reducing carrier concentration conductivity type semiconductor electrode lower than that of a carrier moving region only near the side of the electrode where minority carrier reaches. CONSTITUTION:After an n<-> type InGaAs layer 2 is crystal-grown on a semi- insulating InP substrate 1, the layer 2 out of a photodetecting region is removed by mesa etching. After an SiO2 film 5 is then formed, the region 5 of a specific region near a source is removed in a photoresist forming step. With the photoresist and the film 5 as masks Be<++> ions are implanted to a selected region, and an n<--> type InGaAs region 6 reduced in carrier concentration by compensating is formed by annealing. Then, a source electrode 4 and a drain electrode 3 are formed by depositing in vacuum AuGeNi and heat treating it. Thus, holes accelerated by an internal potential near the electrode 4 can be exhausted to the electrode at a high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a photoconductive semiconductor light-receiving element used in optical communications, optical information processing, and the like.

[Conventional technology]

Compound semiconductor light-receiving elements are used in optical receivers for optical communications or optical information processing, and the development of high-speed, high-intensity elements is being actively pursued. Among them, photoconductive semiconductor light-receiving elements do not have a depletion layer (i.e., capacitance) in the carrier travel region unlike diode-type light-receiving elements. There is an expectation that high gain bandwidth product (high GB product) characteristics can be obtained by designing the device so that the time is shortened.

In the 1.0-1.6 μm wavelength band, which is the low-loss band of optical fibers that are attracting attention for optical communications, InGaAS is the most suitable material for semiconductor light-receiving elements. An example of the basic structure of a conventional InGaAs-based photoconductive semiconductor light receiving element is shown in FIG. This structure is an element fII structure in which an n--T nGaAs layer 2 is crystal-grown on a semi-insulating 1nP substrate 1, and two electrodes 3.4 are formed on the surface of this semiconductor layer 2, which is mesa-etched. have.

A voltage is applied between the picture electrodes 3 and 4, and the conductivity increases due to the photoexcited carriers incident therebetween, thereby converting the optical signal into an electrical signal.

Here, in the case of an n-type semiconductor, the internal current gain is G-τ/l
・・・・・・・・・(1) τ: Positive-hole lifetime; Determined from electron transit time. In the case of transit time limitation, the lifetime τ becomes the transit time of holes, so the current gain G is determined by the ratio of the transit times of holes and electrons. (2) In a V group compound semiconductor, the electron travels faster than the hole, so the gain G is always greater than 1.

[Problem that the invention seeks to solve]

However, the above-mentioned conventional photoconductive semiconductor light-receiving device has a drawback in that its response speed is limited by the slow traveling speed of holes. In particular, when considering holes traveling between electrodes, although they feel a strong electric field and drift near the drain electrode (+ electrode), they experience a very weak electric field near the source electrode (- electrode). It cannot go out to the electrode at high speed. This limited the effective transit time of the holes and was a cause of response deterioration (J, C, Gamme
lDoctoral dissertation, p122. (See Cornell University, 1980).

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks and to provide a photoconductive semiconductor light-receiving element in which holes exit to the electrode at high speed under a weak electric field near the source electrode, that is, the photoconductive semiconductor light-receiving element has high-speed response characteristics.

[Means for solving problems]

The present invention has a pair of electrodes on the surface of a conductive type semiconductor in which electrons and holes, whichever has a faster traveling speed, is the majority carrier, and an electric field applied between the electrodes moves carriers into the conductive type semiconductor. In a photoconductive semiconductor light-receiving element that travels in a direction parallel to the surface of the conductive semiconductor, only the vicinity of the side of the electrode of the semiconductor of the conductivity type where the minority carriers reach is made to have a lower carrier concentration than the region where the carriers travel. It is characterized by the fact that

[Effect]

The present invention solves the problems of conventional photoconductive semiconductor light-receiving elements by adopting the above-described configuration. That is, in the photoconductive semiconductor light-receiving element according to the present invention, for example, an example in which the majority carriers having a faster traveling speed are electrons:
By lowering the carrier concentration near the source electrode (near the area where holes exit the semiconductor) in an n-type semiconductor than in the carrier travel region, an internal potential that works to cause holes to drift at high speed due to the diffusion potential. occurs. This internal potential provides high-speed response characteristics. This holds true even if the roles of electrons and holes are reversed.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram showing the cross-sectional structure of a photoconductive semiconductor light-receiving element according to an embodiment of the present invention. According to this embodiment, the carrier concentration on the semi-insulating InP substrate 1 is ~2 x 10''
After crystal growth of ~1.5 μm of csduno-I nGaAs 2, InG outside the light-receiving area was removed by mesa etching.
Remove aAs2. Next, after forming the 5i02 film 5, a photoresist process is performed to form the 5i02 film 5 in a specific region near the source.
Remove i02 film 5. Furthermore, this photoresist and Si○2
Using the film 5 as a mask, Be- is ion-implanted into a selected region and annealing is performed to form an n--InGaAs region 6 whose carrier concentration is lowered by compensating. Next, the source electrode 4 and the drain electrode 3 are made of AuGeN.
It is formed by vacuum evaporation of i and heat treatment.

n--InGaAs2 near the source of the device thus obtained
A schematic band diagram at the n---I nGaAs interface is shown in FIG. 2. The internal potential created by the diffusion potential exerts a force on the holes that causes them to drift toward n--InGaAs. In this way, holes accelerated by the internal potential near the source electrode 4 can go out to the electrode at high speed.

In the above embodiment, ion implantation was used to form the n- region by compensit, but it may be formed by other methods such as impurity thermal diffusion.

[Effects of the Invention] As explained above, according to the present invention, the transit time of holes can be substantially improved, and a photoconductive semiconductor light-receiving element having high-speed response characteristics can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the cross-sectional structure of a photoconductive semiconductor light-receiving device according to an embodiment of the present invention, and FIG.
FIG. 3 is a schematic diagram of a cross-sectional structure of a conventional photoconductive semiconductor light-receiving element. In the figure, 1 is a semi-insulating InP substrate, 2 is an n--I n
GaAs, 3 is a train electrode, 4 is a source electrode, 5 is S
i 02 FIJ,, 6 is n-1-InGaAs\Fly, Figure 3, Figure 2

Claims (1)

[Claims] A pair of electrodes is provided on the surface of a semiconductor of a conductivity type in which electrons and holes, whichever has a faster traveling speed, is the majority carrier, and an electric field applied between the electrodes causes carriers to be moved parallel to the surface of the semiconductor of the conductivity type. In a photoconductive semiconductor light-receiving element that travels in a direction, only the vicinity of the side of the electrode of the semiconductor of the conductivity type where the minority carriers reach is made to have a lower carrier concentration than the region in which the carriers travel. Features of photoconductive semiconductor light-receiving device.