JPS62245684A - Photoconductive semiconductor photodetector - Google Patents

Abstract

PURPOSE:To manufacture the title photodetector with high gain band width space by a method wherein the main carrier arresting level is set up only on the specific region near the electrode on the main carrier reaching side on the surface of a conductivity type semiconductor using the main carrier at high running speed. CONSTITUTION:An N<->-InGaAs 2 is deposited on a semiinsulating InP substrate 1 while a source electrode 4 and a drain electrode 3 are formed by evaporating AuGeNi and heat-treatment. The InGaAs 2 excluding the photodetector region is removed by mesa etching process. Next, an SiO2 film 5 is formed while an opening is made in a specific part near the source electrode 4 to form a damage region by implanting Be ions. Thus, the electron running time is not increased and a hole is impressed with intensive field near the drain electrode (+) to be drifted while being impressed with very faint field near the source electrode (-) so that the hole may be arrested by a lattice defect led in the part near the source electrode only to decide the life time for improving the response. In such a constitution, the loss in current gain can be minimized while improving the response characteristics to manufacture a photodetector with high gain band width space.

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.

(Prior Art) Compound semiconductor light-receiving elements are used in optical receivers for optical communications or optical information processing, and efforts are being made to develop high-speed, highly sensitive elements. 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, so they are less affected by the CR time constant, and the carrier life and carrier travel are less affected by the CR time constant. By designing the element to shorten the time,
There is hope that high gain bandwidth product (high GB product) characteristics can be obtained.

In the 1.0-1.6 pm wavelength band, which corresponds to the low-loss band of optical fibers that are attracting attention for optical communications, InGaAs is the most suitable material for the light absorption layer of a semiconductor photodetector. An example of the basic structure of this InGaAs-based photoconductive semiconductor light receiving element is shown in FIG. This structure has an element structure in which an n-InGaAs layer 2 is crystal-grown on a semi-insulating InP substrate 1, and two electrodes 3 and 4 are formed on the surface of this semiconductor layer 2, which is further mesa-etched. . A voltage is applied between these two electrodes, and the conductivity increases due to photoexcited carriers incident between the two electrodes, thereby converting an optical signal into an electrical signal. Here, in the case of an n-type semiconductor, the internal current gain is G = -c/l (1)
°C: Hole lifetime t: Determined by electron transit time. In the case of transit time limitation, I is the transit time of holes, so the current gain is determined by the ratio of the transit times of holes and electrons. In III-V group semiconductors, electrons travel at a faster speed than holes, so the gain is always greater than 1. Furthermore, the response characteristics are limited by the slow transit time of the holes, which causes tailing of the pulse response. Therefore, in order to improve the response characteristics, attempts have been made to shorten the lifetime of holes by damaging the semiconductor and creating a level that traps holes. That-
An example is shown in FIG. In this example, after electrodes are formed in the same manner as in the example shown in Figure 2, Be++ ions are implanted at an acceleration energy of 400 keV to a depth of about 4 x 1010 cm-2 to create defects in the semiconductor (Applied Fixtures).
Letters (Appl, Phys, Lett,) 46
(4), pp396-398.1985).

(Problem to be solved by the invention) However, if there is a uniformly damaged region 6 in the semiconductor between the electrodes, the lifetime of holes becomes short, and at the same time the transit time of electrons becomes long due to deterioration of mobility. Therefore, in equation (1), the numerator becomes small and the denominator becomes large, so that the gain is suppressed to a small value. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve these conventional drawbacks and provide a high-speed response while minimizing gain loss. That is, the object is to provide a photoconductive semiconductor light-receiving element with a high GB product.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides a photoconductive semiconductor light-receiving element, which is a conductive type in which electrons and holes, whichever has a faster traveling speed, are majority carriers. on the semiconductor surface of
It has a pair of electrodes, and has a structure in which carriers travel in a direction parallel to the surface by an electric field applied between the electrodes, and a minority carrier trap level is created only in a specific region near the electrode on the side where minority carriers reach. It is characterized by the formation of

(Function) The present invention solves the problems of the prior art by adopting the above-described configuration. That is, in the photoconductive semiconductor light-receiving device according to the present invention, for example, if we take an example in which the faster-moving majority carriers are electrons, only the region near the source electrode in the n-type semiconductor (the region where holes exit the semiconductor) Since a trap level is formed at Minimized. At the same time, holes that have drifted to the vicinity of the source electrode are trapped by lattice defects introduced near the source instead of slowly leaving the electrode under a weak electric field, and their lifetime is determined, improving response. is obtained. This holds true even if the roles of electrons and holes are reversed.

In this way, high gain bandwidth product (high GB product) characteristics are achieved.

(Example) An example of the present invention will be described in detail below 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, n--InGaAs2 is formed on the semi-insulating InP substrate 1.
After crystal growth of ~1.5 pm, a source electrode 4 and a drain electrode 3 are formed by vacuum evaporation of AuGeNi and heat treatment. Next, mesa etching is performed to remove the InGa outside the light receiving area.
Remove As. Next, after forming a 5i02 film 5, a photoresist process is performed to form a 5i02 film 5 in a specific area near the source electrode.
02 is removed, and using this photoresist, 5i02, and a mask, Be+1 is ion-implanted into the selected region at an acceleration energy of 400 keV and a dose of I.times.10"cm@-2 to form a damaged region.

In the device obtained in this way, lattice defects that cause carrier mobility deterioration are introduced only in a limited area near the source electrode, so there is little effect of increasing electron transit time (denominator of equation (1)). .

In addition, holes are not generated by photoexcitation and immediately trapped, and the molecules that travel to the vicinity of the source electrode (molecules in formula (1)) do not become extremely small. Therefore, current loss can be minimized.

By the way, when considering a hole traveling between electrodes, it feels a strong electric field near the drain electrode (+ electrode) and drifts, but it feels a very weak electric field near the source electrode (- electrode), so it drifts at high speed. So I can't go out to the electrode. This limited the effective transit time of holes and was a cause of response deterioration (J, C).

Gammel doctoral dissertation, p122. (See Cornell University, 1980).

According to the present invention, instead of the holes traveling near the source electrode slowly exiting to the electrode under a weak electric field, they are trapped by lattice defects introduced only near the source, and their lifetime is determined. This improves the response and eliminates the tailing of the trailing edge of the pulse.

In the above embodiment, ion implantation is used to form the trap level, but the trap level may be formed by other methods such as impurity diffusion.

(Effects of the Invention) As explained above, according to the present invention, it is possible to minimize current gain loss, improve response characteristics, and provide a photoconductive material with high GB product characteristics. A semiconductor photodetector can be realized.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a cross-sectional structure of a photoconductive semiconductor light-receiving device showing an embodiment of the present invention, and FIGS. 2 and 3 are schematic diagrams of a cross-sectional structure of a photoconductive semiconductor light-receiving device showing conventional examples. . In the figure, 1: semi-insulating InP substrate, 2: n-1
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Claims (1)

[Claims] A pair of electrodes is provided on the surface of a conductive type semiconductor in which the faster traveling speed of electrons and holes is the majority carrier, and an electric field applied between the electrodes causes the carriers to travel in a direction parallel to the surface. A photoconductive semiconductor light receiving element characterized in that a minority carrier trap level is formed only in a region near an electrode on the side where minority carriers reach.