JPH0456174A - Photoconductive type 4-quadrant light-detection element - Google Patents

Abstract

PURPOSE:To enable a dead zone of a light-receiving part to be reduced and enable sensitivity to be uniform and crosstalk to be reduced by dividing the light-receiving part into four regions with a thin common electrode and a thin groove reaching a substrate which crosses it at right angle and by placing four independent electrodes at each divided region. CONSTITUTION:A light-receiving part is divided into four regions by a thin common electrode 3' and a thin groove 5 which crosses it at right angle and other electrode 3 is provided in parallel to the electrode 3' at each divided region, thus enabling the light-receiving part to be divided at the thin electrode 3' or the groove 5 and a dead zone to be reduced. Also, since bias current flows in parallel between the electrode 3' and other electrode 3 within the light-receiving surface, bias current intensity distribution becomes uniform and sensitivity becomes uniform. Also, when the electrode 3' is set to a higher potential side for the independent electrode, sensitivity near the electrode 3' can be further improved. Further, since the light-receiving part is divided into the thin electrode 3' and the groove 5, electrical and optical independence of light-detection elements at each quadrant can be increased and crosstalk can be reduced. Then, bias current flows in parallel between the electrode 3' and other electrode 3 within the light-receiving surface, thus enabling bias current intensity distribution to be uniform and sensitivity to be uniform.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a photodetection element, particularly a photoconductive four-quadrant photodetection element.

[Conventional technology]

FIG. 4 is a diagram showing the structure of a conventional photoconductive four-quadrant photodetecting element, in which (a) is a plan view thereof, and (b) is a view in the direction of the TVb arrow in FIG. 31. , 1 is a high-resistance substrate, 2 is a compound semiconductor, 3 is an electrode, and 4 is a submount.

Next, the operation will be explained. FIG. 4 shows a conventional four-quadrant photodetecting element in which four photoconductive type photodetecting elements are arranged between a pair of opposing electrodes and a region of a sandwiched compound semiconductor 2 serves as a light receiving part. A photoconductive type photodetecting element is constructed by passing a constant bias current i between a pair of electrodes, and
This is a photodetecting element that utilizes the fact that when the resistance value between the electrodes changes (decreases) due to carriers generated by absorbing incident light within the sensor, this appears as a potential fluctuation between the electrodes. A four-quadrant detection element is basically composed of four photodetection elements, and is an element for detecting the position of the incident signal light based on the amount of incidence on each photodetection element, that is, the magnitude of the output signal. be.

However, in the configuration example shown in FIG. 4, the central electrode portion is a dead zone that does not sense incident light, and this occupies a large area, making it impractical.

That is, in a four-quadrant light detection element, it is important to minimize the proportion of incident light that is blocked by the electrode in the light-receiving region, and an example of a configuration with a small insensitive body head is shown in FIG. .

That is, FIG. 5(a) is a plan view showing another example of a conventional photoconductive type four-quadrant photodetecting element, and FIG.
It is a view taken along the arrow b, and in the figure, the same reference numerals as in FIG. 4 indicate the same or corresponding parts, and 3v is a common electrode.

The four-quadrant photodetecting element shown in Fig. 5 is monolithic and easier to manufacture than the element shown in Fig. 4. In addition, the light-receiving part is divided into a narrow cross-shaped common electrode 3" in the center.
The feature is that the dead zone area is small.

[Problem to be solved by the invention]

However, since the conventional four-quadrant photodetecting element shown in FIG. 5 was constructed as described above, in FIG. Considering the intensity distribution of the bias current iB flowing between the electrodes, it is weakest at the center of the cross, then stronger at the periphery of the cross, and strongest around the electrodes at the four corners.

Furthermore, since the sensitivity of the element is proportional to the applied electric field strength, that is, the bias current strength, the bias current strength distribution also corresponds to the sensitivity distribution. Therefore, the bias current unevenness mentioned above also leads to sensitivity unevenness, and in the conventional four-quadrant photodetecting element shown in FIG. 5, the sensitivity is the lowest in the central portion of the most important light receiving section (this was a problem).

Furthermore, the central cross-shaped common electrode section becomes a dead zone that does not sense light, so it must be made as thin as possible, but on the other hand, if it is made thin, signal interference (crosstalk) will occur between adjacent photodetecting elements. This had an optical cause and an electrical cause due to an increase in electrical coupling due to an increase in electrode resistance.

As described above, with the element having the structure shown in Figure 5, it is possible to reduce the dead zone in the light receiving section, but there are problems such as sensitivity unevenness and crosstalk within the light receiving surface, which still need improvement. Met.

This invention was made to solve the above-mentioned problems, and is a photoconductive four-quadrant light detection system that can reduce the dead zone area of the light receiving section, equalize sensitivity, and reduce crosstalk. The purpose is to obtain an element.

[Means to solve the problem]

In the photoconductive four-quadrant photodetecting element according to the present invention, the light-receiving part is divided into four by a thin common electrode and a narrow groove extending to the substrate perpendicular to the common electrode, and each of the four divided areas has another four areas parallel to the common electrode. Two independent electrodes are arranged.

Further, in such a structure, the potential of the common electrode is set to a higher potential side than the independent electrode.

Further, the photoconductive four-quadrant photodetecting element according to the present invention divides the light receiving part into four with a thin cross-shaped common electrode, and each of the four divided areas is in contact with the common electrode,
A thin groove reaching the substrate is formed, and four other independent electrodes are arranged at right angles to each groove.

[Effect]

In the photoconductive four-quadrant photodetecting element of the present invention, the light-receiving area is divided into four by a thin common electrode and a thin groove perpendicular to the common electrode, and another electrode is provided in each divided area in parallel with the common electrode. The light-receiving section is divided into thin common electrodes or grooves, resulting in: 1. The dead zone becomes smaller. Further, since the bias current flows in parallel between the common electrode and other electrodes within the light receiving surface, the bias current intensity distribution is made uniform, and the sensitivity is also made uniform.

Further, in the case where the common electrode is set to a higher potential side than the independent electrodes, the sensitivity near the common electrode is further improved.

In addition, the light receiving section is divided into four parts by a thin cross-shaped common electrode, and a groove is formed in each divided area to contact the common electrode.
Furthermore, since other electrodes are placed at right angles to each groove, the light-receiving area is divided by the thin common electrode and the groove, making it possible to increase the electrical and optical independence of the photodetecting elements in each quadrant. This reduces crosstalk. Furthermore, since the bias current flows in parallel between the common electrode and the other electrodes within the light-receiving surface, the bias current intensity distribution is made uniform, and the sensitivity is also made uniform.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a photoconductive four-quadrant photodetector according to an embodiment of the present invention, and FIG. 1(a) is a plan view thereof, and FIG.
B) and (C) are the Ib arrow view and IC arrow view of Figure (a), respectively, where ■ is a high-resistance substrate, 2 is a compound semiconductor layer, 3 is an electrode (independent electrode), 3゛ is a common electrode,
5 is a thin groove.

The common electrode 3'' shown in FIG. 1 has the same function as the conventional common electrode 3° shown in FIG. 5, except that in this embodiment it has a linear shape instead of a cross shape.

In addition, a thin groove 5 is provided at right angles to the common electrode 3°, passing through the compound semiconductor 2 and reaching the high-resistance substrate 1 to divide the light receiving section, and a linear groove parallel to the common electrode 3° is also provided. An independent electrode 3 is provided for each photodetector element.

In such a configuration, the light receiving part is connected to the thin common electrode 3° and the groove 5.
Since it is divided by , the dead zone of the light receiving section can be made small, and furthermore, the intensity distribution of the bias current iB flowing between the common electrode 3'' and the electrodes 3 in each quadrant parallel thereto becomes uniform throughout the light receiving section. Therefore, the sensitivity of the photodetector elements in each quadrant can be made uniform.

In addition, in the embodiment shown in FIG. 1, the voltage applied to cause the bias current to flow was not particularly described, but the common electrode 3' in FIG. 1 was set to a higher potential side than the other electrodes 3. It is also within the scope of embodiments of this invention. This will be explained below.

FIGS. 3(a) and 3(b) are diagrams for explaining the operation of a photoconductive four-quadrant photodetecting element according to an embodiment of the present invention.
is the signal light intensity distribution, and function) is the generated excess carrier concentration distribution.

In these figures, 2 represents a compound semiconductor, 3° represents a common electrode, 6 represents an incident light intensity distribution, and 7.7' and 71' represent an excess carrier concentration distribution.

Next, the operation will be explained.

Figure 3(a) shows the signal light incident on the common electrode at around 3°, where 2 is a compound semiconductor, 3'' is the common electrode, and 6 is the intensity distribution of the incident signal light. Of the signal light 6, only the shaded portion is the compound semiconductor 2.
is absorbed and becomes a valid signal. 3) shows the distribution of excess carriers generated in the compound semiconductor 2 by absorbing the signal light 6, and 7 represents the generated distribution, that is, the signal light distribution.

7' and 71' represent actual distribution maps of excess carriers taking into account carrier diffusion, drift, and recombination,
7' indicates the case where the common electrode 3° is on the low potential side (ie, the negative side) compared to the other electrodes 3, and 71' indicates the case where the common electrode 3° is on the high potential side (ie, the positive side). Since the compound semiconductor 2 used in the photoconductive type photodetecting element is usually an N-type semiconductor,
The excess carrier density is determined by the density of holes, which are minority carriers. On the other hand, among the pairs of holes, the electrons generated in the compound semiconductor 2 by absorbing the incident signal light are transferred from the common electrode 31 when the hole has a positive charge depending on the polarity of the common electrode 3g. Drift away. In addition, excess carriers of holes and electrons are removed from the common electrode 3"
The distribution of excess carriers is 7' when the polarity of the common IIT 3° is negative and 7'' when it is positive. By the way, the sensitivity of the photodetecting element is proportional to the number of excess carriers. Therefore, as is clear from FIG. 3(b), the sensitivity around the common electrode 3° in the center of the four-quadrant detection element can be prevented from decreasing by setting the common electrode 3° to the positive side.

Further, other embodiments of the present invention will be described with reference to the drawings.

FIG. 2(a) is a plan view of a photoconductive four-quadrant detection element according to another embodiment of the present invention, and FIG. 2(b) is a plan view of Ib of FIG.
A view in the direction of the arrows, (C) is a view in the direction of the Ic arrows in Figure a1.

In the figure, 1 is a high-resistance substrate, 2 is a compound semiconductor,
3 and 3'' are electrodes, and 5 is a thin groove.

The common electrode 3° shown in FIG. 2 is the same as the conventional one shown in FIG. The difference is that the photodetectors in the quadrants are provided.In this embodiment as well, the common electrode 3° and the other electrodes 3 are provided in a parallel positional relationship with each other, so the , the bias current is made uniform, and as in the embodiment shown in FIG. 1, the element sensitivity can be made uniform.

In addition, in this embodiment, a thin groove 5 is provided in contact with the cross-shaped common electrode 3'' as shown in FIG. In other words, the independence of each photodetection element is increased, and crosstalk can be reduced to the same level as the conventional four-quadrant photodetection element shown in FIG.

〔Effect of the invention〕

As described above, according to the present invention, a linear thin common electrode and a thin groove are provided at right angles to each other in the center of the light receiving section, and furthermore, the electrodes of each photodetecting element are arranged parallel to the common electrode. This has the effect of reducing the in-plane dead zone area, making the bias current uniform, and improving the uniformity of sensitivity. Furthermore, in such a configuration, since the potential of the linear common electrode at the center of the light receiving section is set to a higher potential side than the other electrodes, there is an effect that the sensitivity near the common electrode can be improved.

In addition, a groove is provided in contact with the cross-shaped common electrode at the center of the light-receiving section, and other electrodes are placed at right angles to the groove, which reduces the dead zone area within the light-receiving surface, equalizes the bias current, and improves sensitivity. This has the effect of improving uniformity and further reducing crosstalk between each photodetecting element.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a photoconductive type four-quadrant photodetecting element according to one embodiment of the present invention, FIG. 2 is a diagram showing a photoconductive type four-quadrant photodetecting element according to another embodiment of the present invention, and FIG. is a diagram showing the operation of a photoconductive type four-quadrant photodetecting element according to yet another embodiment of the present invention, FIG. 4 is a diagram showing a conventional photoconductive type four-quadrant photodetecting element, and FIG. FIG. 2 is a diagram showing a conventional photoconductive four-quadrant photodetecting element. In the figure, 1 is a high-resistance substrate, 2 is a compound semiconductor layer,
Reference numeral 3 indicates an electrode (independent electrode), 3" indicates a common electrode, 5 indicates a groove, and 7 indicates distribution of excess carriers. Note that the same reference numerals in the drawings indicate the same or corresponding parts.

Claims (3)

[Claims] (1) A photoconductive four-quadrant photodetecting element comprising a high-resistance substrate, a compound semiconductor layer formed on the substrate, and an electrode formed on the compound semiconductor layer, the surface of the compound semiconductor layer being a common electrode arranged linearly in the center of the light receiving section; and a groove reaching at least the substrate, arranged at right angles to the common electrode at the center of each light receiving section divided into two by the common electrode. . A photoconductive four-quadrant photodetecting element, characterized in that each light receiving section divided into four by the common electrode and the groove is provided with four independent electrodes arranged in parallel to the common electrode. (2) The photoconductive type 4 according to claim 1, wherein the potential of the common electrode is higher than that of the independent electrode.
Quadrant light detection element. (3) A photoconductive four-quadrant photodetecting element comprising a high-resistance substrate, a compound semiconductor layer formed on the substrate, and an electrode formed on the compound semiconductor layer, the surface of the compound semiconductor layer being a common electrode disposed in the center of the light receiving section in a cross shape so as to divide the light receiving section into four; and at least one common electrode disposed in each region of the four divided light receiving section so as to be in contact with the common electrode. A photoconductive four-quadrant photodetecting element comprising: a groove reaching the substrate; and four independent electrodes arranged perpendicularly to the groove in each of the four-divided areas of the light-receiving section. .