JPH0482269A - Two-dimensional array photodetector - Google Patents

Abstract

PURPOSE:To reduce a crosstalk without lowering an aperture rate by a method wherein a microlens is formed on a substrate on the side of an incident face in such a way that it corresponds to each photoelectric conversion part. CONSTITUTION:A substrate 1 is etched to be a concave shape. After that, a layer which is transparent with reference to incident light and whose refractive index is larger than that of the substrate 1 is formed on it. Then, its surface is polished to be a plane shape; a microlens is formed on the incident face of the substrate 1 on the same axis as each photoelectric conversion part 3. By this constitution, the incident light on the lens 8 is narrowed to a small spot and is incident on the photoelectric conversion part 3; and the outer shape of each microlens 8 becomes a photodetection part 4. As a result, the photoelectric conversion part 3 of the photodetection part 4 can be made small. Consequently, an interval between adjacent photoelectric conversion parts can be made larger than the diffusion distance of carriers from both sides, and a crosstalk between picture elements can be reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a back-illuminated photodetector having an array of photoelectrically convertible light-receiving sections, and in particular to a back-illuminated photodetector that can reduce crosstalk and improve the aperture ratio. This invention relates to a two-dimensional array photodetector.

[Conventional technology]

3 and 4 are a sectional view showing the structure of a conventional two-dimensional playback photodetector and a plan view showing the arrangement of a photoelectric conversion section.

In these figures, 1 is a high-resistance substrate, 2 is a compound semiconductor layer, 3 is a photoelectric conversion section, 4 is a light receiving section, 5 and 5' are electrodes for extracting electrical signals, and 6 is an optical filter.

Next, the operation will be explained.

FIG. 3 shows an example in which the photoelectric conversion section 3 is a photodiode formed by a PN junction formed on the compound semiconductor 2. In FIG. Therefore, as shown in FIG. 4, the light receiving section 4 forms a concentric circle with a radius increased by the carrier diffusion length on the outside of the photoelectric conversion section 3. Therefore, in order to reduce crosstalk between adjacent pixels, it is necessary to make the interval between the light receiving parts of each pixel as large as possible so that at least the light receiving parts do not overlap. On the other hand, the area ratio of the light receiving part within the light receiving surface (
It is not a good idea to widen the pixel pitch in order to increase the aperture ratio (aperture ratio); therefore, conventional two-dimensional array photodetectors are arranged so that the light-receiving areas of adjacent pixels are in contact with each other, as shown in Figure 4. Ta.

Since the electrodes 5 and 5° are formed on the surface of the compound semiconductor 2, the incident light is normally made to enter from the substrate 1 side, that is, the back surface, and an optical filter is provided on the incident side to remove unnecessary light components. I had set 6.

[Problem to be solved by the invention]

Since the conventional two-dimensional array photodetector was constructed as described above, it was easy to cause cross distortion as described below, and an improvement was required.

In the conventional two-dimensional array photodetector shown in Figure 4, due to the aperture ratio, the light-receiving areas of each pixel are arranged in a lattice shape so that they touch each other, so carriers generated at the boundaries are stochastically The current would be divided vertically or horizontally, and the occurrence of crosstalk was unavoidable.

Further, as shown in FIG. 3, there is a problem in that the reflected light 7 from the optical filter 6 enters other pixels, causing crosstalk.

This invention was made to solve the above-mentioned problems. It reduces crosstalk without lowering the aperture ratio, eliminates the need for an optical filter, and eliminates crosstalk caused by reflected light. The purpose of this study is to obtain a high-performance two-dimensional array photodetector.

[Means to solve the problem]

The two-dimensional array photodetector according to the present invention has microlenses formed on a substrate on the entrance surface side corresponding to each photoelectric conversion section.

Furthermore, in a second invention, the above-mentioned microlens is formed of a compound semiconductor having a different composition ratio to have a function equivalent to an optical filter.

Furthermore, in a third aspect of the invention, the photoelectric conversion sections are arranged so that six pixels are in contact with each other in a regular hexagonal shape around one pixel.

[Effect]

The two-dimensional array photodetector according to the present invention converts incident light into a small spot using a microlens formed on a substrate, and makes the spot enter a photoelectric conversion section.

Furthermore, by forming the microlenses from compound semiconductors with different composition ratios, it is possible to provide them with a function equivalent to that of an optical filter.

Further, by arranging the photoelectric conversion parts so as to be in contact with each other in a regular hexagonal shape, the aperture ratio can be improved.

〔Example〕

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

FIG. 1 shows a two-dimensional array photodetector according to an embodiment of the present invention, and in the figure, 8 is a microlens formed on the entrance side of the substrate 1. In FIG.

FIG. 2 shows an example in which photoelectric conversion units are arranged so that six pixels are in contact with one pixel in a regular hexagonal shape.

Next, the operation will be explained.

In FIG. 1, the microlens 8 is formed on the entrance surface of the substrate 1 on the same axis as each photoelectric conversion section 3. As shown in FIG. This microlens is formed by etching the substrate 1 into a concave shape, forming a layer thereon that is transparent to incident light and having a higher refractive index than the substrate 1, and then polishing the surface into a flat surface. can. Therefore, the light incident on the microlens 8 is focused into a small spot and is incident on the photoelectric conversion unit 3. That is, the outer shape of each microlens becomes the light receiving section 4 shown in FIG. Therefore, if the light receiving section 4 is the same size as the conventional one, the photoelectric conversion section 3 can be made smaller than before, and as a result, the distance between adjacent photoelectric conversion sections can be made larger than the diffusion distance of carriers from both. Crosstalk between pixels can be significantly reduced.

In addition, as a material for the microlens 8, a compound semiconductor 2
By changing the composition and using a filter with a different absorption wavelength band, it is possible to provide the same function as a conventional optical filter. This microlens 8 is processed with higher precision than an optical filter, and its parallelism with the light receiving section 4 is sufficiently good, so crosstalk caused by unnecessary reflected light can be significantly reduced compared to the case of conventional optical filters. . Note that in this case, the reflection intensity at the interface between the microlens 8 and the substrate 1 is weak, so there is no problem.

FIG. 2 shows the planar arrangement of a two-dimensional array photodetector in which pixels are arranged so that one light receiving section 4 is surrounded by six other light receiving sections in contact with each other in a regular hexagonal shape. In this example, the light receiving section is Unnecessary gaps between the parts 4 are reduced, and the aperture ratio is improved from 79% to 91%.

〔Effect of the invention〕

As described above, according to the present invention, microlenses are formed on the substrate on the entrance surface side corresponding to each photoelectric conversion section, so that
The photoelectric conversion section can be made relatively small, which has the effect of reducing crosstalk.

Furthermore, according to the second invention, since the above-mentioned microlens is formed of a compound semiconductor with a different composition, it can be provided with a function equivalent to an optical filter, and by eliminating the conventional optical filter, reflected light can be reduced. This has the effect of reducing crosstalk due to

Furthermore, according to the third invention, since the light receiving parts are arranged so as to be in contact with each other in a regular hexagonal shape, there is an effect that the aperture ratio can be improved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a two-dimensional array photodetector according to an embodiment of the present invention, FIG. 2 is a sectional view showing a two-dimensional array photodetector according to a second embodiment of the invention, and FIG. Fourth
The figures are a sectional view and a plan view showing a conventional two-dimensional array photodetector. In the figure, 1 is a substrate, 2 is a compound semiconductor, 3 is a photoelectric conversion section, 4 is a light receiving section, and 8 is a microlens. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (3)

[Claims] (1) In a two-dimensional array photodetector consisting of a high-resistance substrate, a compound semiconductor formed on the substrate, and a plurality of photoelectric conversion sections arranged in a two-dimensional array on the compound semiconductor, in addition to the substrate, A two-dimensional array photodetector characterized in that microlenses are formed on a surface of a transparent material having a refractive index larger than that of a substrate. (2) The two-dimensional array according to item 1, characterized in that a compound semiconductor having a composition ratio different from that of the compound semiconductor constituting the photoelectric conversion section is used as the material of the microlens, and has a function equivalent to an optical filter. Photodetector. (3) The two-dimensional array photodetector according to item 1, wherein the photoelectric conversion units are arranged in such a manner that six pixels are arranged around one pixel in a regular hexagonal shape.