JPS61113287A - Photodetecting element - Google Patents

Abstract

PURPOSE:To improve the spectral sensitivity characteristics of a photo detecting element, by forming the defect region in the inner part of a substrate and the non-defect region near the surface of the substrate and by forming the P-N junction in the non-defect region whose thickness is suitable adjusted to shorten the life time of the carrier. CONSTITUTION:The defect region 3 containing a lot of fine defects and the non-defect region 4 containing no defects are formed in the N-type layer 2 formed near the surface of a P-type Si substrate 1. The life time of the carrier is so short in the defect layer 3 that the sensitivity to the infrared ray can be decreased in the deep region of the substrare. Combination of this photodiode and the cut off filter of infrared ray is able to remarkably decrease the sensitivity in the infrared region. As the vicinity of the P-N junction of this photodiode is the non-defect region, the leak current is reduced. The photodiode or phototransistor having various spectral sensitivity can be obtained by varying the position of the boundary between the defect region and the non-defect region and the depth of the P-N junction.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a photodetector element such as a photodiode or phototransistor that has improved spectral sensitivity.

<Prior art> Conventionally, photodetecting elements such as photodiodes and phototransistors have been used for exposure metering in cameras, but it is desirable for these to be sensitive only to the visible light range, so a filter that cuts infrared rays is used. was installed in the light receiving section.
However, conventional cut filters were unable to completely block infrared light.

<Problems to be Solved by the Invention> In order to reduce the sensitivity in the infrared region of a photodetector element such as the photodiode or phototransistor, the carrier lifetime τ of the substrate can be reduced. As the lifetime τ becomes smaller, the diffusion length = ■ becomes smaller, so the area that can contribute to the photocurrent of the substrate (area A of the photodiode shown in FIG. 2) becomes smaller.

FIG. 3 shows the relationship between the depth and the amount of light when incident light is absorbed by the S1 photodiode. When the sum of the depth Xj at the PNN junction and the depth of the region A is 30 μm, according to FIG. ) contributes about 86% to the photocurrent, and light (C) with an incident light wavelength of 8 Q Onm contributes about 69% to the photocurrent. Therefore, as shown in Figure 3, since long wavelength light enters the substrate more deeply, sensitivity to long wavelength light can be reduced by reducing the lifetime τ of carriers within the substrate. I understand.

Next, in order to reduce the lifetime τ of carriers in the substrate, it is necessary to reduce the specific resistance of the substrate, or to reduce the carrier lifetime τ in the substrate.
It is possible to introduce a lifetime killer such as

However, the former has the disadvantage of a decrease in breakdown voltage and a delay in response speed due to an increase in capacity, while the latter has the disadvantage of an increase in leakage current.The present invention has been made in view of the above points, It is an object of the present invention to improve the spectral sensitivity characteristics of a photodetecting element by reducing the lifetime without causing the above-mentioned drawbacks.

<Example> Hereinafter, an example of the photodetecting element according to the present invention will be described in detail.

FIG. 1(a) shows a side sectional view of an embodiment of a photodetecting element according to the present invention. 1 is a 5iOP type substrate, and 2 is an N type layer formed near the surface thereof. 3 is a defective region having a large number of microdefects, and 4 is a defect-free region having no defects. Intrinsic φ gettering technology is used to form the defective region 3 and defect-free region 4. In this technique, heat treatment causes oxygen precipitation in Si, which becomes a nucleus and creates micro defects. The above oxygen precipitation nucleus is 500~
Generated by heat treatment at about 900℃, then 1000℃
If a certain degree of heat treatment is performed, the oxygen precipitation nuclei will become micro defects. In the vicinity of the substrate surface, a defect-free layer is formed by outward diffusion of oxygen during the latter heat treatment. The width of this defect-free layer depends on the high temperature heat treatment time and the initial oxygen concentration of the substrate. That is, the shorter the high-temperature heat treatment time and the higher the initial oxygen concentration, the narrower the width of the defect-free layer becomes.

In the photodetecting element formed as described above, the defect layer 3
In this case, the lifetime of carriers is significantly shortened, so the sensitivity of infrared light that enters deep into the substrate can be reduced. FIG. 1 et al.) show the characteristics of the spectral sensitivity of the conventional photodiode (curve 5) and the spectral sensitivity of the photodiode according to the present invention (curve 6). As shown in the figure, the spectral sensitivity of the photodiode according to the present invention is decreased in the infrared region.

Therefore, by combining this photodiode and an infrared cut filter, the sensitivity in the infrared region can be greatly reduced. Furthermore, in this photodiode, PN
The position of the boundary between the defect area 3 and the defect-free area 4 and the depth of the PN junction are changed in the photodetecting element according to the present invention, which has the advantage of reducing leakage current because the vicinity of the junction is a defect-free area. By doing so, photodiodes or phototransistors with various spectral sensitivities can be obtained.

Effect> According to the present invention, the spectral sensitivity characteristics of the photodetecting element can be improved.

[Brief explanation of the drawing]

FIG. 1(a) is a side sectional view of an embodiment of the photodetecting element according to the present invention, FIG. 1(b) is a characteristic graph thereof, and in FIG.
l: P type substrate 2: N type layer 3: defect area 4:
Defect-free area agent Patent attorney Yoshihiko Fuku (and 2 others) χ (nm) Figure 2 - m) Figure 3

Claims (1)

[Claims] 1. Form a defect-free region inside the substrate and a defect-free region on the surface of the substrate, form a PN junction in the defect-free region, and adjust the thickness of the defect-free region appropriately to obtain appropriate spectral sensitivity characteristics. A photodetecting element characterized by: