JPH01122176A - Photo-diode - Google Patents

Abstract

PURPOSE:To eliminate free carrier absorption and photoelectric conversion loss due to the annihilation, etc., of electrons and holes generated by lowering the impurity concentration of another conductivity type layer to a proper value in relation to the position of a junction and spreading a depletion layer into the whole light-receiving region in an impurity introducing layer. CONSTITUTION:A p-type diffusion layer 21 and a high-concentration p<+> layer 22 which is connected to the p-type diffusion layer 21 and brought into ohmic- contact with an aluminum wiring 4 are formed to an n-type silicon substrate 1, and the surface is coated with a transparent insulating film 5. The p-type layer 21 is shaped in impurity concentration and depth where a depletion layer is formed extending over the whole light-receiving region. Consequently, the depletion layer 3 is shaped into the whole light-receiving surface region in the p-type layer 21 when a reverse bias is applied to a p-n junction between the n-type semiconductor element assembly 1 and the p-type layer 21. Accordingly, incident light is not absorbed to the p-type layer 21 before it reaches the depletion layer 3, thus minimally inhibiting free carrier absorption and photoelectric conversion loss due to the annihilation of electron-hole pairs.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a photovoltaic device that performs photoelectric conversion using a photocurrent generated by the incidence of light into a depletion layer created by applying a reverse bias to a p-n junction in a semiconductor element. Regarding diodes.

[Conventional technology]

Conventionally, this type of photodiode is shown in Figure 2 (Ml~
The structure shown in (0) is well known. (a) is a plan view of the photodiode, (bl and (C1) are respectively (a
) is a cross-sectional view taken along line c-c' and line DD'.

The figure shows a depletion layer 3 created by a p'-n junction formed by diffusing a highly doped p' layer 2 into an n-type silicon substrate 1. The p-swelling diffusion layer 2 has a high concentration of p+
The layers are usually MO3IC to reduce man-hours.
This is because it is formed using a shallow diffusion layer formation process such as the p channel source/drain formation process, and the reason why the shallow diffusion layer formation process is used is to introduce more light into the depletion layer. Aluminum arrangement 4 is p-
This is an electrode for applying a reverse bias to the n-junction and extracting photocurrent, and is in ohmic contact with the high concentration p' layer 2. A transparent insulating film 5 is coated on the upper surface.

The impurity concentration of the n-type silicon substrate 1 is set to 1.4×10IS/
-1 Impurity concentration of high temperature p layer 2 is 1.4 x 10"
/-, and when a 4 reverse bias voltage of 5V is applied between the two gate-shaped layers, a depletion layer 3 with a width dg-2, 4- is generated in the n-type silicon substrate 1. When light 6 enters here, electrons and
Hole pairs are generated and photocurrent flows.

[Problem that the invention seeks to solve]

However, this structure had the following problems. That is, in ta+ of FIG. 2, the area of the normally highly doped p'''[2 is much larger than the area of the depletion layer 3 exposed to the upper surface of the substrate 1, and a portion of the light absorbed by the highly doped p' layer 2 is is absorbed by free carriers and becomes heat, and does not become a photocurrent.The remaining light generates electron-hole pairs in the highly concentrated 99 layer 2, but some of them quickly disappear and form a depletion layer 3.
At even higher concentration 9, the photocurrent does not reach 9
If the junction depth of 0 layer 2 is 1-, especially at a wavelength of 500n-
The following short wavelength light is almost absorbed within the high concentration layer 2, and a loss of 0 or more significantly reduces the photoelectric conversion efficiency.

The object of the present invention is to eliminate the above-mentioned drawbacks and to
It is an object of the present invention to provide a photodiode which can reduce free carrier absorption of incident light including short wavelength light of nm or less to a minimum and make maximum effective use of generated electron-hole pairs as photocurrent.

[Means for solving problems]

In order to achieve the above object, the present invention applies a reverse bias to a p-n junction between a layer of another conductivity type formed on the light-receiving surface side of a semiconductor element of one conductivity type to create a depletion layer. generate,
In a photodiode that generates a photocurrent by the incidence of light into its depletion layer, the layer of the other conductivity type has an impurity concentration and depth such that a depletion layer is formed over the entire light-receiving region.

[Effect]

When a reverse bias is applied to the pn junction between the semiconductor element of one conductivity type and the layer of the other conductivity type, a depletion layer is generated over the entire light-receiving surface of the layer of the other conductivity type. It is not absorbed by conductive layers, and photoelectric conversion losses due to free carrier absorption and annihilation of electron-hole pairs are kept to a minimum.

Furthermore, the depletion layer capacity decreases and the electron/hole generation efficiency increases.

〔Example〕

Figure 1 (C1) shows an embodiment of the present invention with the same reference numerals attached to parts common to Figure 2, Figure (a) is a plan view of the photodiode, Figure (b), (0 ) are shown in Figure 1, respectively.
ml is a cross-sectional view taken along lines A-A'' and B-8'.

An n-type silicon substrate l with an impurity concentration ND/- has an impurity concentration NA/cd, a p-swelled diffusion layer 21 with a junction depth of 1n, and a high-concentration p layer for connecting to the p-type diffusion N21 and making ohmic contact with the aluminum wiring 4. ""Ji22 is formed. Second
As in the figure, the surface is covered with a transparent insulating film 5.

Impurity concentration N(3-'') in the step junction approximation.

Depletion layer width x4 when a reverse bias (V) is applied between an N-type semiconductor and a P-type semiconductor of Na (cm-”)
(1) is expressed as. However, 6s is the relative dielectric constant of St, which is 12°6
o is the dielectric constant of vacuum, 8.85 x 10-th F/am,
q is the electron charge and is 1.6 XIO”C.V41
is the diffusion potential and is expressed by the following formula.

However, k is the Boltzmann constant, T is the absolute temperature + ni is the intrinsic carrier density. Here ND-1,4X10”
/-, and when the concentration NA of the p-swell diffusion layer 21 is changed when a reverse bias of 5 .mu. is applied, the depletion layer width X becomes as shown in Table 1.

Table 1, Figure 3 illustrates Table 1. Therefore, x, −
A depletion layer with a width dt of 1/2 of 3.3tna and a depth of 1.7- is generated, and the entire pi21 with a depth of 1- becomes a depletion layer.

However, only the area around the high concentration 20 layer 22 is as shown in Figure 1 (al,
As shown in +1lt), a depletion layer with a width d and -2.4μ is generated on the substrate 1 side. When light 6 is incident on this photodiode, the entire light receiving region from the surface to a depth of 2.7 nm is a depletion layer, so there is a photoelectric conversion loss due to light absorption in the conductive layer, that is, free carrier absorption and the generated electron/genuine plate pair. Disappearance does not occur on the surface, but only occurs within the substrate 1 for long wavelength light that penetrates 2.7- or more. Furthermore, since the depletion layer capacitance decreases due to the increase in the depletion layer, the photocurrent generation efficiency increases, resulting in a significant improvement in sensitivity compared to the case shown in FIG. Although the depth of the second layer 21 is the same as in the case of FIG. 2, the impurity concentration can be increased by making it shallower.

FIG. 4 shows another embodiment of the photodiode, which has a structure in which a p-swelled diffusion layer 23 is embedded in an n-type silicon substrate 1, in which the p-n junction is not exposed on the surface, and the surface leakage current is small. There are advantages. In this embodiment as well, by adjusting the impurity concentration and junction position of the p-type diffusion M23, the upper part of the p-swelling diffusion layer 23 up to the surface of the substrate 1 and the p-swelling diffusion layer 23 itself are all made into the depletion layer 3. It becomes clear that the same effect can be obtained upon incidence of light 6. The second layer 23 is drawn out to the surface at a portion not shown and connected to wiring.

〔Effect of the invention〕

According to the present invention, the impurity concentration of the other conductivity type layer of a photodiode using a p-n junction between a substrate of one conductivity type and a layer of another conductivity type is reduced to an appropriate value in relation to the junction position. Since the depletion layer is made to spread over the entire light-receiving region of the impurity-introduced layer, the incident light reaches the depletion layer without being absorbed by the other conductivity type layer, and the free carrier absorption and the generated electrons and Photoelectric conversion loss due to disappearance of holes is almost eliminated. Furthermore, since the depletion layer width becomes larger, the depletion layer capacitance decreases and the electron/hole pair generation efficiency increases. This results in
A photodiode with improved sensitivity including sensitivity to short wavelength light can be obtained.

[Brief explanation of the drawing]

A of FIG.
1 (C) is a sectional view taken along the B-8' line of Ta), Figure 2 +a+, (bl, (C) is a conventional photodiode, and similarly ta) is Plan view, (b)
is a sectional view taken along the c-c' line of (al), (C) is D of Ta)
-El'l arrow sectional view, Figure 3 is a relationship between the impurity concentration of the p-layer forming a p-n junction and the depletion layer width when the impurity concentration of the n-layer is constant, and Figure 4 is a diagram of the present invention. FIG. 3 is a cross-sectional view of another embodiment of the invention. 1: n-type silicon substrate, 21. 23: p diffusion layer, 22
: High concentration p-layer layer, 4: Wiring. Figure 1

Claims (1)

[Claims] 1) A depletion layer is created by applying a reverse bias to the p-n junction between a semiconductor element of one conductivity type and a layer of another conductivity type formed on the light-receiving surface side of the element. A photodiode in which a layer of another conductivity type has an impurity concentration and depth such that a depletion layer is generated over the entire light-receiving region, in which a photocurrent is generated by the incidence of light into the depletion layer. . 2) In the diode according to claim 1,
A photodiode characterized in that a layer of another conductivity type and a layer of one conductivity type have approximately the same impurity concentration.