JPH0614559B2 - Integrated photoelectric conversion element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a photoelectric conversion element, particularly an integrated conversion element capable of generating a high voltage.

[Background technology]

When the photodiode is integrated in the semiconductor substrate as shown in FIG. 1, for example, a plurality of PN diodes as shown in FIG. 2 are formed by the conductive film 8 on the insulating film on the surface of the semiconductor substrate 4.
A method of connection as shown in FIGS. 2 and 3 is conceivable, but in this case, the Darlington connection of the bipolar transistor is used, and only a small output voltage / current can be obtained.

[Object of the Invention]

Therefore, an object of the present invention is to reduce leakage current due to a parasitic bipolar transistor and efficiently generate a high voltage.

[Disclosure of Invention]

To achieve the above object, the present invention provides a first-conductivity-type semiconductor substrate, a plurality of reverse-conductivity-type first regions formed separately on the substrate surface portion, and these reverse-conductivity-type first regions. A second region of the first conductivity type formed on the surface and one of the first regions provided on the insulating film formed on the surface of the semiconductor substrate are formed in another first region separated from them. Amplification factor β of a parasitic bipolar transistor including a first conductive type semiconductor substrate and a first conductive type second region and a first conductive type semiconductor region and a reverse conductive type first region, respectively. Satisfies the relation β << 1, the junction depth of the first region with the semiconductor substrate is x _j , the number of first regions connected to each other is n, and the absorption coefficient of incident light is α. When these are The gist of the integrated photoelectric conversion element is characterized in that the junction depth x _j is determined so as to satisfy the following relational expression.

Hereinafter, the present invention will be described in detail with reference to the drawings showing an embodiment thereof. FIG. 4 shows a cross section of an embodiment of the present invention. Reference numerals 1 and 1a are P-type first regions, and are formed on the surface portion of an N-type substrate 4 via N ⁺ isolation diffusion regions 5 and 5a. It is formed to be separated. 2, 2a are N-type regions formed on the surface of the first regions 1, 1a.
Reference numerals 3 and 3a are P-type high-concentration regions, which are provided near the bonding surfaces of the first regions 1 and 1a with the substrate.
Reference numerals 6 and 6a are P diffusion regions for the effect as a channel stopper and ohmic contact, and 7 is an insulating film formed on the surface of the substrate 4. Reference numeral 8 is a conductive thin film provided on the insulating film 7, and electrically connects the first region 1a and the second region 2 in the first region 1 formed apart from them.

FIG. 5 shows an equivalent circuit when n pieces of the photodiodes shown in the embodiment of FIG. 4 are connected in series. i _P1 is the photocurrent due to the emitter-base junction, i _P2 is the photocurrent due to the base-collector junction, i _B1 is the output current from the base, and i _E is the emitter current of the parasitic phototransistor. When the current amplification factor is β, the emitter current of the final stage (nth transistor T _rn ) is It is represented by. Here, i _E = β (i _p1 + i _p2 −i _B1 ). In order to generate the photocurrent i _B1 between both terminals A and K, it is necessary that i _En <i _B1 .

In order to increase the photocurrent i _B1 , it is necessary to reduce the leakage current amplified through the parasitic phototransistor. This means that β must be small. Although it is possible to reduce β by various methods, for example, as shown in FIG. 4, a first region having the same conductivity type as that of the first region is formed in the bonding region between the substrate 4 and the first regions 1 and 1a. This can be realized more easily by providing the regions 3 and 3a having a higher impurity concentration.

For example, by doing as in this embodiment, β <
If <1, the relationship of ni _E −i _P2 <i _B1 is obtained. Since i _B1 <i _p1 , i
The relationship between _p1 and i _p2 is (n-1) i _P2 <i _p1 (1). i _p1 and i _p2 are the incident light density Φ ₀ and the substrate of the first regions 1 and 1a. the junction depth of the 4 _{x j,} is expressed as the extinction coefficient of the incident light is _{α, i p2 = Φ 0 exp} (-αx j) i p1 = Φ 0 {1-exp (-αx j)} from the above equation (1) will be represented as (n-1) exp (-αx j) <1-exp (-αx j). Therefore, when β << 1, It becomes. That is, in order to generate a current between the A and K terminals, it is necessary that this relational expression (2) is satisfied.

For example, when x _j = 15 μm and 10 photo diodes are connected in series (n = 10), the red incident light λ
Since α = 2 × 10 ³ cm ⁻¹ for = 700 nm,
Substituting this into the right side of the above relational expression (2), the calculation is about 1
It becomes 2 μm, which satisfies the relational expression (2). That is, a desired photocurrent can be obtained.

The case where the conductivity types P and N of the embodiment are reversed is also included in the present invention.

〔The invention's effect〕

Since the integrated photoelectric conversion element according to the present invention is configured as described above, according to this, the photovoltaics having a high open circuit voltage boosted by the number of connected diodes from the diodes arranged in series on the monolithic substrate. Power is obtained.

[Brief description of drawings]

FIG. 1 is an explanatory view showing diodes connected in series, and FIG.
1 is a sectional view showing an integrated photoelectric conversion device realizing the diode series circuit of FIG. 1, FIG. 3 is an explanatory view showing an equivalent circuit of the device of FIG. 2, and FIG. 4 shows an embodiment of the present invention. FIG. 5 is a partial sectional view, and FIG. 5 is an explanatory diagram showing an equivalent circuit of the embodiment shown in FIG. 1,1a ... P-type first region, 2,2a ... N-type second region, 3,3a ... P-type high-concentration region, 7 ... insulating film,
8 ... Conductive film

Claims (2)

[Claims] 1. A first-conductivity-type semiconductor substrate, a plurality of opposite-conductivity-type first regions formed in the substrate surface portion at a distance from each other, and first and second opposite-conductivity-type first regions formed on the surfaces thereof. A second region of one conductivity type and one of the first regions provided on the insulating film formed on the surface of the semiconductor substrate, to a second region formed in the other first region separated from them. A current amplification factor β of a parasitic bipolar transistor, each of which is provided with a conductive film for electrical connection, and which includes a first region of opposite conductivity type and a second region of first conductivity type with respect to the first conductivity type semiconductor substrate.
Satisfies the relation β << 1, the junction depth of the first region with the semiconductor substrate is x _j , the number of first regions connected to each other is n, and the absorption coefficient of incident light is α. When these are An integrated photoelectric conversion element, wherein the junction depth x _j is determined so as to satisfy the following relational expression. 2. The high-concentration region of the opposite conductivity type having a higher impurity concentration than that of the first region is provided in the vicinity of the bonding surface with the semiconductor substrate in the first region. Integrated photoelectric conversion device.