JPH088075B2 - Photoelectric conversion device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a photoelectric conversion device for converting light into an electric signal, and particularly to a photoelectric conversion device that realizes high sensitivity by using a charge multiplication effect in an amorphous semiconductor. Regarding the converter.

[Prior Art] Conventionally, as a photoelectric conversion element mainly composed of an amorphous semiconductor, a photocell, a one-dimensional image sensor (for example, Japanese Patent No. 1022633), a solid-state driving circuit and an amorphous photoconductor are combined. Two-dimensional image sensor (for example, Japanese Patent Publication Sho-59-26)
154), a photoconductive image pickup tube (for example, Japanese Patent No. 902189).
Are known. In these photoelectric conversion elements, one having a blocking type structure having a junction characteristic that blocks the injection of charges from the signal electrode to the photoconductive film, and one or both electrodes having charges injected There is a structure that employs a so-called injection type structure.

In the injection type element, in principle, more electrons than the number of incident photons can be taken out to an external circuit, so that it is possible to increase the sensitivity to a gain higher than 1, and for the purpose of increasing the sensitivity of the photoelectric conversion element, For example, an image pickup device in which a photoconductive film having a phototransistor characteristic and a reading circuit are laminated (Japanese Patent Laid-Open No. 61-
222383) has been proposed.

For the same purpose, as an element in which the photoelectric conversion section itself has a multiplication effect, an electrostatic induction type transistor (IE EE Transaction on Electron Devices 1975, EI Day 22, pp. 185-197, IEEE TRAN
SACTION ON ELECTRON DEVICES, ED22) has been proposed, or it is an amorphous semiconductor mainly composed of Si containing hydrogen and halogen (eg, fluorine, chlorine, etc.), and p ⁺ similar to crystalline Si. A method of forming a πpnn ⁺ junction and generating an avalanche operation in the depletion layer of the pn junction to perform signal amplification (Japanese Patent Application No. 55-95953) has also been proposed. On the other hand, when the blocking junction structure having the property of blocking the inflow of charges from the outside of the photoconductive film is adopted, only the part of the incident light converted into the charges inside the photoconductive film becomes the signal current, so that The conversion gain is usually limited to 1 or less. However, recently, if a method of forming a blocking junction structure with an amorphous semiconductor mainly composed of Se and generating an avalanche operation in the amorphous semiconductor layer to perform signal amplification is adopted, an element with a blocking junction structure is obtained. However, it has been proposed by the inventors of the present patent that the photoelectric conversion efficiency can be made larger than 1. (Television Technical Report
1987, Vol. 10, pp. 1 to 6) [Problems to be solved by the invention] Regarding photoelectric conversion devices such as photocells, one-dimensional image sensors, photoconductive film laminated solid-state light receiving elements, etc. If adopted, in principle, more electrons than the number of incident photons can be taken out to the external circuit, so that it is possible to increase the sensitivity to a gain higher than 1, but in this way a part of the charge is injected into the sensor. However, this method is not preferable because the light response characteristics are significantly deteriorated. Further, since the static induction transistor has a system in which an amplification unit is built in for each pixel, it is difficult to make the amplification factors of the pixels equal to each other.

On the other hand, in an example using an amorphous semiconductor, a uniform film can be formed at a relatively low temperature, and since the film resistance is high, a complicated pixel separation process such as crystalline Si is not required, and a high resolution is achieved. There is an advantage that can be realized. However, some problems still remain in the light-receiving element that has been conventionally proposed to which the avalanche multiplication phenomenon in an amorphous semiconductor is applied.

That is, in the method of amplifying the signal by forming the same p ⁺ πpnn ⁺ structure as that used in the crystalline semiconductor avalanche diode by using amorphous Si and injecting the signal light through the p ⁺ region, It is absorbed and converted into a charge, and the charge is guided to the pn junction, and avalanche multiplication is performed in the region of the depletion layer existing in the pn junction.

However, in order to cause avalanche multiplication, it is necessary to cause the charges to travel over a certain distance, but when actually forming the above structure with amorphous Si, amorphous Si turns into crystalline Si. Compared with this, it was found that the depletion layer in pn matching does not spread so much and the avalanche multiplication effect is not sufficient because there are many localized levels in the forbidden band. Furthermore, when the operating temperature exceeds room temperature, the dark current increases, and it is not possible to apply a high electric field to obtain a sufficient avalanche multiplication effect. As a result, the avalanche diode structure similar to that of crystalline Si is simply amorphous.
There is a problem that a sufficient amplification factor cannot be obtained only by forming with Si.

Further, in the case of the avalanche multiplication method using amorphous Se having a blocking junction, although a large multiplication factor can be obtained and good photoresponse characteristics can be obtained, due to the restrictions of the material itself,
For example, in a high temperature environment of 80 ° C. or higher, there is a possibility that the film may be deteriorated during use, and there is a defect that the device characteristics are not sufficient especially during high temperature operation.

An object of the present invention is to eliminate the above-mentioned conventional problems, and provide an amorphous semiconductor light receiving element having a photoelectric conversion gain of more than 1, good photoresponse characteristics, and excellent heat resistance.

[Means for Solving the Problems] The above object includes at least one of hydrogen and a halogen element inside the light receiving device (the content is 0.5 to 30 atomic percent, more preferably 5 to 20 atomic percent). A structure in which an amorphous semiconductor layer mainly containing a tetrahedral element is provided, and an electrical junction having a property of preventing injection of charges from the outside is provided between the amorphous semiconductor layer and an external electrode. Then, an electric field is applied to the amorphous semiconductor layer, and the amorphous semiconductor layer is operated so as to generate a charge multiplication action mainly in a region other than the junction interface.

The inventors of the present invention used carbon as a tetrahedral element,
Experiments were conducted using silicon, germanium, tin, and the like.

The present inventors have already discovered that when a strong electric field is applied to an amorphous semiconductor layer mainly composed of Se, a charge multiplication action occurs inside the amorphous semiconductor layer. Until now, it has been generally considered that such a phenomenon is extremely unlikely to occur in the semiconductor itself because an amorphous semiconductor has many internal defects.
The amorphous Se discovered at this time was considered to be an exceptional material.

This time, the present inventors, the above phenomenon is not necessarily limited to amorphous Se, it is possible to form a blocking junction by using the above tetrahedral amorphous material containing hydrogen or halogen, Furthermore, unlike the conventional method in which a pn junction is formed with such a material and avalanche amplification is performed in the depletion layer portion of the junction, the blocking type junction structure described above is adopted to apply a high voltage to the depletion layer due to the junction. It has been discovered that, when applied and operated in a region having no region inside the amorphous layer, a charge doubling action similar to that in the case of Se can occur inside the tetrahedral amorphous layer. By using the above-mentioned method of applying a strong electric field to the amorphous layer to generate the charge multiplication effect in the amorphous layer, the excellent light response characteristics of the light receiving element having the blocking structure are deteriorated. It is possible to obtain a photoelectric conversion device having a high sensitivity with a gain larger than 1 without performing the above.

As a result of further investigation, as a tetrahedral amorphous material forming the above-mentioned blocking structure, if a material with a forbidden band width wider than 1.85 eV is selected, the characteristics do not deteriorate even at a temperature of 80 ° C. or higher, and It was found that the stability during operation was particularly excellent.

It was also found that a sufficient multiplication factor can be obtained when the thickness of the amorphous layer is about 0.5 to 10 μm.

FIG. 1 is a principle configuration diagram of a photoelectric conversion device when the present invention is carried out. Substrate 1, signal readout electrode 2 having a thickness of 3000 Å or less, charge injection blocking layer 3 having a thickness of 0.5 to 5000 Å,
A photoconductive layer 4 containing an amorphous semiconductor having a charge multiplication effect with a thickness of about 0.5 to 10 μm, a layer 5 with a thickness of about 50 to 5000 Å for blocking the injection of charges having the opposite sign to 3, and a counter electrode 6 are basically used. It is a part. However, here, if sufficient rectifying contact is obtained between the photoconductive film 4 and the electrode 2 or the electrode 6, the charge injection blocking layer 3 or 5 may be omitted.

[Operation] An electric field necessary for causing avalanche multiplication in the amorphous semiconductor layer is applied to the photoelectric conversion device having the structure shown in FIG. As discovered by the inventors, in an element in which the amorphous semiconductor layer has a blocking junction structure formed of a tetrahedral material containing hydrogen or halogen, a high electric field can be applied to the entire amorphous semiconductor layer and The dark current can be reduced to 1/100 or less of that of a crystalline semiconductor despite its area.

When light is irradiated from the transparent conductive film side in this state, the incident light is absorbed in the amorphous layer to generate electron-hole pairs, and travel in opposite directions in the directions determined by the direction of the applied voltage.
Therefore, of the primary photocurrents generated in the adopted amorphous body, the one with a higher ionization rate is amorphous so that the charge multiplication effect effectively occurs when traveling in the amorphous layer under a high electric field. By setting the thickness of the quality layer and the direction of the electric field, the gain is higher than 1 and the sensitivity is high while maintaining the high-speed photoresponse characteristics.
Moreover, it is possible to obtain device characteristics that operate stably even at 80 ° C or higher.

Further, the present invention is extremely effective in that an amorphous semiconductor is easy to form a thin film having a large area and can be deposited on an arbitrary substrate by a simple process, and a uniform multiplication factor can be obtained. .

Examples of desirable tetrahedral amorphous semiconductor materials for carrying out the present invention include compounds containing Si as a main component. This compound has the characteristics that the band gap can be changed by changing the production conditions and the composition ratio of Si, and is also excellent in heat resistance.

Further, in the configuration of FIG. 1, when the charge injection blocking layer is provided to enhance the charge injection blocking contact, the layers described below are effective.

That is, as the hole injection blocking layer, amorphous silicon carbide or silicon nitride containing at least one of hydrogen or a halogen element, or at least one of hydrogen or a halogen element and a group V element such as P or As is used. Amorphous silicon carbide or silicon nitride containing at least one of the above, or
An oxide of at least one of Ce, Ge, Zn, Cd, Al, Si, Nb, Ta, Cr and W, or a combination of two or more of the above layers is suitable.

As the electron injection blocking layer, amorphous silicon carbide or silicon nitride containing at least one of hydrogen or a halogen element, or at least one of hydrogen or a halogen element and at least a Group III element such as B or Al is used. Amorphous silicon carbide or silicon nitride, or Ir
Oxide, or Sb ₂ S ₃ , As ₂ S ₃ , As ₂ Se ₃ , Se-As-Te
Chalcogenides such as or a combination of two or more of the above layers are suitable.

The photoelectric conversion device using the charge multiplication function in the tetrahedral amorphous semiconductor layer has been described above.However, unlike a crystal, an amorphous semiconductor can be formed by stacking arbitrary different materials. Alternatively, a structure in which two or more different types of amorphous semiconductor layers having the same charge multiplication effect are laminated may be used. Further, the entire photoconductive layer does not necessarily have to be an amorphous semiconductor, and a crystalline semiconductor and an amorphous semiconductor may be used. It may have a structure in which high quality semiconductor layers are laminated, or may have a structure in which it is deposited on a signal reading circuit board or the like. What is required in the present invention is that at least a part of the layers constituting the photoconductive layer is made of an amorphous semiconductor having a large heat resistance and a wide band gap without having a depletion layer region due to a junction, and is strong. The purpose is to apply an electric field to cause a charge multiplication effect inside the amorphous semiconductor layer to enhance the sensitivity.

2 and 3 show the effects of implementing the present invention. FIG. 2 shows a transparent electrode, a transparent electrode, an electron injection blocking layer, an intrinsic amorphous silicon layer, a hole injection blocking layer, and an Al layer on a transparent glass substrate.
Amorphous silicon was used on the light receiving element (A) with an effective area of 1 cm ² and the transparent electrode on which the transparent electrode was deposited.
A p ⁺ πpnn ⁺ junction is formed, and an Al electrode is deposited on the p ⁺ π pnn ⁺ junction. In the light receiving element (B) with an effective area of 1 cm ² , the entire area within the amorphous silicon layer in the case of (A), and in the case of (B) The temperature dependence of the dark current and the gain of photoelectric conversion when an electric field is applied so that avalanche multiplication is obtained in the depletion layer portion of the pn junction is shown. In the light receiving element (B), the gain is insufficient over the entire temperature range, and the dark current increases significantly with the temperature rise, whereas in the light receiving element (A), both the gain and the dark current are good. Shows behavior.

Next, FIG. 3 shows the above-mentioned device (A) and a light-receiving device having an effective area of 1 cm ² in which a transparent electrode, a hole injection blocking layer, an amorphous Se layer, and an Au electrode are sequentially arranged on a transparent substrate. The element damage rate when (C) is continuously operated at 80 ° C. for 100 hours is shown. Element (C)
In the case of the element (A), the breakage rate is significantly lower than that of (1).

By the way, in the above, an example in which the avalanche effect in the thermally stable tetrahedral amorphous semiconductor is mainly applied to the photoelectric conversion device has been described, but the present invention is not limited to the photoelectric conversion device and is more general. It goes without saying that it can be applied to an amplifying element and a switching element.

 Hereinafter, the present invention will be described in detail with reference to Examples.

Example 1 A transparent electrode 2 mainly composed of iridium oxide is formed on a transparent substrate 1. On top of that, as a photoconductive layer 4 containing an amorphous semiconductor, SiH ₄ is used as a source gas and a film thickness is 0.5 to 10 μm.
A-Si: H is formed by the plasma CVD method. On top of that, SiH
₄ and C ₂ H ₆ as source gas, PH ₃ as doping gas, and P as
A hole injection blocking layer 5 is formed by forming a-SiC: H doped with 50 ppm to a thickness of 10 nm. On top of that, as the counter electrode 6, Al
Electrodes are deposited to obtain the photoelectric conversion device shown in FIG.

Embodiment 2 FIG. 4 shows the structure of a one-dimensional image sensor which is an embodiment of the present invention. FIG. 4 (a) is a view showing a part of the plane, and FIG. 4 (b) is a view showing a cross section taken along the line AA 'in FIG. 4 (a).

After depositing a transparent conductive film mainly composed of iridium oxide on the transparent substrate 11, the conductive film is separated by photoetching to form individual reading electrodes 12. Then, using a mask, SiH ₄ and C ₂ H ₆ are used as source gases, and B ₂ H ₆ is used as a doping gas.
The electron injection blocking layer 13 is formed to a thickness of nm. Further thereon, a photoconductive layer 14 containing an amorphous semiconductor is formed using the same mask.
As a step, a Si target is sputtered using a mixed gas of Ar and H ₂ to form a-Si: H having a film thickness of 0.5 to 10 μm. Further, using the same mask, using SiH ₄ and C ₂ H ₆ as source gases and PH ₃ as a doping gas, a-SiC: H doped with 50 ppm of P is formed to a thickness of 10 nm to prevent hole injection. Tier 1
Set to 5. Further, an Al electrode is deposited as the common electrode 16 on it using a mask different from the above. After that, the reading electrode 12 is connected to the scanning circuit provided on the substrate by means such as bonding to obtain a one-dimensional image sensor.

When an electric field of 5 × 10 ⁷ V / m or more was applied to the photoelectric conversion devices of Examples 1 and 2 in the direction in which the transparent substrate side was negative with respect to the counter electrode, the gain was obtained without impairing the optical response characteristics. High sensitivities exceeding 1 were realized, and even when they were continuously operated at 80 ° C. for a long time, no characteristic change occurred.

Embodiment 3 FIG. 5 shows a block diagram of an image pickup tube which is another embodiment of the present invention. A transparent electrode 19 mainly composed of In ₂ O ₃ on the glass substrate 18
To form. On top of that, PH ₄ as a doping gas,
A hole injection blocking layer 20 is formed by forming a-Si: H doped with 50 ppm of P to a thickness of 10 nm. Next, using SiH ₄ as a source gas, a-Si: H having a film thickness of 0.5 to 10 μm is formed by the plasma CVD method to obtain the photoconductive layer 21. Next, Sb ₂ S ₃ is used as an electron injection blocking layer.
Deposit to a film thickness of 100 nm in an Ar atmosphere of 0 ^-1 Torr. From the above 18 to 22, the image pickup tube target portion is obtained. This target portion is incorporated into a glass tube 17 including a cathode 171, an electron beam deflection / focusing electrode 172, and vacuum exhausted to obtain an image pickup tube.

Example 4 Next, as in Example 3, an example in which the present invention is applied to an image pickup tube will be described. In this embodiment, Ge is used as the tetrahedral element. In FIG. 5, on the glass substrate 18,
A transparent electrode 19 mainly composed of In ₂ O ₃ is formed, and PH ₄ is formed on the transparent electrode 19.
A-Si doped with 50 ppm of P as a doping glass:
H is formed to a thickness of 10 nm to form the hole injection blocking layer 20. Next, using GeH ₄ as a source gas, a film thickness of 0.5 is obtained by the plasma CVD method.
The photoconductive layer 21 is obtained by forming a-Ge: H of about 10 μm. Next, as an electron injection blocking layer, an amorphous material composed of Se-As-Te is deposited to a film thickness of 100 nm in an N ₂ atmosphere of 10 ^-1 Torr. Example 3 using the image pickup tube target portion thus obtained
An image pickup tube is obtained by a method similar to.

In the image pickup tubes of Examples 3 and 4, when an electric field of 8 × 10 ⁷ V / m or more is applied in the direction in which the transparent electrode is positive, high sensitivity exceeding gain 1 can be realized without deteriorating the light response characteristic. , It was confirmed that the operation was thermally stable.

[Effects of the Invention] As is apparent from the above, according to the present invention, the gain is higher than 1 and the high sensitivity is achieved without deteriorating the excellent light response characteristics of the light receiving element using the photoconductive film having the blocking structure. A photoelectric conversion device that is thermally stable can be obtained.

[Brief description of drawings]

2 is a diagram showing the dark current of the light receiving element and the temperature dependence of the gain of photoelectric conversion, FIG. 3 is a diagram showing the damage rate of the light receiving element,
FIG. 1 is a diagram showing a principle configuration of a photoelectric conversion device having a charge injection blocking structure, FIG. 4 is a configuration diagram of a one-dimensional image sensor which is one embodiment of the present invention, and FIG. It is a block diagram of the image pick-up tube which is one Example of the invention. 1 ... Substrate, 2 ... Signal reading electrode 3 ... Charge injection blocking layer, 4 ... Photoconductive layer, 5 ... Charge injection blocking layer, 6 ... Counter electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenji Samejima, 1-280 Higashi Koigakubo, Kokubunji City, Tokyo Metropolitan Institute of Hitachi, Ltd. (72) Hirokazu Matsubara 1-280, Higashi Koigakubo, Kokubunji City, Tokyo Hitachi, Ltd. Central Research Laboratory (72) Inventor Yoshio Ishioka 1-280 Higashi Koigakubo, Kokubunji, Tokyo Central Research Laboratory, Hitachi, Ltd. (72) Inventor Keiichi Shitara 1-10-11 Kinuta, Setagaya-ku, Tokyo Broadcasting Technology of Japan Broadcasting Corporation Inside the laboratory (72) Inventor Tatsuro Kawamura 1-10-11 Kinuta, Setagaya-ku, Tokyo Inside the Broadcasting Technology Laboratory, Japan Broadcasting Corporation (72) Inventor Kazuhisa Takeshi 1-10-11 Kinuta, Setagaya-ku, Tokyo Japan (72) Inventor Kenkichi Tanioka 1-10-11 Kinuta, Setagaya-ku, Tokyo Japan (72) Inventor Junichi Yamazaki, 1-10-11 Kinuta, Setagaya-ku, Tokyo Inside Broadcasting Technology Institute, Japan Broadcasting Corporation

Claims (2)

[Claims] 1. A photoelectric conversion device having a photoconductive layer containing at least an amorphous semiconductor layer, wherein the amorphous semiconductor layer is mainly composed of silicon and contains at least one of hydrogen and a halogen element, and the photoconductive layer comprises , Between the external electrodes,
It has an electric junction structure having a property of preventing the injection of charges from the outside, applies an electric field to the amorphous semiconductor layer, and increases the charge mainly in the region other than the interface of the junction in the amorphous semiconductor layer. A photoelectric conversion device which is operated by causing a double action. 2. An amorphous semiconductor mainly composed of silicon, which is used for the photoconductive layer and which has a charge multiplication effect, is 1.85.
The photoelectric conversion device according to claim 1, wherein the photoelectric conversion device has a forbidden band width exceeding eV.