JP2021068827A - Photoelectric conversion element, method for manufacturing the same, and laminate-type image pickup element - Google Patents

Abstract

To provide a photoelectric conversion element which allows a photoelectric current value stable in time to be obtained while a reverse bias voltage is applied thereto.SOLUTION: A photoelectric conversion element 1 comprises a crystal selenium film 30 used as a photoelectric conversion part, and a gallium oxide film 10 which forms a pn junction with the crystal selenium film. In the photoelectric conversion element, the gallium oxide film is doped with tin so that an atomic concentration of the tin in the gallium oxide film is 6.0 atm% or more and 9.0 atm% or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a photoelectric conversion element, a method for manufacturing the same, and a laminated image pickup element, and more particularly to a photoelectric conversion element having sensitivity over the entire visible light range and having a photoelectric conversion unit made of a crystalline selenium film.

In recent years, the definition of video systems has rapidly increased, and in the image sensor, a decrease in sensitivity has become a technical issue due to the miniaturization of pixels. Therefore, research is being conducted on a technique for increasing the sensitivity of a camera by using a stacked image pickup device in which a photoelectric conversion element having high absorption characteristics is applied to a photoelectric conversion unit.

In order to realize a high-sensitivity camera for visible light, the photoelectric conversion element is required to have high sensitivity (external quantum efficiency) over the entire visible light range. The crystalline selenium film has a bandgap energy of about 1.8 eV and is promising as a material having sensitivity over the entire visible light range. As the photoelectric conversion element using the crystalline selenium film for the photoelectric conversion unit, those using the Schottky junction between the crystalline selenium film and the ITO film which is a conductive metal oxide, the crystalline selenium film and the semi-insulating metal oxide are used. (For example, Non-Patent Document 1, Non-Patent Document 2, Patent Document 1) have been reported using the pn junction of.

Then, as a photoelectric conversion element using a pn junction, a pn junction type photoelectric conversion element in which a p-type crystalline selenium film and an n-type semi-insulating metal oxide gallium oxide film are bonded has been reported. ing. This photoelectric conversion element uses the large bandgap energy of gallium oxide to block hole injection from an external electrode, thereby reducing a dark current when an external electric field is applied. In addition, by adding (doping) tin to gallium oxide, the carrier concentration of gallium oxide is increased, and the depletion layer is efficiently expanded on the crystalline selenium side, enabling low-voltage operation of the photoelectric conversion element. It has been reported (Non-Patent Document 3, Patent Document 2).

Japanese Unexamined Patent Publication No. 61-67279 Japanese Unexamined Patent Publication No. 2015-225886

Tokio Nakada et al., “Efficient ITO / Se Heterojunction Solar cells”. Japanese Journal of Applied Physics, Vol. 23, No. 8, pp. L587-L589 (1984) S. Imura et al., “Low-voltage-operation avalanche photodiode based on n-gallium oxide / p-crystalline selenium heterojunction”, Applied Physics Letters, Vol. 104, No. 24, pp. 242101-242101-4 (2014) ) Kenji Kikuchi et al., “Electrical and optical properties of Ga2O3 / CuGaSe2heterojunction photoconductors, Thin Solid Films, Vol. 550, pp. 635-637 (2014)

The photoelectric conversion element (photoelectric conversion film) disclosed in Non-Patent Document 3 and Patent Document 2 is intended to increase the sensitivity of the photoelectric conversion element by low voltage operation. The present inventors have attempted to fabricate a photoelectric conversion element provided with a tin-doped gallium oxide film proposed in Non-Patent Document 3 and Patent Document 2. Then, the present inventors have experimentally confirmed for the first time that the photocurrent value of the photoelectric conversion element when a reverse bias voltage is applied is unstable every time the measurement is performed with the tin doping amount conventionally proposed. If the photocurrent value when a reverse bias voltage is applied to the photoelectric conversion element is unstable, applying this to the stacked image sensor will lead to the generation of afterimages. Therefore, an object of the present invention is to provide a photoelectric conversion element capable of obtaining a time-stable photocurrent value when a reverse bias voltage is applied.

In order to solve the above problems, the present inventors diligently studied and conceived the amount of tin doped into gallium oxide. Then, the present inventors have experimentally demonstrated that the photocurrent value when a reverse bias voltage is applied to the photoelectric conversion element can be stabilized by increasing the doping amount as compared with the tin doping amount proposed by the prior art. confirmed. The stacked image sensor using this photoelectric conversion element can effectively suppress the influence of afterimages. The present invention has been completed based on the above findings, and its gist structure is as follows.

The photoelectric conversion element according to the present invention includes a tin-doped gallium oxide film, a crystalline selenium film, and a bonding film for joining the gallium oxide film and the crystalline selenium film, and the tin in the gallium oxide film. It is characterized in that the atomic percentage is 6.0 atom% or more and 9.0 atom% or less.

In this photoelectric conversion element, the film thickness of the gallium oxide film is preferably 2 nm to 100 nm.

Further, the photoelectric conversion element according to the present invention preferably includes a substrate, a first electrode, a gallium oxide film, a bonding film, a crystalline selenium film, and a second electrode in this order.

Further, the method for manufacturing a photoelectric conversion element according to the present invention includes a step of forming a tin-doped gallium oxide film, a step of forming a bonding film on the gallium oxide film, and a crystalline selenium film on the bonding film. In the step of forming the gallium oxide film including the step of forming, the gallium oxide using a target so that the atomic percentage of the tin in the gallium oxide film is 6.0 atom% or more and 9.0 atom% or less. Is characterized by forming a film.

Further, the stacked image pickup device according to the present invention is characterized by including the photoelectric conversion element.

According to the present invention, it is possible to provide a photoelectric conversion element capable of obtaining a time-stable photocurrent value when a reverse bias voltage is applied.

It is a schematic cross-sectional view explaining the photoelectric conversion element according to one Embodiment of this invention. It is a schematic cross-sectional view explaining the photoelectric conversion element according to the preferred embodiment of this invention. It is a schematic cross-sectional view of the sample 1 to 4 prepared in the preliminary experiment example 1. FIG. It is an energy figure obtained in the preliminary experiment example 1. It is a transmission spectrum in the visible light region measured in the preliminary experiment example 1. It is a schematic cross-sectional view of the sample 5-8 prepared in the preliminary experiment example 2. FIG. It is a graph of the voltage-photocurrent characteristic measured in Experimental Example 1.

Hereinafter, a photoelectric conversion element according to the present invention, a method for manufacturing the same, and an embodiment of a stacked image sensor will be described with reference to the drawings. In principle, the same components are given the same reference number, and duplicate explanations are omitted. In each figure, for convenience of explanation, the aspect ratio of each configuration is exaggerated from the actual ratio.

(Photoelectric conversion element)
A photoelectric conversion element 1 according to an embodiment of the present invention will be described with reference to FIG. The photoelectric conversion element 1 includes at least a tin (Sn) -doped gallium oxide film 10, a bonding film 20, and a crystalline selenium film 30. The bonding film 20 joins the gallium oxide film 10 and the crystalline selenium film 30, and in FIG. 1, the bonding film 20 is sandwiched between the gallium oxide film 10 and the crystalline selenium film 30. The gallium oxide film 10 is doped with tin, and the atomic percentage of tin in the gallium oxide film 10 is 6.0 atom% or more and 9.0 atom% or less. The value of the atomic percentage of tin in the present specification can be measured by the Rutherford backscattering analysis method (RBS), and in the examples described later, the value measured by the Rutherford backscattering analysis method is adopted. Hereinafter, details of each configuration will be described in sequence.

<Gallium oxide film>
The gallium oxide film 10 functions as an n-type semiconductor in the photoelectric conversion element 1. Here, the atomic percentage of tin (Sn) in the tin-doped gallium oxide film 10 is set to 6.0 atom% or more and 9.0 atom% or less.

The reason for limiting the tin doping amount to the above range will be described. The present inventors have experimentally confirmed that when tin is doped into the gallium oxide film 10, the energy in the conduction band is reduced and the band gap is reduced while maintaining the energy in the valence band. Therefore, by optimizing the doping amount of tin, the band offset (ΔE) of the conduction band can be reduced between gallium oxide and crystalline selenium. This is considered to be the reason why a time-stable photocurrent value can be obtained when the reverse bias voltage is applied. Therefore, the tin content in the gallium oxide film 10 is set to 6.0 atom% or more in terms of atomic percentage. Further, if tin is doped in the gallium oxide film 10 in the above range, it is preferable from the viewpoint that the operating voltage of the photoelectric conversion element 1 can be reduced. On the other hand, if the tin content in the gallium oxide film 10 is set to 9.0 atom% or less in terms of atomic percentage, excessive carrier generation due to tin doping can be suppressed and an increase in dark current of the photoelectric conversion element 1 can be prevented. .. In order to obtain the effect of the present invention more reliably, the tin content in the gallium oxide film 10 is preferably 6.5 attom% or more in terms of atomic percentage, and more preferably 7.0 atom% or more.

The film thickness of the gallium oxide film 10 is not particularly limited, but is preferably 2 nm or more and 100 nm or less. When the film thickness of the gallium oxide film 10 is 2 nm or more, the hole injection charge from the electrode can be efficiently blocked. Further, when the film thickness of the gallium oxide film 10 is 100 nm or less, more preferably 50 nm or less, the externally applied voltage is efficiently applied to the crystal selenium film 30 side.

<Joint film>
The material of the bonding film 20 is not particularly limited as long as the gallium oxide film 10 and the crystalline selenium film 30 can be bonded, but the bonding film 20 may consist of one selected from the group consisting of tellurium (Te), bismuth (Bi), and antimony (Sb). Preferably, tellurium is more preferably used in order to reliably bond the gallium oxide film 10 and the crystalline selenium film 30.

The film thickness of the bonding film 20 is not particularly limited, but can be 0.1 nm or more and 10 nm or less. When the film thickness of the bonding film 20 is 0.1 nm or more, the adhesive force between the gallium oxide film 10 and the crystalline selenium film 30 can be effectively increased, which is preferable. Further, when the film thickness of the bonding film 20 is 10 nm or less, more preferably 3 nm or less, the bonding film 20 can prevent the formation of defects in the crystal selenium film 30, so that an increase in dark current can be suppressed, which is preferable. .. The bonding film 20 may be continuously formed over the entire area between the gallium oxide film 10 and the crystalline selenium film 30 as illustrated in FIG. However, if the bonding between the gallium oxide film 10 and the crystalline selenium film 30 is ensured, a hole is provided in a part of the bonding film 20 in the in-plane direction so that the gallium oxide film 10 and the crystalline selenium film 30 come into contact with each other. It may be formed.

<Crystal selenium film>
The crystalline selenium film 30 is a photoelectric conversion unit in the photoelectric conversion element 1 and functions as a p-type semiconductor. The film thickness of the crystalline selenium film 30 is not particularly limited, but is preferably 0.1 μm or more. When the film thickness of the crystalline selenium film 30 is 0.1 μm or more, preferably 0.5 μm or more, the film thickness is sufficient, so that the photoelectric conversion element 1 can obtain sufficient sensitivity in the entire visible light range. The upper limit of the film thickness of the crystalline selenium film 30 is not particularly limited, but when it is 5 μm or less, preferably 2 μm or less, the crystalline selenium film 30 can be efficiently formed, which is preferable from the viewpoint of productivity.

As described above, in the photoelectric conversion element 1 according to the present invention, since the tin content of the gallium oxide film 10 is 6.0 atom% or more and 9.0 atom% or less, a time-stable photocurrent value when a reverse bias voltage is applied. Is obtained.

Although the preferable range of the film thickness of the gallium oxide film 10 in the photoelectric conversion element 1 is as described above, it is preferable to set the film thickness separately in order to evaluate and experiment with the physical properties of the gallium oxide film 10. When the transmittance of the tin-doped gallium oxide film 10 is measured with a spectrophotometer or the like, or when the band gap is measured with a spectrophotometer or the like, the thickness of the gallium oxide film 10 is preferably 100 nm or more. .. Further, when the ionization energy of the gallium oxide film 10 is measured by X-ray photoelectron spectroscopy (XPS) and when the Sn concentration (atomic percentage) in the gallium oxide film 10 is measured by the Rutherford backscattering analysis method (RBS). The thickness of the gallium oxide film 10 is preferably 20 nm or more. In these evaluation experiments, a gallium oxide film may be directly formed on the substrate and the evaluation experiment may be performed.

Next, refer to FIG. The photoelectric conversion element 2 according to the preferred embodiment of the present invention includes the gallium oxide film 10, the bonding film 20, and the crystalline selenium film 30 described above, and joins the first electrode 50 and the gallium oxide film 10 in this order from the substrate 40. The film 20, the crystalline selenium film 30, and the second electrode 60 are provided in this order. The configurations other than the gallium oxide film 10, the bonding film 20, and the crystalline selenium film 30 described above will be further described below.

As the substrate 40, for example, a glass substrate, a sapphire substrate, a silicon substrate, or the like can be used, and may be appropriately selected depending on the application of the photoelectric conversion element 2 and the material of the first electrode 50 formed on the substrate 40.

Examples of the first electrode 50 provided on the substrate 40 include transparent oxide conductive films such as ITO (indium tin oxide), IZO (zinc oxide tin), and AZO (aluminum-added participating zinc), as well as Al, Au, and Al, Au. A metal film such as Ti, Nb, W, or Mo can be used. The material of the second electrode 60 provided on the opposite side of the substrate 40 is the same as that of the first electrode, and the materials of both may be different or the same. Further, it is preferable that at least the electrode material on the light receiving surface side of the photoelectric conversion element 2 is a transparent material.

(Stacked image sensor)
Further, the photoelectric conversion elements 1 and 2 according to the present invention described above can be applied to a stacked image sensor. For example, a stacked image pickup device can be obtained by joining a semiconductor substrate such as a silicon substrate provided with a signal readout circuit and pixel electrodes to the photoelectric conversion elements 1 and 2 according to the present invention.

(Manufacturing method of photoelectric conversion element)
An embodiment of a method for manufacturing a photoelectric conversion element 1 according to the present invention will be described with reference to FIG. The method for manufacturing the photoelectric conversion element 1 includes a step of forming a tin-doped gallium oxide film 10, a step of forming a bonding film 20 on the gallium oxide film 10, and a step of forming a crystalline selenium film 30 on the bonding film 20. Including the process of Then, in the step of forming the gallium oxide film 10, gallium oxide is formed by forming a gallium oxide film using a target so that the atomic percentage of tin in the gallium oxide film 10 is 6.0 atom% or more and 9.0 atom% or less. Form 10. Hereinafter, each step will be sequentially described including the optional configuration shown in FIG. The same components are given the same reference numbers, and the description of the material, film thickness, etc. of each component is as described above, and duplicate description will be omitted.

<Gallium oxide film forming process>
Referring to FIG. 2, the gallium oxide film 10 is formed on the first electrode 50. In order to form the gallium oxide film 10, first, the first electrode 50 may be formed on the substrate 40. The first electrode can be formed by using a vacuum vapor deposition method, a sputtering method, or the like. Next, the gallium oxide film 10 is formed on the first electrode 50 by using a sputtering method, a pulse laser vapor deposition method, a vacuum vapor deposition method, or the like.

Here, as described above, gallium oxide is formed into a film using a target made of tin-containing gallium oxide so that the atomic percentage of tin in the gallium oxide film 10 is 6.0 atom% or more and 9.0 atom% or less, and the gallium oxide is oxidized. A gallium film 10 is obtained. For example, the gallium oxide film 10 can be formed using a single target made of metallic tin or tin oxide-containing gallium oxide. The tin content in the gallium oxide film 10 is roughly proportional to the tin content in the target, but is not linear. Therefore, the tin content in the gallium oxide film 10 after film formation obtained is determined according to the output conditions (RF power, etc.), atmospheric gas conditions (oxygen partial pressure, etc.), and the tin content of the target. Further, instead of a single target made of tin-containing gallium oxide, a tin metal target or a tin oxide sintered body target and a target made of gallium oxide can be co-sprayed to contain desired tin. An amount of gallium oxide film 10 can be formed.

<Formation process of bonding film>
After forming the gallium oxide film 10 described above, the bonding film 20 is formed on the gallium oxide film 10. In order to form the bonding film 20, a vacuum vapor deposition method, a sputtering method or the like may be used.

<Crystal selenium film forming process>
Then, the crystalline selenium film 30 is formed on the bonding film 20. In order to form the crystalline selenium film 30, first, an amorphous selenium film is formed on the bonding film 20. In order to form an amorphous selenium film, a vacuum vapor deposition method, a sputtering method, or the like may be used. Then, for example, by heat-treating at a temperature of 100 ° C. to 220 ° C. for 30 seconds to 1 hour, the amorphous selenium film can be crystallized to obtain the crystalline selenium film 30. The heat treatment temperature and heat treatment time are examples, and the heat treatment time is not limited to this condition, but it is preferable that the heat treatment temperature and the heat treatment time are within the above ranges because a crystalline selenium film 30 having good crystallinity can be obtained. Further, the second electrode 60 can be formed on the crystal selenium film 30 by using a vacuum vapor deposition method, a sputtering method or the like.

The atmosphere at the time of film formation in each step is not particularly limited, and general film formation conditions can be used. Further, in order to enhance the crystallinity of the gallium oxide film 10, it is also preferable to form the gallium oxide film 10 in an oxygen atmosphere. For this purpose, the oxygen partial pressure ^{is preferably 8.0 × 10 -3} Pa or more and 1.0 × 10 ^-1 Pa or less, preferably 7.5 × 10 ^-3 Pa or more and 3.0 × 10 ^-2 Pa or less. It is more preferable to do so.

By going through each step including the above optional steps, a photoelectric conversion element according to the present invention can be manufactured, and this photoelectric conversion element can obtain a time-stable photocurrent value when a reverse bias voltage is applied.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples. First, in Preliminary Experimental Example 1, a gallium oxide film was formed using gallium oxide targets having different tin contents, and while evaluating the tin content in the obtained gallium oxide film, the bandgap energy of the gallium oxide film and the band gap energy of the gallium oxide film were evaluated. The transmittance was evaluated. In Preliminary Experiment Example 2, it was confirmed that the gallium oxide film can be formed even if a substrate made of a material different from that of Preliminary Experiment Example 1 and Experimental Example 1 is used. In Experimental Example 1, it was confirmed that the effect of the present invention could be obtained by satisfying the conditions of the present invention, and the cause was considered.

(Preliminary experiment example 1)
FIG. 3 shows a schematic cross-sectional view of the evaluation film produced in Preliminary Experimental Example 1. For convenience of explanation, the reference numerals in FIG. 3 refer to the components used in FIGS. 1 and 2.

<Sample 1>
A gallium oxide film 10 having a film thickness of 100 nm was formed on a substrate 40 made of glass by an RF sputtering method. The film was formed by setting the substrate temperature during sputtering to room temperature. The target used was a tin-added gallium oxide target with 40 atom% tin added. The oxygen partial pressure at the time of film formation was 1.5 × ^10-2 Pa, and the gallium oxide film 10 was formed with an RF power of 100 W to obtain Sample 1.

<Sample 2>
When the tin-added amount in the tin-added gallium oxide target used in sample 1 was 40 atom%, sample 1 was formed except that the tin-added gallium oxide target in which the tin-added amount was reduced was used to form the gallium oxide film 10. Sample 2 was obtained in the same manner as above.

<Sample 3>
When the amount of tin added in the tin-added gallium oxide target used in Sample 1 was 40 atom%, the amount of tin added was further reduced as compared with that used in Sample 2, and half of the amount added in Sample 1 (that is, 20 atom). Sample 3 was obtained in the same manner as in Sample 1 except that the gallium oxide film 10 was formed using the tin-added gallium oxide target (%).

<Sample 4>
When the amount of tin added in the tin-added gallium oxide target used in sample 1 was 40 atom%, the same procedure as in sample 1 except that tin formed the gallium oxide film 10 using the non-doped gallium oxide target. Sample 4 was obtained.

<Evaluation>
When the band gap energy of each sample was determined using a spectroscopic ellipsometer for each of Samples 1 to 4, 4.6 eV (Sample 1), 4.7 eV (Sample 2), 4.8 eV (Sample 3), 4 It was 9.9 eV (Sample 4), and it was found that the band gap energy decreased as the tin addition amount increased. Furthermore, as a result of measuring the ionization energy of each sample by X-ray photoelectron spectroscopy (XPS), the ionization energy of each sample was 7.6 eV. These results are summarized in the energy diagram of FIG. 4 (Sample 2 is omitted for simplification of the diagram). Note that FIG. 4 also shows the energies of crystalline selenium and ITO. When the amount of tin added increases, the energy in the valence band does not change and the bandgap energy decreases. That is, FIG. 4 shows that the energy of the conduction band increases according to the amount of tin added.

Next, the transmittance spectra of Samples 1 to 4 were measured using a spectral transmittance measuring device. The results are shown in FIG. It is confirmed that the bandgap energy decreases as the amount of tin added increases, so that the transmittance in the visible light region also decreases.

Furthermore, when the Sn content in each of the gallium oxide films 10 of Samples 1 to 4 was measured by Rutherford backward scattering analysis (RBS), the Sn content was 8.7 atom% (Sample 1) and 6. It was 1 atom% (sample 2), 4.0 atom% (sample 3), and 0 atom% (sample 4: non-doped).

(Preliminary experiment example 2)
FIG. 6 shows a schematic cross-sectional view of the evaluation film produced in Preliminary Experimental Example 2. For convenience of explanation, the reference numerals in FIG. 3 refer to the components used in FIGS. 1 and 2.

<Sample 5>
A first electrode 50 (transparent conductive film) made of an ITO film having a film thickness of 30 nm was formed on a substrate 40 made of silicon by a sputtering method. Next, a gallium oxide film 10 having a film thickness of 100 nm was formed on the first electrode 50 by an RF sputtering method. In the above-mentioned preliminary experiment example 1, when the gallium oxide film 10 was formed on the substrate 40 made of glass, the film forming conditions were the same as those of the sample 1 except that the gallium oxide film 10 was replaced with the first electrode 50 made of ITO. The same applies to the sputtering target that was used.

<Samples 6-8>
The evaluation films of Samples 6 to 8 were obtained in the same manner as in Sample 5, except that the sputtering targets used in Sample 5 were replaced with the same sputtering targets used in Samples 2 and 4, respectively.

It was confirmed that the gallium oxide film could be formed on the ITO film in all of the samples 6 to 8.

(Experimental Example 1)
The details of Experimental Example 1 will be described with reference to FIG. 2 described above.

<Sample 11 (Example of Invention)>
A first electrode 50 made of an ITO film having a film thickness of 10 nm was formed on a substrate 40 made of glass by a sputtering method. Next, a gallium oxide film 10 having a film thickness of 20 nm was formed by a sputtering method. The target used was the same as that used in the above-mentioned sample 1, and the film forming conditions were the same as those used in the preparation of the sample 1. Next, a bonding film 20 made of a tellurium film having a film thickness of 1 nm was formed by a vacuum vapor deposition method. Subsequently, an amorphous selenium film having a film thickness of 0.3 μm was formed on the bonding film 20 by a vacuum vapor deposition method. Then, the entire substrate 40 on which the first electrode 50, the gallium oxide film 10, the bonding film 20 and the amorphous selenium film were formed was heat-treated at 200 ° C. for 1 minute, and the same film thickness (0.3 μm) was obtained from the amorphous selenium film. ) Crystal selenium film 30 was obtained. Finally, a second electrode 60 made of an ITO film having a film thickness of 30 nm was formed by a sputtering method to obtain a photoelectric conversion element 2 according to the sample 11.

<Sample 12 (invention example), sample 13-14 (comparative example)>
The photoelectric conversion elements 2 according to the samples 12 to 14 were obtained in the same production conditions as the sample 11 except that the sputtering targets used in the sample 11 were replaced with the same sputtering targets used in the samples 2 to 4, respectively. It was.

The Sn content in each of the gallium oxide films 10 of Samples 11 to 14 was 8.7 atom% (Sample 11), 6.1 atom% (Sample 12), 4.0 atom% in atomic percentage, respectively, as in Samples 1 to 4. (Sample 13), 0 atom% (Sample 14) is considered.

<Evaluation>
The voltage-photocurrent characteristics when a reverse bias voltage was applied to each of the photoelectric conversion elements of Samples 11 to 14 so that the second electrode 60 became a positive electrode were measured. In measuring the voltage-photocurrent characteristics, a light ^{source having a light intensity of 2.5 μW / cm 2} and a wavelength of 550 nm was used. In addition, this characteristic evaluation test was repeated, and the voltage-photocurrent characteristic was measured until there was no difference between the one with the slowest rise of photocurrent and the one with the fastest rise. The results are shown in the graph of FIG. 7, and the photocurrent values of the one with the slowest rise of the photocurrent and the one with the fastest rise of the photocurrent are shown, respectively. Further, FIG. 7B is an enlarged graph of the portion 0 to 1V in FIG. 7A. As can be seen from this graph, when the gallium oxide film 10 is formed using non-doped gallium oxide, the rise of the photocurrent is slow, and it rises at a low voltage as the tin addition amount increases. This is because the carrier concentration of non-doped gallium oxide is lower than that of crystalline selenium and the depletion layer does not spread efficiently on the crystalline selenium side, whereas the addition of tin increases the carrier concentration of gallium oxide, which is efficient. It is considered that the depletion layer spreads on the crystal selenium side.

In addition, when non-doped gallium oxide is used, the photocurrent value changes with each measurement and changes over time, but the time variation of the photocurrent value decreases as the amount of tin added to gallium oxide increases. , It is confirmed that the element operates stably in time. As can be seen from the energy diagram of FIG. 4 above, when the amount of tin added to gallium oxide is increased, the band offset (ΔE) of the conduction band between gallium oxide and crystalline selenium becomes smaller, so that photogeneration occurs. It is considered that the generated electrons easily flow to the external electrode. From FIG. 7, in the sample 11 (tin content: 8.7 atom%) satisfying the tin content of the present invention, there is almost no time variation of the photocurrent value, and even in the sample 12 (tin content: 6.1 atom%). It is confirmed that the time fluctuation of the photocurrent value can be sufficiently suppressed.

Therefore, the photoelectric conversion element according to the present invention can obtain a time-stable photocurrent value when a reverse bias voltage is applied, operates at a low voltage, and is not affected by an afterimage. Therefore, a high-sensitivity imaging device can be manufactured. It will be possible.

According to the present invention, it is possible to provide a photoelectric conversion element capable of obtaining a time-stable photocurrent value when a reverse bias voltage is applied, which is particularly useful in a highly sensitive stacked imaging element.

1, 2 Photoelectric conversion element 10 Gallium oxide film 20 Bonding film 30 Crystalline selenium film 40 Substrate 50 1st electrode 60 2nd electrode

Claims (5)

A tin-doped gallium oxide film and
Crystalline selenium film and
A bonding film for joining the gallium oxide film and the crystalline selenium film is provided.
A photoelectric conversion element having an atomic percentage of tin in the gallium oxide film of 6.0 atom% or more and 9.0 atom% or less. The photoelectric conversion element according to claim 1, wherein the gallium oxide film has a film thickness of 2 nm to 100 nm. The photoelectric conversion element according to claim 1 or 2, wherein the substrate, the first electrode, the gallium oxide film, the bonding film, the crystalline selenium film, and the second electrode are provided in this order. .. The process of forming a tin-doped gallium oxide film and
The step of forming a bonding film on the gallium oxide film and
Including a step of forming a crystalline selenium film on the bonding film.
In the step of forming the gallium oxide film, the gallium oxide is formed using a target so that the atomic percentage of tin in the gallium oxide film is 6.0 atom% or more and 9.0 atom% or less. A method for manufacturing a photoelectric conversion element. A stacked image pickup device comprising the photoelectric conversion element according to any one of claims 1 to 3.

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