Photoelectric conversion film, photoelectric conversion element, method for manufacturing photoelectric conversion film, and method for manufacturing photoelectric conversion element

Abstract

To provide a photoelectric conversion film and a photoelectric conversion element that have a reduced dark current and high light-receiving sensitivity even to near-infrared light.SOLUTION: A photoelectric conversion film according to an embodiment of the disclosed technique includes a Ga2O3 layer and a SnSe layer disposed on the Ga2O3 layer. A photoelectric conversion element includes a first electrode, a Ga2O3 layer disposed on the first electrode, a SnSe layer disposed on the Ga2O3 layer, and a second electrode disposed on the SnSe layer.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a photoelectric conversion film, a photoelectric conversion element, a method for manufacturing a photoelectric conversion film, and a method for manufacturing a photoelectric conversion element. [Background technology]

[0002] Imaging devices that use near-infrared light to capture an image of an object (hereinafter referred to as "imaging device") are used in surveillance cameras, food inspections, etc. In particular, for in-vehicle applications, LiDAR (Light Detection And Ranging), which irradiates the object with near-infrared light and measures the distance to the object from the time it takes for the reflected light reflected by the object to be received, is attracting attention as a key device for autonomous driving technology.

[0003] In the above-mentioned imaging device, in order to accurately obtain information on the object to be imaged, high light receiving sensitivity to near-infrared light is required. However, silicon, which is generally used as a material constituting the photoelectric conversion film of the imaging device, has a low near-infrared light absorption rate and therefore a low light receiving sensitivity to near-infrared light. For this reason, research is being conducted on photoelectric conversion films that have a high near-infrared light absorption rate and a high light receiving sensitivity to near-infrared light.

[0004] Tin selenide (SnSe)-based compound semiconductors are known as materials with high sensitivity to near-infrared light. For example, Non-Patent Document 1 describes a SnSe 2 A photoelectric conversion element is disclosed that includes a photoelectric conversion film made of a thin film and a metal electrode disposed on the photoelectric conversion film.

[0005] On the other hand, as a technology to reduce dark current, which is a source of noise in imaging devices, gallium oxide (Ga 2 O 3 A photoelectric conversion element using a photoelectric conversion film made of ZnO or ZnO has been disclosed (see Patent Document 1 and Non-Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6362257 [Non-patent literature]

[0007] [Non-Patent Document 1] Emma P. Mukhokosi et al., "Band Gap Engineering of Hexagonal SnSe2 Nanostructured Thin Films for Infra-Red Photodetection", Scientific Reports, Vol. 7, No. 1, pp. 1-10 (2017) [Non-Patent Document 2] 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) Summary of the Invention [Problem to be solved by the invention]

[0008] However, the SnSe 2 In the photoelectric conversion film containing selenium, the charge injection from the external electrode cannot be suppressed when a voltage is applied, and therefore the dark current may increase. On the other hand, the photoelectric conversion film made of crystalline selenium disclosed in Patent Document 1 and Non-Patent Document 2 has low light receiving sensitivity to near-infrared light.

[0009] The disclosed technique aims to provide a photoelectric conversion film and a photoelectric conversion element that have reduced dark current and high light-receiving sensitivity to near-infrared light. [Means for solving the problem]

[0010] The photoelectric conversion film according to one embodiment of the disclosed technique is Ga 2 O 3 layer, and the Ga 2 O 3 and a SnSe layer disposed on the layer. Effect of the Invention

[0011] According to the disclosed technique, it is possible to provide a photoelectric conversion film and a photoelectric conversion element that reduce dark current and have high light-receiving sensitivity to near-infrared light. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic cross-sectional view of a photoelectric conversion film according to a first embodiment. [Diagram 2] 1A to 1C are schematic cross-sectional views illustrating each step in a method for producing a photoelectric conversion film according to a first embodiment. [Diagram 3] 3 is a diagram showing absorptance spectra of Example 1 and Comparative Example 1 of the photoelectric conversion film according to the first embodiment. FIG. [Figure 4] 1 is a diagram showing X-ray diffraction patterns of Example 1 and Comparative Example 1 of the photoelectric conversion film according to the first embodiment. [Diagram 5] FIG. 4 is a schematic cross-sectional view of a photoelectric conversion element according to a second embodiment. [Figure 6] 5A to 5C are schematic cross-sectional views illustrating steps in a method for manufacturing a photoelectric conversion element according to a second embodiment. [Figure 7] FIG. 13 is a diagram showing dark current characteristics of Example 2 and Comparative Example 2 of the photoelectric conversion element according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In each drawing, the same components may be denoted by the same reference numerals. In addition, in the description of each drawing, the description of components that are the same as those of components already described will be omitted as appropriate.

[0014] In each drawing, a rectangular coordinate system having an X-axis, a Y-axis, and a Z-axis is used to express directions. The X-axis, the Y-axis, and the Z-axis are mutually perpendicular. The X-direction along the X-axis indicates the width direction of the photoelectric conversion film and the photoelectric conversion element according to the embodiment. The Y-direction along the Y-axis indicates the depth direction of the photoelectric conversion film and the photoelectric conversion element according to the embodiment. The Z-direction along the Z-axis indicates the thickness direction of the photoelectric conversion film and the photoelectric conversion element according to the embodiment. The X-direction and the Y-direction may be referred to as "in-plane directions". The Z-direction may be referred to as "direction perpendicular to the surface". However, these do not limit the orientation of the photoelectric conversion film and the photoelectric conversion element according to the embodiment when used, and the orientation of the photoelectric conversion film and the photoelectric conversion element according to the embodiment is arbitrary.

[0015] In the following description, terms indicating specific directions such as "upper" and "lower" are used as necessary, but these terms are intended to facilitate understanding of the invention in the description with reference to the drawings. In other words, the technical scope of the present invention is not limited by these terms. For example, when "upper" is described, the invention does not always have to be used facing upward. The same applies to the case of describing "lower". In addition, when an arbitrary member such as a film or layer is "upper" or "lower" of another member, this includes cases where the arbitrary member and the other member face each other in contact with each other, as well as cases where the arbitrary member and the other member face each other with another member sandwiched therebetween.

[0016] [First embodiment] <Photoelectric conversion film> The photoelectric conversion film according to the first embodiment will be described.

[0017] <<Configuration>> An example of the configuration of a photoelectric conversion film 10 according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a cross-sectional view of the photoelectric conversion film 10 cut along the XZ plane. As shown in Fig. 1, the photoelectric conversion film 10 includes a SnSe layer 110 and a Ga 2 O 3 In the photoelectric conversion film 10, the SnSe layer 110 is a Ga 2 O 3 It is disposed on layer 120 .

[0018] The SnSe layer 110 is a layer that functions as a photoelectric conversion section in the photoelectric conversion film 10. Specifically, the SnSe layer 110 is a p-type semiconductor layer that has a thickness in the direction perpendicular to the surface and extends in the in-plane direction. However, the conductivity type of the SnSe layer 110 is not limited to this.

[0019] The SnSe in the SnSe layer 110 is preferably single crystal or polycrystalline. Single crystal or polycrystalline SnSe has a band gap energy of about 1.0 eV. The wavelength of light having an energy of 1.0 eV is about 1240 nm. Therefore, the SnSe layer 110 absorbs light in a wavelength range shorter than about 1240 nm.

[0020] Incidentally, "near-infrared light" refers to light that belongs to a wavelength range of about 800 nm to about 2500 nm. Therefore, the wavelength range of light that the SnSe layer 110 can absorb overlaps at least part of the wavelength range of near-infrared light. In other words, the SnSe layer 110 has sensitivity to near-infrared light. The absorption characteristics of near-infrared light in the SnSe layer 110 will be described in detail later with reference to FIG. 3.

[0021] The near-infrared light absorbed by the SnSe layer 110 is not limited to light in the wavelength region shorter than 1240 nm. In other words, depending on the internal state of SnSe, such as defects or impurities, and the external environment, such as temperature, the SnSe layer 110 absorbs near-infrared light in the wavelength region longer than 1240 nm.

[0022] The light absorbed by the SnSe layer 110 is not limited to near-infrared light. The SnSe layer 110 absorbs light such as visible light, which is light in a shorter wavelength range than near-infrared light. In other words, the SnSe layer 110 has light-receiving sensitivity to visible light as well.

[0023] The SnSe layer 110 generates electrons and holes as carriers in response to receiving near-infrared light and visible light. When the photoelectric conversion film 10 is applied to a photoelectric conversion element such as an imaging device, each of the electrons and holes generated in the SnSe layer 110 is extracted to the outside as an electric signal.

[0024] The thickness of the SnSe layer 110 is preferably 0.1 μm or more and 5.0 μm or less. The thickness of the SnSe layer 110 is more preferably 0.1 μm or more and 2.0 μm or less, and further preferably 0.3 μm or more and 2.0 μm or less. However, the thickness of the SnSe layer 110 is not limited to these values.

[0025] By setting the thickness of the SnSe layer 110 to 0.1 μm or more and 5.0 μm or less, more preferably 0.1 μm or more and 2.0 μm or less, and even more preferably 0.3 μm or more and 2.0 μm or less, it is possible to obtain a SnSe layer 110 that is excellent in productivity and that appropriately absorbs near-infrared light and visible light. That is, it is possible to obtain a SnSe layer 110 that has high light-receiving sensitivity to near-infrared light and visible light. In addition, since the thickness of the SnSe layer 110 is appropriately thin, the electric field intensity formed in the SnSe layer 110 can be increased even if the voltage value of the reverse bias voltage applied to the photoelectric conversion film 10 is low. As a result, it is possible to increase the extraction efficiency of electrons and holes generated in response to the absorption of near-infrared light.

[0026] On the other hand, when the thickness of the SnSe layer 110 is less than 0.1 μm, the SnSe layer 110 is too thin and may not be able to sufficiently absorb near-infrared light and visible light. When the thickness of the SnSe layer 110 exceeds 5.0 μm, the SnSe layer 110 is too thick and may hinder productivity. When the thickness of the SnSe layer 110 exceeds 5.0 μm, a large reverse bias voltage needs to be applied to the photoelectric conversion film 10 to form a desired electric field intensity in the SnSe layer 110. As a result, it may not be possible to reduce the power consumption when extracting the electrons and holes generated in the SnSe layer 110. Furthermore, in an imaging device including a plurality of photoelectric conversion films 10 arranged in the in-plane direction, if the thickness of the SnSe layer 110 exceeds 5.0 μm, the possibility of crosstalk occurring increases. The crosstalk here refers to a phenomenon in which incident light is incident across a plurality of pixels corresponding to each of the photoelectric conversion films 10, a light receiving signal is acquired from each of the plurality of pixels, and color mixing occurs between the pixels.

[0027] The photoelectric conversion film 10 may include, in addition to the SnSe layer 110, another photoelectric conversion layer that absorbs near-infrared light or visible light. Examples of materials constituting the other photoelectric conversion layer include silicon (Si) and selenium (Se). The other photoelectric conversion layer may be joined to the SnSe layer 110. The other photoelectric conversion layer may be formed by removing the Ga of the SnSe layer 110. 2 O 3 The SnSe layer 110 may face the surface of the Ga layer 120. 2 O 3 It may face the surface opposite to layer 120. The other photoelectric conversion layer may be disposed at a position other than the above.

[0028] Ga 2 O 3 The layer 120 is an n-type semiconductor layer that has a thickness in the direction perpendicular to the surface and extends in the in-plane direction. 2 O 3 The conductivity type of the layer 120 is not limited to this. 2 O 3 Layer 120 is bonded to SnSe layer 110 .

[0029] Ga 2 O 3 Ga in layer 120 2 O 3 is preferably a single crystal or a polycrystal. 2 O 3 Ga in layer 120 2 O 3 may be a non-crystalline substance such as an amorphous substance.

[0030] Single or polycrystalline Ga 2 O 3 has a band gap energy of about 4.9 eV. 2 O 3 Layer 120 has a much larger band gap energy than SnSe. 2 O 3 The layer 120 is Ga 2 O 3The GaAs layer 120 prevents holes from being injected into the SnSe layer 110 from a conductor such as an electrode that faces the SnSe layer 110 across the GaAs layer 120. 2 O 3 In the photoelectric conversion film 10, the layer 120 functions as a carrier block layer.

[0031] Ga 2 O 3 The thickness of the layer 120 is preferably 2 nm or more and 100 nm or less. 2 O 3 More preferably, the thickness of the layer 120 is greater than or equal to 2 nm and less than or equal to 50 nm.

[0032] Ga 2 O 3 By setting the thickness of the layer 120 to 2 nm or more and 100 nm or less, preferably 2 nm or more and 50 nm or less, productivity can be improved and a Ga 2 O 3 As a result, a Ga 2 O 3 The layer 120 can effectively block hole injection into the SnSe layer 110. 2 O 3 Since the layer 120 is a thin layer having a thickness of submicrometer or less, it is Ga 2 O 3 This reduces the electrical resistance of the layer 120. As a result, most of the reverse bias voltage applied to the photoelectric conversion film 10 is applied to the SnSe layer 110 side, and the extraction efficiency of electrons and holes generated in the SnSe layer 110 can be increased.

[0033] In contrast, Ga 2 O 3 When the thickness of layer 120 is less than 2 nm, Ga 2 O 3 Regions of the SnSe layer 110 that are not covered by the layer 120 may form. As a result, the Ga 2 O 3 Holes from a conductor such as an electrode can be injected into the SnSe layer 110 through the area not covered by the layer 120. 2 O3 Since the layer 120 is too thin, holes from the conductors such as electrodes enter the Ga 2 O 3 The probability of tunneling through the layer 120 and moving to the SnSe layer 110 side increases.

[0034] Also, Ga 2 O 3 When the thickness of the layer 120 is more than 100 nm, Ga 2 O 3 The layer 120 is too thick, which may hinder productivity. 2 O 3 When the thickness of the layer 120 is more than 100 nm, Ga 2 O 3 As a result of the increase in the electrical resistance of the layer 120, most of the reverse bias voltage applied to the photoelectric conversion film 10 is 2 O 3 The reverse bias voltage to the photoelectric conversion film 10 may be applied to the SnSe layer 110. That is, the reverse bias voltage to the photoelectric conversion film 10 may not be appropriately applied to the SnSe layer 110. As a result, the electric field strength formed in the SnSe layer 110 may be weak, and the extraction efficiency of the electrons and holes generated in the SnSe layer 110 may be reduced.

[0035] Ga 2 O 3 Layer 120 may include dopants. Ga 2 O 3 The dopant contained in the layer 120 may be a metal element such as tin (Sn). When the dopant is Sn, Ga 2 O 3 The content of Sn element in the layer 120 is Ga 2 O 3 It is preferable that the amount of the layer 120 is 10% or more and 40% or less of the total amount.

[0036] Ga 2 O 3 When the layer 120 contains 10% to 40% of Sn element, the dark current of the photoelectric conversion film 10 can be more effectively reduced. 2 O 3 The layer 120 contains 10% to 40% of Sn element, so that Ga2 O 3 This can reduce the electrical resistance of the layer 120. As a result, most of the reverse bias voltage applied to the photoelectric conversion film 10 is applied to the SnSe layer 110, and the efficiency of extracting electrons and holes generated in the SnSe layer 110 can be increased. Even if the voltage value of the reverse bias voltage is low, the efficiency of extracting electrons and holes generated in the SnSe layer 110 can be increased. As a result, power consumption can be reduced.

[0037] In contrast, Ga 2 O 3 When the content of Sn in the layer 120 is less than 10%, Ga 2 O 3 The electrical resistance of the layer 120 may not be sufficiently reduced. 2 O 3 When the content of Sn element in the layer 120 is more than 40%, Ga 2 O 3 Excess carriers can be generated in layer 120, increasing the dark current.

[0038] The photoelectric conversion film 10 is Ga 2 O 3 In addition to layer 120, other carrier blocking layers may be provided. Examples of materials constituting the other carrier blocking layers include semi-insulating semiconductors such as zinc oxide, zinc sulfide, cerium oxide, yttrium oxide, indium oxide, and titanium oxide. Here, "semi-insulating" refers to a material having a resistivity or conductivity close to that of an insulating material.

[0039] The other carrier block layer may be a hole block layer or an electron block layer. The other carrier block layer may be a Ga 2 O 3 In addition, other carrier blocking layers may be bonded to the layer 120. 2 O 3 The layer 120 may face the surface of the SnSe layer 110. 2 O 3It may be opposed to the surface of layer 120 opposite to SnSe layer 110. Other carrier blocking layers may be disposed in other locations.

[0040] The photoelectric conversion film 10 may be disposed on a substrate 20. As shown in Fig. 1, the substrate 20 is a flat member having a thickness in the direction perpendicular to the surface and extending in the in-plane direction.

[0041] Examples of the substrate 20 include a glass substrate, a quartz substrate, a sapphire substrate, an alumina substrate, a spinel substrate, a quartz substrate, a silicon substrate, a germanium substrate, a polyethylene substrate, a polyethylene terephthalate substrate, a polycarbonate substrate, etc. However, the type of the substrate 20 is not limited to these.

[0042] <<Manufacturing method>> Next, a method for manufacturing the photoelectric conversion film 10 according to this embodiment will be described with reference to Fig. 2. Fig. 2 is a schematic cross-sectional view for explaining each step in the method for manufacturing the photoelectric conversion film 10. Specifically, Fig. 2(a) shows a Ga 2 O 3 FIG. 2(b) is a cross-sectional view of the layer 120 cut along the XZ plane. 2 O 3 1 is a cross-sectional view of a photoelectric conversion film 10 in which a layer 120 and a SnSe layer 110 are laminated in this order, taken along the XZ plane.

[0043] The method for producing the photoelectric conversion film 10 according to this embodiment is to form a Ga 2 O 3 forming a layer 120; 2 O 3 forming a SnSe layer 110 on the layer 120.

[0044] As shown in FIG. 2(a), a Ga 2 O 3 The layer 120 is formed. 2 O 3The layer 120 can be formed by a dry process such as a vacuum deposition method, a pulsed laser deposition method, or a (high frequency) sputtering method, or a wet process such as an inkjet method, a spin coating method, or a dipping method. 2 O 3 The method for forming the layer 120 is not limited to the above.

[0045] Ga 2 O 3 It is preferable to control the thickness of layer 120 to 2 nm or more and 100 nm or less, and more preferably to 2 nm or more and 50 nm or less. For this reason, a high-frequency sputtering method is preferable, which can easily and precisely deposit a thin film (thin layer) having a thickness of submicrometer or less.

[0046] Ga 2 O 3 Dopants may be added to the layer 120. Ga 2 O 3 When forming the layer 120, Ga containing dopants are used. 2 O 3 By using a target, Ga 2 O 3 A dopant can be added to the layer 120. When the dopant is Sn, Ga 2 O 3 The Sn element is 10% to 40% of the total amount of the target. 2 O 3 It is preferable to include it in the target.

[0047] Ga 2 O 3 The method of adding dopants to the layer 120 is not limited to this. 2 O 3 Depending on the method of forming the layer 120, Ga 2 O 3 The method of adding the dopant to layer 120 may be selected as appropriate.

[0048] Next, as shown in Fig. 2(b), Ga 2 O 3The SnSe layer 110 is formed on the layer 120. Examples of methods for forming the SnSe layer 110 include dry processes such as vacuum deposition, pulsed laser deposition, and sputtering, and wet processes such as inkjet, spin coating, and dipping. However, the method for forming the SnSe layer 110 is not limited to these.

[0049] The photoelectric conversion film 10 is manufactured through the above steps. However, the method for manufacturing the photoelectric conversion film 10 may include steps other than the steps shown in FIG.

[0050] <<Example>> Specific examples of the above-described photoelectric conversion film 10 are described below. However, the present disclosure is not limited or restricted by the following examples.

[0051] In order to evaluate the light absorption characteristics of the photoelectric conversion film 10 from near infrared light to visible light, Example 1 was produced by the following method. Specifically, a 0.3 μm-thick SnSe layer 110 was formed on a substrate 20 by vacuum deposition to produce Example 1. Note that in order to evaluate the light absorption characteristics of the SnSe layer 110 that functions as a photoelectric conversion section, Example 1 was composed only of the SnSe layer 110 and did not include Ga 2 O 3 The layer 120 was not provided. In addition, the SnSe layer 110 of Example 1 was not subjected to a heat treatment.

[0052] Comparative Example 1 was produced as a comparison with Example 1. Similar to Example 1, Comparative Example 1 is composed only of a 0.3 μm thick SnSe layer formed on a substrate by vacuum deposition. The substrate used in Comparative Example 1 is similar to the substrate 20 in Example 1. Also, similar to Example 1, Comparative Example 1 is composed of a Ga 2 O 3 The layer 120 is not provided. Meanwhile, unlike Example 1, Comparative Example 1 was subjected to a heat treatment at 300° C. for 5 minutes.

[0053] As a method for evaluating the light absorption characteristics, Example 1 and Comparative Example 1 were each set in a spectrophotometer, and monochromatic light of wavelengths ranging from 400 nm to 900 nm was irradiated in order from the longest wavelength side, and the absorptance of Example 1 and Comparative Example 1 was measured.

[0054] The absorptance (λ) when monochromatic light of an arbitrary wavelength λ was incident was calculated using formula (1). "λ" corresponds to the wavelength of each monochromatic light incident sequentially on Example 1 and Comparative Example 1 in this measurement. Absorption rate (λ)={1-(transmitted light intensity T(λ) / incident light intensity I(λ))}×100 (1) Here, the incident light intensity I(λ) is the intensity of monochromatic light of wavelength λ incident on Example 1 and Comparative Example 1. The transmitted light intensity T(λ) is the intensity of light transmitted through Example 1 and Comparative Example 1 when monochromatic light of wavelength λ is incident on Example 1 and Comparative Example 1.

[0055] Fig. 3 shows the absorptance spectrum in Example 1 and Comparative Example 1. The solid line in Fig. 3 shows the absorptance spectrum in Example 1. The dashed line in Fig. 3 shows the absorptance spectrum in Comparative Example 1.

[0056] 3, Example 1 has a high absorptance of over 90% for light with wavelengths of 400 nm to 750 nm, which corresponds to the visible light region. Also, Example 1 has a high absorptance of over 60% for light with wavelengths of 750 nm to 900 nm, which corresponds to the near-infrared light region. In particular, the SnSe layer 110 of Example 1 has a high absorptance of about 75% for near-infrared light with a wavelength of 850 nm, despite being a thin layer with a thickness of 0.3 μm.

[0057] In contrast, the absorptance of Comparative Example 1 began to decrease as the wavelength of the incident light increased from about 600 nm in the visible light region. As a result, the absorptance of Comparative Example 1 for visible light with a wavelength of 750 nm decreased to about 40%. Furthermore, the absorptance of Comparative Example 1 for near-infrared light with a wavelength of 850 nm decreased to 20%.

[0058] In order to find the cause of the large difference in absorptance from the long wavelength side of the visible light region to the near infrared light region between Example 1 and Comparative Example 1, the compositions of Example 1 and Comparative Example 1 were evaluated. Specifically, the compositions of Example 1 and Comparative Example 1 were evaluated using an X-ray diffraction method.

[0059] The evaluation results are shown in Fig. 4. Fig. 4(a) shows the X-ray diffraction pattern in Example 1. Fig. 4(b) shows the X-ray diffraction pattern in Comparative Example 1.

[0060] As shown in Fig. 4(a), in Example 1, which was not subjected to heat treatment, only the diffraction peak of SnSe having monovalent selenium was confirmed. In contrast, as shown in Fig. 4(b), in Comparative Example 1, which was subjected to heat treatment, in addition to the diffraction peak of SnSe having monovalent selenium, the diffraction peak of SnSe having divalent selenium was confirmed. 2 The diffraction peak was confirmed.

[0061] SnSe 2 The band gap energy of SnSe is larger than that of SnSe. 2 Since it contains, the absorptance is reduced from the long wavelength side of the visible light region to the near infrared light region.

[0062] SnSe, while SnSe 2 It was confirmed that Example 1, which does not contain any of the above, has high light receiving sensitivity from the visible light region to the near infrared light region.

[0063] <<Action and effect>> According to this embodiment, the SnSe layer 110 has a high absorption rate of light in the visible light to near infrared light range, so that the light receiving sensitivity of visible light and near infrared light can be improved. 2 O 3 By providing the layer, carrier injection into the SnSe layer 110 can be effectively prevented, thereby reducing the dark current.

[0064] According to this embodiment, Ga 2 O 3 The layer 120 contains 10% to 40% of Sn element, so that Ga 2 O 3 This reduces the electrical resistance of the SnSe layer 120. As a result, most of the reverse bias voltage applied to the photoelectric conversion film 10 is applied to the SnSe layer 110, and the extraction efficiency of electrons and holes photoexcited in the SnSe layer 110 can be increased. 2 O 3 By setting the thickness of the layer to 2.0 nm or more and 100.0 nm or less, more preferably 2.0 nm or more and 50.0 nm or less, the productivity of the photoelectric conversion film 10 can be improved while 2 O 3 The electrical resistance of the layer 120 can be reduced. 2 O 3 By setting the layer thickness within this range, it is possible to increase the productivity and to increase the extraction efficiency of electrons and holes photoexcited in the SnSe layer 110.

[0065] According to this embodiment, by setting the thickness of the SnSe layer 110 to 0.1 μm or more and 5.0 μm or less, more preferably 0.1 μm or more and 2.0 μm or less, and even more preferably 0.3 μm or more and 2.0 μm or less, it is possible to form a strong electric field in the SnSe layer 110 even if a small reverse bias voltage is applied, while improving the productivity of the photoelectric conversion film 10. As a result, it is possible to increase the extraction efficiency of electrons and holes photoexcited in the SnSe layer 110.

[0066] According to this embodiment, the SnSe layer 110 is formed without heating. As a result, the SnSe-based compound contains SnSe, but 2 As a result, the SnSe layer 110 containing no SnSe can be obtained. As a result, the light receiving sensitivity to near-infrared light can be further improved.

[0067] According to this embodiment, Ga containing 10% to 40% Sn element is 2 O 3 The desired amount of Sn element is deposited on Ga by sputtering using a target. 2 O 3In other words, a high-quality Ga layer 120 having reduced electrical resistance can be obtained. 2 O 3 As a result of being able to easily fabricate the layer 120, it is possible to provide a method for manufacturing the photoelectric conversion film 10 that increases the extraction efficiency of electrons and holes photoexcited in the SnSe layer 110, has a high yield, and is excellent in productivity.

[0068] [Second embodiment] <Photoelectric conversion element> A photoelectric conversion element according to a second embodiment will be described.

[0069] <<Configuration>> An example of the configuration of a photoelectric conversion element 200 according to this embodiment will be described with reference to Fig. 5. Fig. 5 is a cross-sectional view of the photoelectric conversion element 200 cut along the XZ plane. As shown in Fig. 5, the photoelectric conversion element 200 includes a substrate 20, a lower electrode 30, a photoelectric conversion film 10, and an upper electrode 40. The lower electrode 30 corresponds to a "first electrode." The upper electrode 40 corresponds to a "second electrode."

[0070] The substrate 20, the lower electrode 30, the photoelectric conversion film 10, and the upper electrode 40 are stacked in this order from the lower side in the direction perpendicular to the surface. In the photoelectric conversion element 200, incident light may be incident from the substrate 20 side or from the upper electrode 40 side.

[0071] The substrate 20 is a member that serves as a base for the photoelectric conversion element 200. The configuration of the substrate 20 is similar to that of the substrate that supports the photoelectric conversion film 10 according to the first embodiment, and therefore a detailed description thereof will be omitted. When the incident light to the photoelectric conversion element 200 is incident from the substrate 20 side, the substrate 20 is made of a material that transmits visible light and near-infrared light, such as glass. On the other hand, when the incident light to the photoelectric conversion element 200 is incident from the upper electrode 40 side, the substrate 20 may be made of a material that absorbs visible light, such as Si.

[0072] 5, the lower electrode 30 is disposed on the substrate 20. When the photoelectric conversion element 200 is applied to an imaging device, the lower electrode 30 corresponds to a pixel electrode connected to a readout circuit included in the imaging device.

[0073] When the incident light to the photoelectric conversion element 200 is incident from the substrate 20 side, the lower electrode 30 is preferably a transparent electrode. Examples of materials constituting the transparent electrode include ITO (Tin-doped Indium Oxide) containing Sn element as a dopant, ATO (Antimony-doped Tin Oxide) containing antimony (Sb) element as a dopant, FTO (Fluorine-doped tin oxide) containing fluorine (F) element as a dopant, AZO (Aluminum-doped Zinc Oxide) containing aluminum (Al) element as a dopant, and GZO (Gallium-doped Zinc Oxide) containing gallium (Ga) element as a dopant.

[0074] In contrast, when incident light on the photoelectric conversion element 200 is incident from the upper electrode 40 side, the lower electrode 30 may be made of a metal such as aluminum (Al), gold (Au), titanium (Ti), niobium (Nb), copper (Cu), tungsten (W), molybdenum (Mo), etc.

[0075] The lower electrode 30 may be a mixture or a laminate of two or more of these materials, but the lower electrode 30 is not limited to these materials.

[0076] The photoelectric conversion film 10 is disposed on the lower electrode 30. As shown in FIG. 5, the photoelectric conversion film 10 includes a SnSe layer 110 and a Ga 2 O 3 and a layer 120. Note that the configuration of the photoelectric conversion film 10 is similar to that of the first embodiment, and therefore a detailed description thereof will be omitted.

[0077] 5, the upper electrode 40 is disposed on the photoelectric conversion film 10. When the photoelectric conversion element 200 is applied to an imaging device, the upper electrode 40 corresponds to an electrode called a counter electrode.

[0078] When incident light on the photoelectric conversion element 200 is incident from the substrate 20 side, the upper electrode 40 may be made of Al, Au, Ti, Nb, Cu, W, Mo, or the like.

[0079] On the other hand, when the incident light to the photoelectric conversion element 200 is incident from the upper electrode 40 side, it is preferable that the upper electrode 40 is a transparent electrode. Examples of materials constituting the transparent electrode include ITO, ATO, FTO, AZO, and GZO.

[0080] The upper electrode 40 may be a mixture or a laminate of two or more of these materials, but the upper electrode 40 is not limited to these materials.

[0081] The configuration of the photoelectric conversion element 200 has been described above. However, the configuration of the photoelectric conversion element 200 is not limited to that shown in Fig. 5. The photoelectric conversion element 200 may include other layers, such as a carrier block layer or a carrier transport layer, between the lower electrode 30 and the photoelectric conversion film 10. In addition, the photoelectric conversion element 200 may include other layers, such as a carrier block layer or a carrier transport layer, between the upper electrode 40 and the photoelectric conversion film 10.

[0082] <<Manufacturing method>> Next, a method for manufacturing the photoelectric conversion element 200 according to this embodiment will be described with reference to FIG. 6. FIG. 6 is a schematic cross-sectional view for explaining each step in the method for manufacturing the photoelectric conversion element 200. FIG. 6(a) is a cross-sectional view of a laminate 200A including a substrate 20 and a lower electrode 30 cut in an XZ plane. FIG. 6(b) is a cross-sectional view of a laminate 200B including a substrate 20, a lower electrode 30, and a photoelectric conversion film 10 cut in an XZ plane. FIG. 6(c) is a cross-sectional view of a photoelectric conversion element 200 including a substrate 20, a lower electrode 30, a photoelectric conversion film 10, and an upper electrode 40 cut in an XZ plane.

[0083] The manufacturing method of the photoelectric conversion element 200 of this embodiment includes the steps of forming a lower electrode 30 on a substrate 20, forming a photoelectric conversion film 10 on the lower electrode 30, and forming an upper electrode 40 on the photoelectric conversion film 10.

[0084] 6(a), a lower electrode 30 is formed on a substrate 20. Methods for forming the lower electrode 30 include dry processes such as vacuum deposition, pulsed laser deposition, and sputtering, and wet processes such as inkjet, spin coating, and dipping. However, the method for forming the lower electrode 30 is not limited to these.

[0085] 6(b), the photoelectric conversion film 10 is formed on the lower electrode 30. In forming the photoelectric conversion film 10, first, Ga 2 O 3 Then, a Ga layer 120 is formed. 2 O 3 The SnSe layer 110 is formed on the Ga layer 120. 2 O 3 The method for forming the layer 120 and the SnSe layer 110 may be a dry process such as a vacuum deposition method, a pulsed laser deposition method, or a sputtering method, or a wet process such as an inkjet method, a spin coating method, or a dipping method, as in the first embodiment. 2 O 3 As in the first embodiment, a dopant such as Sn element may be added to the layer 120. However, the method for forming the photoelectric conversion film 10 is not limited to these.

[0086] 6(c), the upper electrode 40 is formed on the photoelectric conversion film 10. Examples of methods for forming the upper electrode 40 include dry processes such as vacuum deposition, pulsed laser deposition, and sputtering, and wet processes such as inkjet, spin coating, and dipping. However, the method for forming the upper electrode 40 is not limited to these.

[0087] The photoelectric conversion element 200 is manufactured through the above steps. However, the method for manufacturing the photoelectric conversion element 200 may include steps other than the steps shown in FIG.

[0088] <<Example>> Specific examples of the above-described photoelectric conversion element 200 will be described below. However, the present disclosure is not limited or restricted by the following examples.

[0089] Example 2 was produced in order to evaluate the current-voltage characteristics (dark current characteristics) in the dark of the photoelectric conversion element 200. Example 2 was produced using a glass substrate as the substrate 20, a lower ITO electrode as the lower electrode 30, and a SnSe layer 110 and a Ga 2 O 3 The photoelectric conversion film 10 includes a layer 120, and an upper ITO electrode as an upper electrode 40.

[0090] Example 2 was produced by the following method: First, a lower ITO electrode was formed on a glass substrate by sputtering.

[0091] Next, Ga was deposited on the lower ITO electrode using a high-frequency sputtering method. 2 O 3 Specifically, the oxygen partial pressure in the chamber was set to 1.5×10 -2 After adjusting to Pa, 2 O 3 An AC voltage (high frequency power: 100 W) was applied between the conductor connected to the target and another conductor connected to the lower ITO electrode. 2 O 3 The layer 120 was evaporated. 2 O 3 The target used was one containing 40% Sn element.

[0092] Next, a 0.3 μm thick SnSe layer 110 is formed on the Ga 2 O 3 The SnSe layer 110 was formed on the SnSe layer 120. However, the SnSe layer 110 was not subjected to a heat treatment. 2 Thus, the SnSe layer 110 containing no Ga was formed. 2 O 3 The layer 120 and the SnSe layer 110 were laminated in this order to form the photoelectric conversion film 10.

[0093] Subsequently, a sputtering method was used to form an upper ITO electrode on the photoelectric conversion film 10. Through the above steps, Example 2 was produced.

[0094] Comparative Example 2 was prepared as a comparison with Example 2. 2 O 3 Except for not including the layer 120, the comparative example 2 has the same configuration as the example 1. That is, the comparative example 2 includes a glass substrate, a lower ITO electrode, a SnSe layer 110, and an upper ITO electrode.

[0095] FIG. 7 shows the dark current characteristics of Example 2 and Comparative Example 2. Here, the horizontal axis of FIG. 7 shows the voltage values ​​of the bias voltage applied to Example 2 and Comparative Example 2. The + side of the horizontal axis of FIG. 7 corresponds to the voltage value of the reverse bias voltage. The - side of the horizontal axis of FIG. 7 corresponds to the voltage value of the forward bias voltage. The vertical axis of FIG. 7 shows the current values ​​of Example 2 and Comparative Example 2 at each voltage value of the applied bias voltage. The solid line in FIG. 7 shows the dark current characteristics of Example 2. Also, the dashed line in FIG. 7 shows the dark current characteristics in Comparative Example 2.

[0096] 7, the dark current of Example 2 was significantly reduced compared to the dark current of Comparative Example 2. Specifically, the current of Example 2 when a reverse bias voltage of 0.5 V was applied was about 0.04 μA, whereas the current of Comparative Example 2 when a reverse bias voltage of 0.5 V was applied was about 0.9 μA. That is, the dark current of Example 2 was reduced to about 1 / 25 of the dark current of Comparative Example 2.

[0097] From the above, the SnSe layer 110 and Ga 2 O 3 It was confirmed that the junction structure between the SnSe layer 110 and the Ga layer 120 can also effectively prevent hole injection from the electrode. 2 O 3 By using the photoelectric conversion film 10 including the layer 120, a photoelectric conversion element 200 was obtained that has high light receiving sensitivity from visible light to near infrared light and can reduce dark current.

[0098] <<Action and effect>> According to this embodiment, the SnSe layer 110 has a high absorption rate of light in the visible light to near infrared light range, so that the light receiving sensitivity of visible light and near infrared light can be improved. 2 O 3 By providing the layer, carrier injection from the lower electrode 30 to the SnSe layer 110 can be effectively prevented, and as a result, the dark current can be reduced.

[0099] According to this embodiment, Ga containing 10% to 40% Sn element is 2 O 3 The desired amount of Sn element is deposited on Ga by sputtering using a target. 2 O 3 In other words, a high-quality Ga layer 120 having reduced electrical resistance can be obtained. 2 O 3 As a result of being able to easily fabricate the layer 120, it is possible to provide a method for manufacturing the photoelectric conversion element 200 that increases the extraction efficiency of electrons and holes photoexcited in the SnSe layer 110, has a high yield, and is excellent in productivity.

[0100] [Example of application] The photoelectric conversion element 200 according to the embodiment can be applied to an imaging device that converts incident light from an object to be imaged into an electrical signal, etc. The imaging device further includes a readout circuit that reads out the electrical signal obtained by the photoelectric conversion element 200.

[0101] Although the embodiments have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications and improvements are possible within the scope of the present disclosure. [Explanation of symbols]

[0102] 10 Photoelectric conversion film 110 SnSe layer 120 Ga 2 O 3 layer 20 Substrate 30 Lower electrode 40 Upper electrode 200 Photoelectric conversion element

Claims

1. G ２ O ３ Layers, The Ga ２ O ３ a SnSe layer disposed on the layer; and A photoelectric conversion film comprising:

2. The Ga ２ O ３ The photoelectric conversion film according to claim 1 , wherein the layer contains 10% to 40% of Sn element.

3. The photoelectric conversion film according to claim 1 or 2, wherein the SnSe layer has a thickness of 0.1 μm or more and 5.0 μm or less.

4. The Ga ２ O ３ The photoelectric conversion film according to claim 1 or 2, wherein the layer has a thickness of 2.0 nm or more and 100.0 nm or less.

5. The SnSe layer contains SnSe, while SnSe ２ The photoelectric conversion film according to claim 1 or 2, which does not contain

6. A first electrode; Ga disposed on the first electrode ２ O ３ Layers, G ２ O ３ a SnSe layer disposed on the layer; and a second electrode disposed on the SnSe layer; A photoelectric conversion element comprising:

7. Ga containing 10% to 40% Sn element ２ O ３ The Ga was deposited on the substrate by sputtering using a target. ２ O ３ forming a layer; The Ga ２ O ３ forming a SnSe layer on the layer; The method for producing a photoelectric conversion film includes the steps of:

8. forming a first electrode; Ga containing 10% to 40% Sn element ２ O ３ A sputtering method using a target is used to deposit Ga on the first electrode. ２ O ３ forming a layer; The Ga ２ O ３ forming a SnSe layer on the layer; forming a second electrode on the SnSe layer; A method for producing a photoelectric conversion element comprising the steps of:

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