Photoelectric conversion element

Abstract

Devices using III-V compound semiconductors utilize single-crystal substrates for crystal growth. [Solution] The photoelectric conversion element comprises an amorphous substrate, an orientation control layer on the amorphous substrate, and a photoelectric conversion structure on the orientation control layer. The photoelectric conversion structure is formed of a crystalline III-V compound semiconductor and has a pn junction or pin structure. The band gap of the crystalline III-V compound semiconductor is 1.24 eV or less, and the orientation control layer has c-axis oriented crystals.

Description

[Technical Field]

[0001] One embodiment of the present invention relates to the structure of a photoelectric conversion element in which a photoelectric conversion structure is formed from a compound semiconductor. [Background technology]

[0002] An infrared sensor, which is a photoelectric conversion element, is disclosed in which an n-type semiconductor layer, an i-type semiconductor layer, and a p-type semiconductor layer made of III-V compound semiconductors are stacked on a GaAs substrate (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2014-072217 [Overview of the project] [Problems that the invention aims to solve]

[0004] For photoelectric conversion, such as detecting infrared radiation, III-V compound semiconductors are suitable from the perspective of band gap. III-V compound semiconductors are fabricated by molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD), and single-crystal substrates are used for crystal growth. Single-crystal silicon and sapphire substrates are expensive, which is a factor in the high cost of infrared sensors, which are photoelectric conversion elements. [Means for solving the problem]

[0005] A photoelectric conversion element according to one embodiment of the present invention comprises an amorphous substrate, an orientation control layer on the amorphous substrate, and a photoelectric conversion structure on the orientation control layer, wherein the photoelectric conversion structure is formed of a crystalline III-V compound semiconductor. [Brief explanation of the drawing]

[0006] [Figure 1] This is a cross-sectional view showing the structure of a photoelectric conversion element according to one embodiment of the present invention. [Figure 2A] This is a cross-sectional view showing the structure of a photoelectric conversion element according to one embodiment of the present invention. [Figure 2B] This is a cross-sectional view showing the structure of a photoelectric conversion element according to one embodiment of the present invention. [Figure 3] This is a cross-sectional view showing the structure of a photoelectric conversion element according to one embodiment of the present invention. [Figure 4] This is a cross-sectional view showing the structure of a photoelectric conversion element according to one embodiment of the present invention. [Figure 5] This is a cross-sectional view showing the structure of a photoelectric conversion element according to one embodiment of the present invention. [Figure 6] This is a cross-sectional view showing the structure of a photoelectric conversion element according to one embodiment of the present invention. [Figure 7] This is a cross-sectional view showing the structure of a photoelectric conversion element according to one embodiment of the present invention. [Modes for carrying out the invention]

[0007] Embodiments of the present invention will be described with reference to the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described below. In order to make the explanation clearer, the drawings may schematically represent the width, thickness, shape, etc. of each part compared to the actual embodiment, but these are merely examples and do not limit the interpretation of the present invention. In addition, in this specification and each drawing, elements similar to those described above with respect to previously shown drawings are denoted by the same reference numerals (or numerals followed by A, B, etc.), and detailed explanations may be omitted as appropriate. Furthermore, the letters "1st," "2nd," etc., attached to each element are convenient indicators used to distinguish each element and have no further meaning unless specifically explained.

[0008] In this specification, when a member or region is said to be "above (or below)" another member or region, unless otherwise specified, this includes not only cases where it is directly above (or directly below) the other member or region, but also cases where it is above (or below) the other member or region, that is, cases where another component is included between them above (or below) the other member or region.

[0009] In this specification, a photoelectric conversion structure refers to a structure or laminate that converts light energy into electrical energy, and for example, refers to a layer containing one of the following structures known as semiconductor junction structures: a pn junction, a PIN structure, or a Schottky junction.

[0010] In this specification, "substantially intrinsic" is not limited to cases where the semiconductor is evaluated as an intrinsic semiconductor free of conductivity type impurities, but refers to a state close to an intrinsic semiconductor free of impurities that control conductivity type, and may contain trace amounts of impurities that impart n-type or p-type to the extent that it can function as an intrinsic semiconductor, and may also include cases where such trace amounts of impurities result in a semiconductor being called weakly n-type or weakly p-type. In other words, "substantially intrinsic" means that the carrier density is 1 × 10⁻⁶. 18 / cm 3 Less than 1 × 10 15 / cm 3 This refers to being less than a certain value. In the following explanation, when a compound semiconductor layer is intrinsic or substantially intrinsic, it may be referred to as type i to distinguish it from type n and type p.

[0011] The configuration of the photoelectric conversion element according to one embodiment of the present invention will be described below with reference to the drawings. The photoelectric conversion element according to one embodiment of the present invention includes one that is sensitive to the infrared wavelength region.

[0012] [First Embodiment] FIG. 1 shows a cross-sectional view of a photoelectric conversion element 100 according to the present embodiment. The photoelectric conversion element 100 includes an alignment control layer 104 provided on an amorphous substrate 102 and a photoelectric conversion structure 106 provided on the alignment control layer 104. An underlying insulating layer 103 may be provided between the amorphous substrate 102 and the alignment control layer 104. Also, a first electrode 107 and a second electrode 108 are provided so as to contact the photoelectric conversion structure 106. FIG. 1 shows a structure in which the alignment control layer 104 also serves as the first electrode 107 and the second electrode 108 is provided on the photoelectric conversion structure 106. The first electrode 107 and the second electrode 108 are in ohmic contact with the photoelectric conversion structure 106. Although not shown in FIG. 1, a passivation layer may be provided so as to cover the photoelectric conversion structure 106.

[0013] The photoelectric conversion structure 106 is formed of a III-V compound semiconductor (hereinafter, simply referred to as a "compound semiconductor" unless otherwise specified). FIG. 1 shows a structure in which the photoelectric conversion structure 106 is formed of a first compound semiconductor layer 1062, a second compound semiconductor layer 1064, and a third compound semiconductor layer 1066. The first compound semiconductor layer 1062, the second compound semiconductor layer 1064, and the third compound semiconductor layer 1066 are laminated in this order from the side of the amorphous substrate 102.

[0014] The first compound semiconductor layer 1062 has one conductivity type, the second compound semiconductor layer 1064 is intrinsic or substantially intrinsic, and the third compound semiconductor layer 1066 has a conductivity type opposite to the one conductivity type. For example, the conductivity type of the first compound semiconductor layer 1062 is n-type, and the conductivity type of the third compound semiconductor layer 1066 is p-type. Also, the first compound semiconductor layer 1062 may have a p-type conductivity type, and the third compound semiconductor layer 1066 may have an n-type conductivity type. The photoelectric conversion structure 106 shown in FIG. 1 has a structure of a pin diode in which the first compound semiconductor layer 1062, the second compound semiconductor layer 1064, and the third compound semiconductor layer 1066 having such conductivity types are laminated.

[0015] The photoelectric conversion element 100 operates when a bias voltage (reverse bias) is applied between the first electrode 107 and the second electrode 108. When infrared light is incident on the photoelectric conversion element 100, photoelectric conversion occurs in the second compound semiconductor layer 1064, generating electrons and holes. Due to the influence of the applied bias voltage and the internal electric field, electrons drift towards the first electrode 107 and holes drift towards the second electrode 108. In a simple circuit configuration, if a load (resistor R) is connected between the first electrode 107 and the second electrode 108, a current I flows. The photoelectric conversion element 100, having a pin structure, has a small dark current (current in the absence of light irradiation) and can achieve a high response speed.

[0016] Note that the photoelectric conversion structure 106 is not limited to the structure shown in Figure 1. The photoelectric conversion structure 106 may have a pn junction diode structure in which a first compound semiconductor layer 1062 of one conductivity type and a third compound semiconductor layer 1066 of the opposite conductivity type are stacked, as shown in Figure 2A. Also, as shown in Figure 2B, the photoelectric conversion structure 106 may consist of a first compound semiconductor layer 1062 (n type), a p-type compound semiconductor layer 1063, and p - The avalanche photodiode structure may have a p-type compound semiconductor layer 1065 and a third compound semiconductor layer 1066 (p-type) stacked on top of each other. In this case, the p-type compound semiconductor layer 1063 functions as an electron accelerating layer, and p - The compound semiconductor layer 1065 functions as a light absorption layer. Photoelectric conversion element 100 having such a junction structure has an amplification function, can detect weak light with high sensitivity, and can achieve a high response speed.

[0017] While the amorphous substrate 102 is non-crystalline, each compound semiconductor layer constituting the photoelectric conversion structure 106 is crystalline. The orientation control layer 104 is interposed between the amorphous substrate 102 and the photoelectric conversion structure 106 and is provided to improve the crystallinity of each compound semiconductor layer constituting the photoelectric conversion structure 106.

[0018] The light-receiving surface of the photoelectric conversion element 100 can be the upper side of the photoelectric conversion structure 106 (the side of the third compound semiconductor layer 1066). Alternatively, if the amorphous substrate 102 and the orientation control layer 104 are transparent to the wavelength of infrared light (i.e., they transmit infrared light), the light-receiving surface can be the lower side of the photoelectric conversion structure 106 (the side of the first compound semiconductor layer 1062).

[0019] As described above, the photoelectric conversion element 100 according to this embodiment has a structure in which a photoelectric conversion structure 106 formed of a compound semiconductor layer is provided on an amorphous substrate 102. The details of each component constituting the photoelectric conversion element 100 will be described below.

[0020] (1) Amorphous substrate The amorphous substrate 102 does not have a crystalline structure and has a thermal expansion coefficient of 50 × 10 -7 A substrate with a temperature less than / ℃ and a strain point of 600℃ or higher is used. A glass substrate can be used as the amorphous substrate 102 that satisfies these characteristics. There are various types of glass substrates, but for example, a glass substrate made of aluminoborosilicate glass or a glass substrate made of aluminosilicate glass can be used. Preferably, the glass substrate has an alkali metal content of 0.1% or less, such as sodium (Na). Such glass substrates are used in liquid crystal displays and organic electroluminescent (organic EL) displays, and large-area glass substrates called mother glass are available on the market. By using such a glass substrate as the amorphous substrate 102, it is possible to increase the area and improve the productivity of the photoelectric conversion element 100.

[0021] In addition to glass substrates, flexible resin substrates such as polyimide substrates, acrylic substrates, siloxane substrates, and fluororesin substrates can also be used as amorphous substrates 102.

[0022] (2) Substrate insulating layer As shown in Figure 1, an additional underlayer insulating layer 103 may be provided on the amorphous substrate 102. The underlayer insulating layer 103 has a single-layer structure of an inorganic insulating film, or a structure in which multiple inorganic insulating films are laminated. As the inorganic insulating film, for example, silicon nitride film, silicon oxide film, silicon oxynitride film, aluminum nitride film, aluminum oxide film, and aluminum oxynitride film can be used. For example, the underlayer insulating layer 103 may have a structure in which a silicon nitride film and a silicon oxide film are laminated in order from the amorphous substrate 102 side. Preferably, the silicon nitride film of the underlayer insulating layer 103 has a film thickness of, for example, 20 nm to 500 nm, and the silicon oxide film has a film thickness of, for example, 20 nm to 500 nm.

[0023] When a glass substrate is used as the amorphous substrate 102, the glass substrate contains trace amounts of alkali metals (such as sodium). Therefore, contamination of the photoelectric conversion structure 106 by alkali metals becomes a problem. To address this problem, providing an underlying insulating layer 103 prevents the diffusion of alkali metals from the amorphous substrate 102 and thus prevents contamination of the photoelectric conversion structure 106. A silicon nitride film used as the underlying insulating layer 103 can block alkali metals if it has a thickness of 20 nm or more.

[0024] Furthermore, the underlying insulating layer 103 can improve the adhesion of the orientation control layer 104. In other words, it is possible to prevent the orientation control layer 104 from peeling off from the amorphous substrate 102. For example, by providing a silicon oxide film with a thickness of 20 nm or more as the underlying insulating layer 103, peeling of the orientation control layer 104 can be prevented.

[0025] In this way, the underlying insulating layer 103 can combine the function of a barrier layer against impurities with the function of improving the adhesion of the orientation control layer 104.

[0026] (3) Orientation control layer The orientation control layer 104 is provided to improve the crystallinity of the photoelectric conversion structure 106. While the amorphous substrate 102 does not have crystallinity, the orientation control layer 104 does.

[0027] The orientation control layer 104 can be selected from conductive materials and insulating materials. In the photoelectric conversion element 100 shown in Figure 1, the orientation control layer 104 also serves as the first electrode 107, so it is selected from conductive materials. The orientation control layer 104 is also selected from materials that are easy to lattice match with the compound semiconductor material forming the photoelectric conversion structure 106. As will be described later, the photoelectric conversion structure 106 is formed of a compound semiconductor that has photosensitivity in the infrared wavelength band. Having photosensitivity means that when a compound semiconductor film formed of the compound semiconductor material is irradiated with light of the above predetermined wavelength, photoconductivity is observed. In order to achieve lattice matching with such a compound semiconductor, it is preferable that the orientation control layer 104 has a lattice constant (value of a) in the range of 0.56 nm to 0.60 nm.

[0028] If the compound semiconductor layer forming the photoelectric conversion structure 106 has c-axis oriented crystallinity, it is preferable that the orientation control layer 104 is also c-axis oriented. The crystal of the orientation control layer 104 preferably has rotational symmetry; for example, it is preferable that its crystal surface has six-fold symmetry. The crystal structure of the orientation control layer 104 preferably has a hexagonal close-packed structure, a face-centered cubic structure, or a structure similar thereto. A hexagonal close-packed structure or a structure similar to a face-centered cubic structure includes a crystal structure in which the c axis is not 90 degrees with respect to the a axis and b axis. An orientation control layer 104 having a hexagonal close-packed structure or a structure similar thereto is preferably oriented in the (0001) direction, i.e., in the c-axis direction, with respect to the surface of the amorphous substrate 102 (this orientation state is also called the (0001) orientation of the hexagonal close-packed structure). Furthermore, the orientation control layer 104 having a face-centered cubic structure or a similar structure is preferably oriented in the (111) direction with respect to the surface of the amorphous substrate 102 (this orientation state is also called the (111) orientation of the face-centered cubic structure).

[0029] The orientation control layer 104 preferably has high surface flatness. When the flatness of the orientation control layer 104 is expressed in terms of arithmetic mean roughness (Ra), Ra is preferably less than 2.5 nm, and more preferably less than 2.3 nm. The arithmetic mean roughness (Ra) is a value measured by an atomic force microscope (AFM). By having a flat surface of the orientation control layer 104, the crystallinity of the compound semiconductor layer forming the photoelectric conversion structure 106 can be improved.

[0030] The thickness of the orientation control layer 104 is preferably 5 nm to 500 nm, and more preferably 10 nm to 200 nm, in order to improve flatness. The thickness can be measured using a contact step meter, an optical thickness meter (ellipsometry), or from images obtained with a scanning electron microscope (SEM) or transmission electron microscope (TEM). Having the orientation control layer 104 within this thickness range improves the surface flatness and enhances the crystallinity of the compound semiconductor layer forming the photoelectric conversion structure 106.

[0031] The orientation control layer 104 can be formed from a variety of materials. As the orientation control layer 104, crystals of silicon (Si), germanium (Ge), antimony (Sb), and mixed crystals composed of two or more of these elements can be used. Furthermore, aluminum nitride (AlN), gallium nitride (GaN), indium nitride (InN), and mixed crystals of these materials can be used. Additionally, zirconium (Zr), scandium (Sc), hafnium (Hf), magnesium (Mg), and zinc oxide (ZnO) can be used as the orientation control layer 104. Moreover, graphene, nickel (Ni), and titanium (Ti) can be used as the orientation control layer 104.

[0032] The orientation control layer 104 may be a single layer or may have a structure in which multiple layers are stacked. The orientation control layer 104 can be fabricated on the amorphous substrate 102, for example, by sputtering or vacuum deposition. Alternatively, the orientation control layer 104 may be fabricated by chemical vapor deposition (CVD) or atomic layer deposition (ALD).

[0033] (3) Photoelectric conversion structure The photoelectric conversion structure 106 is formed from a compound semiconductor material that is photosensitive to infrared light with a wavelength of 0.75 μm or more, preferably 1.0 μm or more, more preferably 1.3 μm or more, and even more preferably 1.6 μm or more. In other words, the compound semiconductor forming the photoelectric conversion structure 106 preferably has a band gap of 1.66 eV or less, preferably 1.24 eV or less, more preferably 0.95 eV or less, and even more preferably 0.78 eV or less, and is photosensitive to infrared light.

[0034] As shown in Figure 1, when the photoelectric conversion structure 106 has a structure in which a first compound semiconductor layer 1062 (n-type), a second compound semiconductor layer 1064 (i-type), and a third compound semiconductor layer 1066 (p-type) are stacked, it is preferable that at least the second compound semiconductor layer 1064 is photosensitive to infrared light.

[0035] The compound semiconductor forming the photoelectric conversion structure 106 is preferably lattice-matched with the orientation control layer from the viewpoint of eliminating lattice mismatch. As shown in Figure 1, when the photoelectric conversion structure 106 has a structure in which a first compound semiconductor layer 1062 (n-type), a second compound semiconductor layer 1064 (i-type), and a third compound semiconductor layer 1066 (p-type) are stacked, it is preferable that at least the first compound semiconductor layer 1062 is lattice-matched with the orientation control layer. By having the crystallinity of the first compound semiconductor layer 1062 formed as the first layer on the orientation control layer 104, the second compound semiconductor layer 1064 and the third compound semiconductor layer 1066 formed thereon can also be made crystallinity.

[0036] As III-V compound semiconductor materials, aluminum (Al), gallium (Ga), and indium (In) from Group 13 of the periodic table, and nitrogen (N), phosphorus (P), arsenic (As), and antimony (Sb) from Group 15 of the periodic table can be used. Examples of III-V compound semiconductors composed of these elements include InGaAs, InAsN, InAsP, InGaN, GaAsP, InAsN, GaAsSb, and InN. By controlling the elemental composition ratio, the band gap of these III-V compound semiconductors can be made 1.66 eV or less, preferably 1.24 eV or less, more preferably 0.95 eV or less, and even more preferably 0.78 eV or less. The orientation control layer 104 is preferably formed by appropriately selecting materials such as those exemplified above so as to be lattice-matched with such III-V compound semiconductors.

[0037] The valence electron configuration of III-V compound semiconductors can be controlled to either n-type or p-type by adding dopants. For n-type dopants, one or more elements selected from silicon (Si) or germanium (Ge) are used, for example. For p-type dopants, one or more elements selected from magnesium (Mg), zinc (Zn), cadmium (Cd), and beryllium (Be) are used, for example.

[0038] In this embodiment, the photoelectric conversion structure 106 (first compound semiconductor layer 1062, second compound semiconductor layer 1064, third compound semiconductor layer 1066) is fabricated, for example, by sputtering. The substrate temperature (set temperature) during sputtering is controlled to be in the range of 100°C to 650°C. Since an orientation control layer 104 is provided on the substrate of the first compound semiconductor layer 1062 formed as the first layer, heteroepitaxial growth can be achieved even when the substrate temperature is below 650°C, and crystallization can be promoted.

[0039] The sputtering target mounted on the sputtering apparatus is appropriately selected according to the composition of the compound semiconductor layer to be deposited. For example, a sintered body of a III-V compound semiconductor is used as the sputtering target. The first compound semiconductor layer 1062, the second compound semiconductor layer 1064, and the third compound semiconductor layer 1066 may be formed from III-V compound semiconductors of the same composition, or they may be formed from mutually different III-V compound semiconductors. Since the first compound semiconductor layer 1062 and the third compound semiconductor layer 1066 have different dopants, it is preferable to fabricate each layer using different sputtering targets. In the structure of the photoelectric conversion structure 106 shown in Figure 1, it is preferable that the band gap of the first compound semiconductor layer 1062 or the third compound semiconductor layer 1066, which is located on the light-receiving surface side, is larger than the band gap of the second compound semiconductor layer 1064. This configuration makes it possible to reduce the light absorption loss caused by the first compound semiconductor layer 1062 or the third compound semiconductor layer 1066 located on the light-receiving surface side, thereby improving the sensitivity of the photoelectric conversion element 100.

[0040] For sputtering film deposition, argon (Ar) or a mixture of argon (Ar) and nitrogen (N2) is used as the sputtering gas. Sputtering equipment can include two-pole sputtering systems, magnetron sputtering systems, dual magnetron sputtering systems, opposing target sputtering systems, ion beam sputtering systems, and inductively coupled plasma (ICP) sputtering systems.

[0041] There are no limitations on the film thickness of the first compound semiconductor layer 1062, the second compound semiconductor layer 1064, and the third compound semiconductor layer 1066. The first compound semiconductor layer 1062, the second compound semiconductor layer 1064, and the third compound semiconductor layer 1066 only need to have a film thickness that can form a PIN structure. In the photoelectric conversion structure 106, the second compound semiconductor layer 1064 is mainly responsible for absorbing infrared rays. Therefore, it is preferable that the second compound semiconductor layer 1064 has a film thickness of 500 nm to 15000 nm in order to absorb infrared rays.

[0042] (4) First electrode and second electrode The photoelectric conversion element 100 shown in Figure 1 has a second electrode 108 provided on a third compound semiconductor layer 1066. The second electrode 108 can be made of a metallic material that makes ohmic contact with the third compound semiconductor layer 1066, or it can be formed using a different metallic material. If the third compound semiconductor layer 1066 is p-type, the second electrode 108 may be made of, for example, gold (Au) or an alloy of gold (Au), and as an alloy of gold (Au), a gold-zinc (AuZn) alloy or a gold-antimony (Au-Sb) alloy may be used.

[0043] In the photoelectric conversion element 100 shown in Figure 1, the orientation control layer 104 also serves as the first electrode 107. Therefore, the orientation control layer 104 can be made of a conductive material capable of forming ohmic contact with the first compound semiconductor layer 1062, or it can be made of other conductive materials. The orientation control layer 104, which also serves as the first electrode 107, may be made of, for example, nickel (Ni), titanium (Ti), zinc oxide (ZnO), etc.

[0044] The photoelectric conversion element 100 according to this embodiment has a structure in which a photoelectric conversion structure 106 is provided on an amorphous substrate 102. The photoelectric conversion structure 106 is formed of a III-V compound semiconductor and can have photosensitivity in the infrared wavelength band, and can be used as an infrared sensor. Because the photoelectric conversion structure 106 is formed of a crystalline III-V compound semiconductor, a photoelectric conversion element 100 with high sensitivity and low noise can be provided. Furthermore, the amorphous substrate 102 is less expensive than a single-crystal substrate such as a sapphire substrate and can be made in a large area, so the productivity of the photoelectric conversion element 100 can be improved and costs can be reduced.

[0045] [Second Embodiment] Figure 3 shows a cross-sectional view of the photoelectric conversion element 100 according to this embodiment. The photoelectric conversion element 100 according to this embodiment differs from the configuration shown in the first embodiment in the configuration of the first electrode 107. In the following description, the differences from the first embodiment will be the focus of the explanation, and common parts will be omitted as appropriate.

[0046] The photoelectric conversion element 100 shown in Figure 3 has a structure in which a part of the photoelectric conversion structure 106 is etched. Specifically, within the photoelectric conversion structure 106, a region is provided in which a part of the third compound semiconductor layer 1066 and the second compound semiconductor layer 1064 is removed, exposing the first compound semiconductor layer 1062. A first electrode 107 is provided in the region in which the first compound semiconductor layer 1062 is exposed. The first electrode 107 is formed of a material that makes ohmic contact with the first compound semiconductor layer 1062. The first electrode 107 is formed of, for example, a metallic material such as titanium (Ti) or gold (Au), or a metal oxide material such as zinc oxide (ZnO). The first electrode 107 may also have a structure in which multiple conductive materials are stacked, in which case it is preferable that the layer in contact with the first compound semiconductor layer 1062 uses the above-mentioned metallic material or metal oxide material.

[0047] The orientation control layer 104 may be formed from a conductive material or an insulating material. For example, the orientation control layer 104 can be formed from aluminum nitride (AlN). Since aluminum nitride is transparent to infrared rays, the amorphous substrate 102 side can be used as the light-receiving surface.

[0048] The photoelectric conversion element 100 according to this embodiment is the same as the photoelectric conversion element in the first embodiment, except for the configuration of the first electrode 107, and can achieve the same effects. Since the first electrode 107 and the second electrode 108 are provided on the same surface (the surface on the photoelectric conversion structure side) of the photoelectric conversion element 100 according to this embodiment, it is suitable for surface mounting.

[0049] [Third Embodiment] FIG. 4 shows a cross-sectional view of the photoelectric conversion element 100 according to the present embodiment. The photoelectric conversion element 100 according to the present embodiment has a structure in which a high-resistance layer 110 is further inserted between the orientation control layer 104 and the photoelectric conversion structure 106 with respect to the structure shown in the second embodiment. In the following description, the description will focus on the differences from the second embodiment, and the common parts will be omitted as appropriate.

[0050] The high-resistance layer 110 preferably has a lattice constant similar to that of the orientation control layer 104. That is, the lattice constant (value of a) of the high-resistance layer 110 is preferably in the range of 0.56 nm to 0.60 nm. Although there is no limitation on the resistivity of the high-resistance layer 110, it is 1×10 6 Ωcm, preferably having a resistivity of 1×10 7 Ωcm. By having such a resistivity for the high-resistance layer 110, even when the orientation control layer 104 has conductivity, the photoelectric conversion structure 106 can be insulated from the orientation control layer 104.

[0051] Indium phosphide (InP) can be used as the high-resistance layer 110. It is preferable that impurities such as iron (Fe), silicon (Si), sulfur (S), and zinc (Zn) are added to the indium phosphide (InP) used as the high-resistance layer 110, and by adding such impurities, the resistance can be increased.

[0052] Indium phosphide (InP) is a type of III-V compound semiconductor, but since its bandgap is about 1.35 eV, it is not suitable for use as a photoelectric conversion structure of an infrared sensor. However, since the lattice constant of indium phosphide (InP) is 0.5869 nm, it is suitable for lattice matching with a material such as InGaAs used as the photoelectric conversion structure 106, and the crystallinity can be improved.

[0053] In this embodiment, the photoelectric conversion element 100 has a high-resistance layer 110 between the orientation control layer 104 and the photoelectric conversion structure 106, which allows the photoelectric conversion structure 106 to be insulated from the orientation control layer 104 even when the orientation control layer 104 is conductive. Furthermore, by using a high-resistance layer 110 with a lattice constant in the range of 0.56 nm to 0.60 nm, the crystallinity of the photoelectric conversion structure 106 can be improved without being affected by the state of the orientation control layer 104. The photoelectric conversion element 100 in this embodiment has the same configuration as the second embodiment except for the provision of the high-resistance layer 110, and can achieve the same effects.

[0054] [Fourth Embodiment] This embodiment shows an example of a photoelectric conversion element provided with a light-shielding layer that absorbs light in the visible light range. The photoelectric conversion element 100 according to this embodiment has a structure that further includes a light-shielding layer 112 that absorbs light in the visible light range, compared to the configuration of the photoelectric conversion element shown in the first and second embodiments. In the following description, the differences from the first and second embodiments will be described in detail, and common parts will be omitted as appropriate.

[0055] Figure 5 shows a cross-sectional view of the photoelectric conversion element 100 according to this embodiment. Similar to the first embodiment, this photoelectric conversion element 100 has a structure in which an underlying insulating layer 103, an orientation control layer 104, and a photoelectric conversion structure 106 (first compound semiconductor layer 1062, second compound semiconductor layer 1064, and third compound semiconductor layer 1066) are laminated on an amorphous substrate 102. Figure 5 shows the case where the light-receiving surface of the photoelectric conversion element 100 is on the side of the third compound semiconductor layer 1066 of the photoelectric conversion structure 106. A light-shielding layer 112 is provided on the light-receiving surface side, superimposed on the photoelectric conversion structure 106.

[0056] The light-shielding layer 112 has the property of absorbing visible light and transmitting infrared light. The light-shielding layer 112 is formed of a III-V compound semiconductor material similar to the photoelectric conversion structure 106. The photoelectric conversion structure 106 is composed of a plurality of compound semiconductor layers. Among them, the second compound semiconductor layer 1064 responsible for the role of light absorption is compared. The light-shielding layer 112 preferably has a high transmittance for light in the wavelength band of infrared light absorbed by the second compound semiconductor layer 1064 while absorbing visible light. Comparing this relationship from the perspective of the bandgap, it is preferable that the bandgap Eg2 of the compound semiconductor forming the second compound semiconductor layer 1064 is smaller than the bandgap Eg1 of the compound semiconductor forming the light-shielding layer 112 (Eg1>Eg2).

[0057] Such control of the bandgap in the light-shielding layer 112 and the second compound semiconductor layer 1064 can be achieved by using different combinations of elements constituting the compound semiconductor materials forming the respective layers, or by varying the composition ratio while keeping the constituent elements the same.

[0058] For example, when the light-shielding layer 112 and the second compound semiconductor layer 1064 are formed of gallium arsenide antimonide (GaAsSb), the magnitude of the bandgap can be changed by varying the composition ratio of arsenic (As) and antimony (Sb). Specifically, for arsenic (As), the proportion contained in the light-shielding layer 112 is increased compared to the second compound semiconductor layer 1064, and for antimony (Sb), the proportion contained in the second compound semiconductor layer 1064 is increased compared to the light-shielding layer 112, so that the relationship Eg1>Eg2 of the bandgap can be realized. In other words, when the light-shielding layer 112 has a composition of Ga x1 As y1 Sb z1 (where x1 + y1+ z1 = 1) and the second compound semiconductor layer 1064 has a composition of Ga x2 As y2 Sb z2 (where x2 + y2+ z2 = 1), the relationship y1>y2, z1<z2 can realize the relationship Eg1>Eg2 of the bandgap.

[0059] When the second compound semiconductor layer 1064 is formed of indium nitride (InN) or indium gallium nitride (InGaN), the light-shielding layer 112 can be formed of aluminum indium nitride (AlInN) or indium gallium nitride (InGaN). In this example, the light-shielding layer 112 and the second compound semiconductor layer 1064 are formed of indium nitride-based III-V compound semiconductors, but by making the ratio of indium (In) in the light-shielding layer 112 smaller than that of the second compound semiconductor layer 1064, a relationship where the band gap Eg1 > Eg2 can be achieved.

[0060] Furthermore, it is preferable that the upper limit of the band gap in the light-shielding layer 112 be approximately 1.65 eV (750 nm). If the band gap Eg1 is greater than this value, it will transmit light in the visible light range, which is undesirable. In addition, it is preferable that the difference between the band gap Eg1 of the light-shielding layer 112 and the band gap Eg2 of the second compound semiconductor layer 1064 be 0.1 eV or more.

[0061] Preferably, the light-shielding layer 112 has crystalline properties similar to the second compound semiconductor layer 1064. The crystalline properties of the light-shielding layer 112 can reduce the defect density, reduce light absorption at the energy band edge (trim absorption), and improve the transmittance of light with wavelengths below the band gap Eg1.

[0062] In this way, by providing a light-shielding layer 112 on the light-receiving surface side of the photoelectric conversion structure 106, it is possible to prevent visible light from entering the photoelectric conversion structure 106 (or reduce the intensity of visible light). As a result, noise in the photoelectric conversion element 100 can be reduced and sensitivity can be improved.

[0063] Furthermore, the light-shielding layer 112 may have high resistance without dopants added. For this reason, it is preferable that the second electrode 108 penetrates the light-shielding layer 112 and contacts the third compound semiconductor layer 1066. On the other hand, the light-shielding layer 112 may be valence-controlled to have the same conductivity type as the third compound semiconductor layer 1066. In this case, the second electrode 108 can be provided in contact with the surface of the light-shielding layer 112.

[0064] Figure 6 shows a photoelectric conversion element 100 having a similar configuration to the photoelectric conversion element shown in the second embodiment, and further comprising a light-shielding layer 112 that absorbs visible light on the photoelectric conversion structure 106. As shown in Figure 6, by selectively providing the light-shielding layer 112 on the third compound semiconductor layer 1066, the intensity of visible light incident on the second compound semiconductor layer 1064 can be reduced, allowing infrared light to be incident.

[0065] Figure 7 shows a structure similar to the photoelectric conversion element shown in the second embodiment, in which a light-shielding layer 112 that absorbs visible light is continuously provided from the upper surface of the third compound semiconductor layer 1066 to the sides of the third compound semiconductor layer 1066 and the second compound semiconductor layer 1064, and to the upper surface of the first compound semiconductor layer 1062. In other words, the photoelectric conversion element 100 shown in Figure 7 has a structure in which the light-shielding layer 112 is provided so as to cover not only the upper surface of the photoelectric conversion structure 106, but also the upper and side surfaces exposed by etching. By having such a structure for the light-shielding layer 112, the influence of scattered light incident from the sides of the photoelectric conversion structure 106 can be reduced, and the sensitivity of the photoelectric conversion element 100 can be improved.

[0066] In this embodiment, the photoelectric conversion element 100 has a light-shielding layer 112 that absorbs visible light on the light-receiving surface, which prevents visible light from entering the photoelectric conversion structure 106 and improves the sensitivity when detecting infrared rays. Since the light-shielding layer 112 is made of a compound semiconductor, it can be formed continuously from the photoelectric conversion structure 106. That is, since the light-shielding layer 112 is made of a thin film of compound semiconductor, the productivity of the photoelectric conversion element 100 can be improved. Furthermore, since the light-shielding layer 112 is formed directly on the photoelectric conversion structure 106, the photoelectric conversion element 100 can be miniaturized.

[0067] The photoelectric conversion element 100 shown in the first to fourth embodiments can be applied to measuring blood glucose levels by being designed to be sensitive to infrared light in the wavelength band of 1.3 μm to 1.9 μm. Since the photoelectric conversion element 100 has a crystalline compound semiconductor deposited on an amorphous substrate 102 to form the photoelectric conversion structure 106, it can be made thinner and smaller. As a result, the photoelectric conversion element 100 can be mounted on portable electronic devices such as smartwatches without affecting their appearance, thereby improving the functionality and design of the electronic device.

[0068] Although this embodiment primarily describes a photoelectric conversion element that can be used as an infrared sensor, the photoelectric conversion element disclosed in this embodiment can also be used as a light sensor for light other than infrared light, as long as the light is within the wavelength range that can be photoconverted by the photoelectric conversion structure.

[0069] The various configurations of the photoelectric conversion element exemplified as one embodiment of the present invention can be combined as appropriate, as long as they do not contradict each other. Furthermore, any photoelectric conversion element disclosed in this specification and drawings, with additions, deletions, or design modifications of components, or additions, omissions, or changes in processes, made by those skilled in the art, are also included within the scope of the present invention, as long as they retain the essence of the present invention.

[0070] Any effects or benefits other than those brought about by the embodiments disclosed herein are to be understood to be brought about by the present invention if they are clear from the description herein or can be easily predicted by a person skilled in the art. [Explanation of symbols]

[0071] 100: Photoelectric conversion element, 102: Amorphous substrate, 103: Underlying insulating layer, 104: Orientation control layer, 106: Photoelectric conversion structure, 1062: First compound semiconductor layer, 1064: Second compound semiconductor layer, 1063: p-type compound semiconductor layer, 1065: p - Type compound semiconductor layer, 1066: third compound semiconductor layer, 107: first electrode, 108: second electrode, 110: high resistance layer, 112: light-shielding layer

Claims

1. Amorphous substrate and The orientation control layer on the amorphous substrate, The photoelectric conversion structure on the orientation control layer, It has, The photoelectric conversion structure is formed of a crystalline III-V compound semiconductor. A photoelectric conversion element characterized by the following features.

2. The band gap of the crystalline III-V compound semiconductor is 1.66 eV or less. The photoelectric conversion element according to claim 1.

3. The photoelectric conversion structure has a pn junction or a pin structure. The photoelectric conversion element according to claim 1.

4. The orientation control layer has c-axis oriented crystals and is conductive or insulating. The photoelectric conversion element according to claim 1.

5. The structure has a light-shielding layer that blocks at least visible light, and the light-shielding layer is positioned on the incident side of the photoelectric conversion structure. The photoelectric conversion element according to claim 1.

6. The light-shielding layer covers the upper and side surfaces of the photoelectric conversion structure. The photoelectric conversion element according to claim 5.

7. The light-shielding layer is formed of a III-V compound semiconductor. The photoelectric conversion element according to claim 5.

8. The photoelectric conversion structure is crystalline and is formed from one or more elements selected from InGaAs, InAsN, InAsP, InGaN, GaAsP, InAsN, GaAsSb, and InN. The photoelectric conversion element according to claim 1.

9. The light-shielding layer is crystalline and is formed of one or more materials selected from GaAsSb, InGaN, and AlInN. The photoelectric conversion element according to claim 7.

10. The amorphous substrate is a glass substrate or a resin substrate. The photoelectric conversion element according to claim 1.

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