JP2006032787A - Photoelectric conversion element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a field type photoelectric conversion element which can efficiently perform photoelectric conversion of incident light. <P>SOLUTION: In a photoelectric conversion device wherein one surface of a photoelectric conversion layer 102 is made a light receiving surface, a reflective layer 103 which reflects incident light is arranged on the opposite side of the light receiving surface of the photoelectric conversion layer 102. As a result, incident light which is made to enter the light receiving surface and reaches the bottom of the photoelectric conversion layer 102 and whose energy is not absorbed by the photoelectric conversion layer 102 is reflected by the reflective layer 103, and optical path length of the incident light can be lengthened. Hence, photoelectric conversion efficiency can be improved. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a photoelectric conversion element that is suitably used as a light receiving element in optical interconnection.

  As communication capacity increases, high-speed transmission by optical interconnection is expected. The basic configuration of the optical interconnection consists of a light emitting element such as a semiconductor laser (LD) or a light emitting diode, a light transmission unit such as an optical waveguide or an optical fiber, a photodiode or an avalanche diode (APD). : Avalanche Photo Diode).

  When the transmission speed of optical interconnection is on the order of Gbps, it becomes difficult to use a simple laser or photodiode as a light source or a light receiving source. A surface emitting laser (VCSEL), which is expected as a light emitting source, can form a large amount of lasers in a plane, and since it is a microcavity laser, direct modulation exceeding 10 Gbps is possible. As the light receiving element corresponding to the VCSEL, a direct transition type material such as gallium arsenide is used because the response speed of a photodiode made of silicon is not sufficient.

  However, a light receiving element using a direct transition type material such as gallium arsenide has a problem that the cost of the material itself is high, and the compatibility with silicon constituting an electronic circuit is inferior to that of a light receiving element made of silicon. .

  Therefore, in order to increase the light utilization efficiency of the light receiving element using silicon, Patent Document 1 discloses a photoelectric conversion device that efficiently converts incident light into an electric signal. FIG. 12 shows an embodiment disclosed in Patent Document 1. In patent document 1, it is comprised with the photoelectric conversion element of an end surface light reception type | mold, and the light leakage prevention member which covers the end surface except the light reception surface of the photoelectric conversion element, Since light is reflected by this light leakage prevention member, Use efficiency can be improved. Since this configuration uses an end face light receiving type photoelectric conversion element, it is considered that the same effect can be obtained even if an optical waveguide type photoelectric conversion element is used, for example, in order to increase the light utilization efficiency.

  As described above, in Patent Literature 1, light confinement in the in-plane direction of the photoelectric conversion element is realized by covering the end face except the light receiving surface of the photoelectric conversion element with a light leakage preventing member made of a photonic crystal. However, since there is no light confinement effect in the direction perpendicular to the plane, the light utilization efficiency is limited. When a VCSEL is used as the light source, optical signals are transmitted and received in the direction perpendicular to the plane, so that signals can be exchanged in the plane direction on the light receiving element side to facilitate mounting of the elements and connection to the transmission path. A surface type photoelectric conversion element capable of satisfying the demand is desired.

  By the way, regarding the planar photoelectric conversion element for high-speed transmission, in order to reduce the electron drift time, the absorption length width of the photoelectric conversion layer is reduced. For this reason, highly accurate alignment is required at the time of mounting, and if the alignment accuracy is low, the photoelectric conversion efficiency is reduced. Furthermore, since the transmission band changes with respect to the oblique component of the incident light, the light use efficiency is reduced for an incident light source that includes a large amount of the oblique component with a strongly focused beam. In order to detect a high-speed optical signal, it is necessary to suppress the time constant as an electric circuit. For this purpose, it is necessary to reduce the light receiving area. When processing an optical signal exceeding 40 Gbps in the future, for example, when the light receiving surface is circular, the diameter of the light receiving surface is 40 μm or less, and if the light is focused on the light receiving area, the angle component of the light beam is further increased. It is expected to increase, and it is necessary to deal with the oblique component of the incident light.

JP 2003-35845 A

  This invention is made | formed in view of the above, Comprising: It aims at providing the surface type photoelectric conversion element which can photoelectrically convert incident light efficiently.

  In order to solve the above-described problems and achieve the object, a photoelectric conversion element according to claim 1 is a photoelectric conversion element having a photoelectric conversion layer and having one surface of the photoelectric conversion layer as a light receiving surface. A first reflective layer that reflects incident light is provided on the opposite side of the light receiving surface of the photoelectric conversion layer.

  The invention according to claim 2 is the photoelectric conversion element according to claim 1, wherein the first reflective layer is made of a photonic crystal having a photonic band gap with respect to the wavelength of the incident light. Features.

  The invention according to claim 3 is the photoelectric conversion element according to claim 1 or 2, wherein the photonic crystal has a periodic refractive index distribution structure in a layer thickness direction of the first reflective layer. Features.

  According to a fourth aspect of the present invention, in the photoelectric conversion element according to any one of the first to third aspects, the photonic crystal has a periodic refractive index distribution structure in an in-plane direction of the first reflective layer. It is characterized by having.

  The invention according to claim 5 is the photoelectric conversion device according to any one of claims 1 to 4, wherein the photonic crystal has a periodic refractive index distribution structure in which dielectric columns are periodically arranged. It is characterized by having.

  The invention according to claim 6 is the photoelectric conversion element according to any one of claims 1 to 4, wherein the photonic crystal has a periodic refractive index distribution structure in which dielectric fine particle spheres are periodically arranged. It is characterized by having.

  The invention according to claim 7 is the photoelectric conversion element according to any one of claims 1 to 6, further transmitting at least part of incident light to the light receiving surface side of the photoelectric conversion layer, and A second reflective layer that reflects incident light reflected by the first reflective layer is provided.

  The invention according to claim 8 is the photoelectric conversion element according to claim 7, wherein the second reflective layer is made of a photonic crystal having a photonic band gap with respect to the wavelength of the incident light. Features.

  The invention according to claim 9 is the photoelectric conversion element according to claim 7 or 8, wherein the first reflection layer and the second reflection layer constitute a resonator. .

  The invention according to claim 10 is the photoelectric conversion element according to claim 1, wherein the first reflective layer includes at least a photonic crystal layer having a photonic band gap with respect to a wavelength of the incident light. It has a laminated structure in which two or more layers are laminated with a gap between each other, and adjacent photonic crystal layers included in the laminated structure each constitute a resonator. .

  According to an eleventh aspect of the present invention, in the photoelectric conversion element according to the tenth aspect, at least part of incident light is transmitted to the light receiving surface side of the photoelectric conversion layer, and the first reflective layer is provided. A second reflective layer that reflects the incident light reflected by the light source, and the second reflective layer includes at least two or more photonic crystal layers having a photonic band gap with respect to the wavelength of the incident light. The laminated structure has a laminated structure in which gaps are provided between each other, and adjacent photonic crystal layers included in the laminated structure each constitute a resonator.

  The invention according to claim 12 is the photoelectric conversion element according to any one of claims 1 to 11, wherein the photonic band gap is adjacent to the periphery of the end face of the photoelectric conversion layer with respect to the wavelength of the incident light. The photonic crystal has a periodic refractive index distribution structure in the in-plane direction of the photoelectric conversion layer.

  The invention according to claim 13 is the photoelectric conversion element according to any one of claims 1 to 12, wherein the first reflection layer changes a reflection direction of reflected light.

  The invention according to claim 14 is the photoelectric conversion element according to any one of claims 1 to 13, further comprising a deflection layer that changes a traveling direction of light on a light receiving surface side of the photoelectric conversion layer. And

  According to the first aspect of the invention, in the photoelectric conversion element having one surface of the photoelectric conversion layer as the light receiving surface, the first reflective layer that reflects incident light is provided on the opposite side of the light receiving surface. Of the incident light that has entered the photoelectric conversion layer, incident light that has reached the bottom of the photoelectric conversion layer without being absorbed by the photoelectric conversion layer is reflected by the first reflective layer to increase the optical path length of the incident light. Thus, the photoelectric conversion efficiency can be increased.

  According to the invention of claim 2, since the first reflective layer is formed of a photonic crystal having a photonic band gap with respect to the wavelength of the incident light, the photoelectric conversion layer does not absorb energy and photoelectrically Incident light that has reached the bottom of the conversion layer can be efficiently reflected, thereby increasing the photoelectric conversion efficiency.

  According to the invention of claim 3, since the photonic crystal having the periodic refractive index distribution structure in the layer thickness direction is used, the light incident from the vertical direction can be efficiently reflected, and thus the photoelectric conversion efficiency. There is an effect that can be increased.

  Further, according to the invention according to claim 4, since the photonic crystal having the periodic refractive index distribution structure in the in-plane direction is used, light incident from other than the vertical direction can be efficiently reflected, so that the photoelectric conversion is performed. There is an effect that the efficiency can be increased.

  Further, according to the invention of claim 5, since the reflective layer having a high reflection efficiency can be easily configured by the periodic refractive index distribution structure in which the dielectric pillars are periodically arranged, the photoelectric conversion is thus achieved. There is an effect that the efficiency can be increased.

  Further, according to the invention of claim 6, since the reflective layer having a high reflection efficiency can be easily configured by the periodic refractive index distribution structure formed by periodically arranging the dielectric fine particle spheres, There is an effect that the conversion efficiency can be increased.

  According to the invention of claim 7, by providing the second reflective layer on the light receiving surface side of the photoelectric conversion layer, the energy in the photoelectric conversion layer out of the reflected light reflected by the first reflective layer. Incident light that reaches the light-receiving surface of the photoelectric conversion layer without being absorbed can be reflected by the second reflective layer to further increase the optical path length of the incident light, thereby increasing the photoelectric conversion efficiency. There is an effect.

  According to the invention of claim 8, since the second reflective layer is formed of a photonic crystal having a photonic band gap with respect to the wavelength of the incident light, the photoelectric conversion layer does not absorb energy and photoelectrically The reflected light that has reached the light receiving surface of the conversion layer can be reflected efficiently, and the photoelectric conversion efficiency can be increased.

  According to the ninth aspect of the present invention, since the resonator is constituted by the first reflective layer and the second reflective layer, incident light can be confined in the photoelectric conversion layer for a long time, and thus the photoelectric There is an effect that the conversion efficiency can be increased.

  According to the invention of claim 10, the first reflective layer has at least two photonic crystal layers having a photonic band gap with respect to the wavelength of the incident light, and a gap is provided between them. By forming a multilayer structure by laminating and forming a multi-resonator, the resonance band can be widened, and the photoelectric conversion efficiency can be increased.

  According to the eleventh aspect of the present invention, by further providing the second reflective layer having the multiple resonator structure on the light receiving surface side, the resonance band can be widened, thereby improving the photoelectric conversion efficiency. There is an effect that can be done.

  According to the invention of claim 12, by disposing a photonic crystal having a periodic refractive index distribution structure in the in-plane direction of the photoelectric conversion layer adjacent to the periphery of the end face of the photoelectric conversion layer, Light that spreads in the plane of the photoelectric conversion layer and reaches the end face of the photoelectric conversion layer can be reflected by the photonic crystal adjacent to the periphery of the end face of the photoelectric conversion layer and returned to the photoelectric conversion layer, thereby providing photoelectric conversion efficiency. There is an effect that can be increased.

  According to the invention of claim 13, since the first reflection layer changes the reflection direction of the reflected light, the vertically incident light is confined in the photoelectric conversion layer, repeatedly reflected, and effective. As a result, the optical path length becomes longer, and the photoelectric conversion efficiency can be increased.

  According to the invention of claim 14, by providing the deflecting layer for changing the traveling direction of light on the light receiving surface side of the photoelectric conversion layer, vertically incident light is confined in the photoelectric conversion layer. Thus, the reflection is repeated, the effective optical path length is increased, and the photoelectric conversion efficiency can be increased.

  Exemplary embodiments of a photoelectric conversion element according to the present invention will be explained below in detail with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a cross-sectional view of the photoelectric conversion element according to the first embodiment of the present invention. The photoelectric conversion element according to the first embodiment includes a substrate 101, a photoelectric conversion layer 102, a reflective layer 103, a positive electrode 105, a negative electrode 106, a through hole 110, and an insulating layer 111.

  As shown in FIG. 1, a reflective layer 103 is laminated on the upper surface of the substrate 101, and a photoelectric conversion layer 102 is laminated on the upper surface of the reflective layer 103, and incident light is received from above the photoelectric conversion layer 102. The structure is incident. That is, the reflective layer 103 has a layer configuration provided on the opposite side of the light receiving surface of the photoelectric conversion layer 102. With such a layer structure, incident light that has entered the photoelectric conversion layer 102 and has reached the bottom of the photoelectric conversion layer 102 without being absorbed by the photoelectric conversion layer 102 is reflected by the reflective layer 103 and is subjected to photoelectric conversion. Returned in layer 102.

  The photoelectric conversion layer 102 is made of a material that can form an electron hole pair by receiving incident light. For example, the most common material is a semiconductor, and the photoelectric conversion layer 102 can be formed using silicon, gallium arsenide, indium phosphide, or a compound semiconductor based on them. The photoelectric conversion layer 102 has a p-side heavily doped layer 102a on the incident surface side and an n-side heavily doped layer 102b on the opposite side to the incident surface. The p-side heavily doped layer 102a is a donor for the semiconductor material constituting the photoelectric conversion layer 102, and the n-side heavily doped layer 102b is an acceptor for the semiconductor material constituting the photoelectric conversion layer 102. Formed by high concentration doping.

  The positive electrode 105 and the negative electrode 106 are electrically connected to the p-side heavily doped layer 102a and the n-side heavily doped layer 102b, respectively, and can extract current generated in the photoelectric conversion layer 102. The extracted current is sent to an external circuit as an electrical signal. In FIG. 1, the positive electrode 105 is formed on the p-side heavily doped layer 102 a via the insulating layer 111. Further, the negative electrode 106 is in electrical contact with the n-side highly doped layer 102 b through a through hole 110 formed in the photoelectric conversion layer 102. Since the purpose of the through hole 110 is to provide conduction on the negative electrode side, the through hole 110 may have a size that allows electrical contact with the n-side heavily doped layer 102b. That is, the size of the through hole 110 can be appropriately set according to the degree of freedom in device design.

  The reflective layer 103 is not particularly limited as long as it has a high reflectance in a wavelength range of incident light (for example, a wavelength range of 20 nm or more) and a low light absorptivity material, and may be a dielectric material or a metal. A desirable reflectance for the reflective layer 103 is 90% or more, preferably 95% or more, and more preferably 99% or more in the wavelength range of incident light. For example, if the wavelength of incident light is in the 850 nm band, copper, gold, and silver metal films have high reflectivity and low light absorptance, so that these metal films are used to transmit the photoelectric conversion layer 102. The light can be fed back to the photoelectric conversion layer 102 again, and the light use efficiency can be increased.

  Incident light that enters from the p-side light-receiving surface is absorbed by the photoelectric conversion layer 102 to form electron hole pairs. In the electron hole pair, due to an electric field generated by applying a reverse bias, electrons move to the positive electrode 105 and holes move to the negative electrode 106 to generate a current.

  The photoelectric conversion amount of the photoelectric conversion element is proportional to the length of incident light passing through the inside of the photoelectric conversion layer 102, that is, the optical path length. Therefore, by increasing the optical path length, the light use efficiency of incident light is improved. be able to. In general, in the surface-receiving photoelectric conversion element, the photoelectric conversion layer 102 is designed to be thick in order to increase the optical path length. However, when the photoelectric conversion layer 102 is thickened, there is a problem that an electrical restriction such as a need to increase the reverse bias voltage appears. Therefore, an optical waveguide type device has been proposed as a method for improving the light utilization efficiency by increasing the optical path length while keeping the reverse bias voltage low. However, alignment adjustment is performed to make light incident on the optical waveguide. Therefore, alignment adjustment for making light incident on an extremely thin light absorption layer is very difficult.

  According to the first embodiment, the reflective layer 103 is provided on the opposite side of the incident surface of the photoelectric conversion layer 102, and the light that enters the photoelectric conversion layer 102 from the p-side light receiving surface is reflected by the reflective layer 103. As a result, the optical path length can be increased. For this reason, it is possible to improve the light utilization efficiency with a simple configuration without increasing the thickness of the photoelectric conversion layer 102 or adjusting the alignment with high accuracy like an optical waveguide photoelectric conversion element.

(Second Embodiment)
FIG. 2 is a cross-sectional view of the photoelectric conversion element according to the second embodiment of the present invention. In the second embodiment, the same reference numerals are given to the same components as those in the first embodiment, and the description thereof is omitted.

  The second embodiment is characterized in that a photonic crystal having a photonic band gap (light propagation prohibition band) with respect to the wavelength of incident light is used as the reflective layer 201. A photonic crystal is a crystal that has a periodic distribution of refractive index inside by combining materials with different refractive indices with a period of the order of the wavelength of light. It has a band gap. The second embodiment uses the property of a photonic crystal that cannot propagate light of a specific wavelength, and uses this as a reflection layer.

  In the second embodiment, a periodic refractive index distribution structure (hereinafter, referred to as the wavelength of incident light) in the layer thickness direction is formed by laminating a large number of pairs of low refractive index medium layers and high refractive index medium layers. A one-dimensional photonic crystal made of a multilayer film to which a periodic structure may be abbreviated) is used. A high reflectance can be obtained as a distributed Bragg reflector by designing the film thickness of each film constituting the multilayer film with an optical thickness of ¼ wavelength of incident light. In the second embodiment, it is preferable to stack at least 5 pairs of a low refractive index medium layer and a high refractive index medium layer, and the reflectance can be increased by increasing the number of stacked layers. Such a multilayer film can be prepared using a known method such as sputtering.

  In photonic crystals, the greater the difference in refractive index between the low-refractive index medium layer and the high-refractive index medium layer, the more the reflectivity can be improved, so the combination of the low-refractive index medium and the high-refractive index medium is selected. In this case, it is preferable to select a combination in which the difference in refractive index between the two is preferably 1% or more, more preferably 3% or more. The material of the multilayer film is not particularly limited as long as the material can sufficiently ensure the difference in refractive index between the low refractive index medium layer and the high refractive index medium layer. For example, a known material can be used. Examples thereof include a film, a dielectric multilayer film, or a composite multilayer film in which a semiconductor layer and a dielectric layer are combined.

  Examples of the semiconductor multilayer film that can be used as the photonic crystal include materials such as gallium arsenide / aluminum gallium arsenide and indium phosphide / gallium indium arsenide phosphorus. When a photonic crystal is formed by a semiconductor multilayer film, a low refractive index medium layer and a high refractive index medium layer may be sequentially stacked by a known crystal growth technique. A material that can be grown by the crystal growth technique needs to be formed of a material in which the lattice spacing of material atoms is matched. For this reason, in the semiconductor multilayer film, the material properties of the low refractive index medium layer and the high refractive index medium layer are close to each other, and it may be difficult to obtain a sufficient refractive index difference. In general, when the reflective layer 201 is formed of a semiconductor multilayer film, several tens of pairs of a low refractive index medium layer and a high refractive index medium layer are stacked in order to achieve sufficient reflectance. preferable.

  Examples of the dielectric multilayer film include materials and materials such as silicon dioxide / magnesium oxide and silicon dioxide / zirconia dioxide. In the case of a dielectric multilayer film, a combination having a large difference in refractive index can be selected as the low refractive index medium layer and the high refractive index medium layer, so that a reflectivity of 99% or more is obtained with the number of stacked layers of about 10 pairs. be able to.

  As described above, according to the second embodiment, since the reflective layer 201 is formed of a one-dimensional photonic crystal having a photonic band gap with respect to the wavelength of incident light, energy is generated in the photoelectric conversion layer 102. Incident light that reaches the bottom of the photoelectric conversion layer without being absorbed can be efficiently reflected, and the photoelectric conversion efficiency can be increased.

(Third embodiment)
FIG. 3 is a cross-sectional view of a photoelectric conversion element according to the third embodiment of the present invention. Note that, in the third embodiment, components that are the same as those in the first embodiment are assigned the same reference numerals, and descriptions thereof are omitted.

  The third embodiment is characterized in that a three-dimensional photonic crystal having a periodic structure of about the wavelength of incident light in the layer thickness direction and in-plane direction is used as the reflective layer 301. A three-dimensional photonic crystal has a periodic structure in the layer thickness direction and in-plane direction by processing individual thin films of a low refractive index medium and a high refractive index medium by lithography and dry etching, and laminating them alternately. It can be formed by applying.

  The reflective layer 301 made of a three-dimensional photonic crystal does not need to be provided on the entire surface between the substrate and the photoelectric conversion layer, and has a slightly larger area than the light receiving surface, for example, about 1.5 times the area of the light receiving surface. It is enough.

  As described above, according to the third embodiment, by using a three-dimensional photonic crystal for the reflective layer 301, it is possible to realize a high reflectance in a wide band that cannot be obtained with a one-dimensional photonic crystal. In addition, it is possible to prevent a decrease in reflectance due to the incident angle.

(Fourth embodiment)
FIG. 4 is a cross-sectional view of a photoelectric conversion element according to the fourth embodiment of the present invention. Note that in the fourth embodiment, identical symbols are assigned to components common to the first embodiment and descriptions thereof are omitted.

  The fourth embodiment is characterized in that a three-dimensional photonic crystal constituting the reflective layer 401 is formed by regularly stacking dielectric columns 401a.

  The three-dimensional photonic crystal of the fourth embodiment has an asymmetric face centered cubic structure. The asymmetric face-centered cubic structure is a complete three-dimensional structure that gives a photonic band gap in all directions. In this way, by forming a reflective layer using a three-dimensional photonic crystal having a structure in which a photonic band gap opens in all directions of the wave number space, an incident light source having an incident angle other than normal incidence can be obtained. High reflectivity can be realized.

  The shape of the dielectric pillar 401a used for forming the asymmetric face-centered cubic structure may be a square pillar or a cylinder. It is preferable that the dielectric has a high dielectric constant. If the dielectric constant difference between the dielectric pillar and the medium surrounding it is large, the photonic band gap is widened, and a high reflectance is obtained in a wide band. For example, if a photonic crystal is formed with silicon pillars in the air, the difference in refractive index can be increased, and a high reflectance can be obtained in a wide band of about 50 nm.

  The material of the dielectric pillar 401a is preferably a material that is transparent at the wavelength of light to be received. For example, when the wavelength is 1.3 μm, glass, semiconductor materials such as silicon, gallium arsenide, and indium phosphide can be raised.

  The asymmetric face-centered cubic structure can be formed by alternately stacking dielectric columns 403a. First, the dielectric pillars 401a are arranged in parallel at a constant pitch on the substrate 101 to form a first layer. Next, the second layer is formed on the first layer by rotating the dielectric columns 401a in parallel at the same pitch by rotating 90 degrees. Next, a third layer is formed on the second layer by arranging the dielectric pillars 401a in parallel with a half-pitch shift from the arrangement of the first layer. Further, the fourth layer is formed on the third layer by arranging the dielectric pillars 401a in parallel with the arrangement of the second layer shifted by a half pitch. By repeating these lamination steps, a three-dimensional photonic crystal having an asymmetric face-centered cubic structure can be formed.

  For example, when the dielectric pillar 401a made of a semiconductor is used, an asymmetric face-centered cubic structure can be formed by a semiconductor fusion technique. The semiconductor fusion technology is to perform surface treatment on the same or different semiconductors, introduce hydroxyl groups on the surface, bond the semiconductor surfaces by hydrogen bonding of hydroxyl groups, and remove water molecules by heating at high temperature in a hydrogen atmosphere. In this process, molecular bonds on the substrate surface are obtained. It can be formed by forming submicron semiconductor pillar structures on the substrate 101 by lithography and etching, aligning and fusing them with high accuracy, and repeating the operation of removing the substrate 101. Further, for example, if the dielectric pillar 401a is made of silicon, the photoelectric conversion layer 102 and the reflective layer 401 made of a three-dimensional photonic crystal can be made of the same material. 401 and the photoelectric conversion layer 102 can be manufactured.

  In the asymmetric face-centered cubic structure, an ultraviolet curable resin layer is formed on the substrate 101, and a part of the ultraviolet curable resin is cured by irradiating the ultraviolet curable resin with a short pulse laser to form a column shape. You may produce by the method. By using this method, it is possible to manufacture a periodic structure by simply changing the laser focusing position. Alternatively, a groove larger than the light receiving radius may be formed in the substrate 101 by lithography and etching, an ultraviolet curable resin may be embedded in the groove, and a photonic crystal structure may be formed by laser irradiation.

  After forming the reflective layer 401 made of a three-dimensional photonic crystal, the photoelectric conversion layer 102 is bonded onto the reflective layer 401 to form an electrode. Note that when the electrode is formed and when the through hole 110 is opened in the vicinity of the light receiving surface, it is necessary to align the reflective layer 401 and the light receiving surface. However, the photoelectric conversion layer 102 is extremely about 10 microns. Since it is thin, alignment can be facilitated by patterning the alignment mark on the reflective layer 401 before the step of bonding the photoelectric conversion layer 102 on the reflective layer 401.

  The reflective layer 401 made of a three-dimensional photonic crystal having an asymmetric face-centered cubic structure does not need to be provided on the entire surface between the substrate and the photoelectric conversion layer, and has an area slightly larger than the light receiving surface, for example, 1.5 of the light receiving surface. A double area is sufficient.

  According to the fourth embodiment, a high reflectivity in a wide band can be realized by using a photonic crystal having a complete three-dimensional structure that provides a photonic band gap in any direction for the reflective layer 401. At the same time, it is possible to prevent a decrease in reflectance due to the incident angle.

(Fifth embodiment)
FIG. 5 is a cross-sectional view of a photoelectric conversion element according to a fifth embodiment of the present invention. Note that in the fifth embodiment, identical symbols are assigned to components common to the first embodiment and descriptions thereof are omitted.

  The fifth embodiment is characterized in that the three-dimensional photonic crystal constituting the reflective layer 501 is formed by regularly stacking submicron-sized dielectric spheres 501a. In the fifth embodiment, a three-dimensional photonic crystal having a diamond structure is formed by periodically arranging dielectric spheres 501a.

  The periodic arrangement of the dielectric spheres 501a can be formed by stacking fine particle spheres having a uniform particle diameter. The diameter of the dielectric sphere 501a is, for example, about 50 nm to 500 nm. Examples of the material for the fine particle sphere include polystyrene, silicon dioxide, and titanium dioxide.

  In the three-dimensional photonic crystal having a diamond structure, a groove having an area larger than the light receiving diameter is formed on the substrate 101 by lithography and etching, and dielectric spheres 501a having a uniform particle diameter are dispersed in the groove in the liquid. The dielectric sphere dispersion solution is dropped and the liquid in which the dielectric spheres are dispersed is evaporated.

  The constituent material of the dielectric sphere 501a is preferably a material that is transparent to the wavelength of incident light, and more preferably a material having a large refractive index. After the reflective layer 501 made of a three-dimensional photonic crystal having a diamond structure is formed, the photoelectric conversion layer 102 is bonded to the reflective layer 501, and an electrode is formed on the photoelectric conversion layer 102.

  As described above, according to the fifth embodiment, the reflection layer 501 uses a photonic crystal having a complete three-dimensional structure that gives a photonic band gap in all directions, thereby providing high reflectivity in a wide band. Can be realized, and a decrease in reflectance due to the incident angle can be prevented.

(Sixth embodiment)
FIG. 6 is a cross-sectional view of a photoelectric conversion element according to a sixth embodiment of the present invention. Note that in the sixth embodiment, identical symbols are assigned to components common to the first embodiment and descriptions thereof are omitted.

  The sixth embodiment is an application example of the fifth embodiment, and the reflective layer 501 is configured by periodically arranging the air spheres 601a in the high refractive index filler 601b. Features. That is, in the fifth embodiment, the dielectric sphere 501a is arranged in the air and has a structure in which the refractive index of the sphere portion is larger than that of the air, but the sixth embodiment has this refractive index. It is an example of the structure where distribution was reversed. That is, the photonic crystal is formed by setting the dielectric constant of the air sphere 601a to be lower than the refractive index of the surrounding filler 601b. As a manufacturing method, after manufacturing the structure using the dielectric sphere shown in FIG. 5, a material having a high refractive index is embedded between the dielectric spheres, and the array of the dielectric spheres is removed by etching to form air spheres. Etc.

  As described above, according to the sixth embodiment, the reflective layer 601 has a periodic structure in which the air spheres 601a are periodically arranged, and the air is a medium having a dielectric constant higher than that of the air spheres 601a. A photonic crystal can also be formed by filling the periphery of the sphere 601a, and the light utilization efficiency can be improved.

(Seventh embodiment)
FIG. 7 is a cross-sectional view of a photoelectric conversion element according to a seventh embodiment of the present invention. Note that in the seventh embodiment, identical symbols are assigned to components common to the first embodiment and descriptions thereof are omitted.

  In the seventh embodiment, a first reflection layer 701 that reflects incident light is provided on the opposite side of the light receiving surface of the photoelectric conversion layer 102, and further, incident light is incident on the light receiving surface side of the photoelectric conversion layer 102. A second reflective layer 703 that transmits at least part of the light and reflects incident light reflected by the first reflective layer 701 is provided.

  In FIG. 7, the first reflective layer 701 and the second reflective layer 703 are configured by photonic crystals using dielectric microspheres 501a of submicron size, as in the fifth embodiment.

  In the seventh embodiment, the first reflective layer 701 is made thicker so that a high light reflectance can be realized as a reflective film, and the second reflective layer 703 is more than the first reflective layer 701. The amount of light coupled to the photoelectric conversion layer 102 is increased by increasing the light transmittance by reducing the layer thickness.

  Incident light that has entered from the p-side light-receiving surface passes through the second reflective layer 703 and is absorbed by the photoelectric conversion layer 102 to generate a current. Of the incident light, incident light that reaches the bottom of the photoelectric conversion layer 102 without being absorbed by the photoelectric conversion layer 102 is reflected by the first reflection layer 701 and returned to the photoelectric conversion layer 102 to generate a current. . Of the reflected light reflected by the first reflective layer 701, incident light that reaches the surface of the photoelectric conversion layer 102 without being absorbed by the photoelectric conversion layer 102 is reflected by the second reflective layer 703 and again becomes photoelectrical. Returned to the conversion layer 102 to generate current. Thus, by repeating light reflection between the first reflective layer 701 and the second reflective layer 703, the optical path length can be further increased, and the light utilization efficiency can be improved. Become.

  In the seventh embodiment, the first reflective layer 701 and the second reflective layer 703 are configured using the submicron-sized dielectric spheres 501a. However, as long as incident light can be reflected, The configuration of the reflective layer is not particularly limited. The first reflective layer 701 and the second reflective layer 703 do not necessarily have the same configuration. For example, the first reflective layer 701 is a metal layer, and the second reflective layer 703 is made of a photonic crystal. It is also possible to configure.

  As described above, according to the seventh embodiment, by providing reflection layers on both sides of the photoelectric conversion layer 102, light reflection is repeated between the two reflection layers, and the optical path length is further increased. Therefore, the light use efficiency can be improved.

(Eighth embodiment)
FIG. 8 is a sectional view of a photoelectric conversion element according to an eighth embodiment of the present invention. Note that in the eighth embodiment, identical symbols are assigned to components common to the first embodiment and descriptions thereof are omitted.

  In the eighth embodiment, the first reflective layer 801 and the second reflective layer 803 are provided on the opposite side and the light receiving surface side of the photoelectric conversion layer 102, respectively. The first reflective layer 801 and the second reflective layer 803 constitute a resonator by adjusting the three-dimensional periodic structure of the photonic crystal of the 801 and the second reflective layer 803. .

  By adjusting the three-dimensional periodic structure of the first reflective layer 801 and the second reflective layer 803, the resonance state of the resonator can be controlled, and the light transmittance and Q value in the wavelength band of interest can be controlled. It becomes possible to control. The Q value is a value representing the properties of the resonator. When the Q value is large, light can be confined in the resonator for a long time, and the effective resonator length can be increased. Therefore, it is possible to improve the light utilization efficiency.

  As described above, according to the eighth embodiment, the first reflective layer 801 and the second reflective layer 803 constitute a resonator to confine incident light in the photoelectric conversion layer 102 for a long time. Thus, the photoelectric conversion efficiency can be increased.

(Ninth embodiment)
FIG. 9 is a cross-sectional view of a photoelectric conversion element according to the ninth embodiment of the present invention. Note that in the ninth embodiment, identical symbols are assigned to components common to the first embodiment and descriptions thereof are omitted.

  As shown in FIG. 9, a first reflective layer 901 and a second reflective layer 903 are provided on the opposite side and the light receiving surface side of the photoelectric conversion layer 102, respectively.

  In the ninth embodiment, the first reflective layer 901 has a laminated structure in which at least two photonic crystal layers 901a are laminated. The second reflective layer 903 also has a stacked structure in which at least two or more photonic crystal layers 903a are stacked. The spacer layers 901b and 903b are interposed between the photonic crystal layers 901a and 903a so that a gap is provided between the photonic crystal layers 901a and 903a.

  The ninth embodiment is characterized in that a resonator is configured between adjacent photonic crystal layers by adjusting a periodic structure such as a film thickness of each of the photonic crystal layers 901a and 903a. By forming a resonator between the adjacent photonic crystal layers 901a and between the adjacent photonic crystal layers 903a, between the first reflective layer 901, the photoelectric conversion layer 102, and the second reflective layer 903 Multiple resonators can be formed, and the resonance band can be further expanded. If the resonance band can be widened, it is possible to cover the oscillation wavelength fluctuation of the VCSEL, and the light utilization efficiency can be improved.

  The first reflective layer 901 and the second reflective layer 903 as described above form a periodic structure of the photonic crystal layers 901a and 903a, and spacer layers 901b and 903b made of the same material as the photoelectric conversion layer 102 thereon. And a periodic structure of photonic crystal layers 901a and 903a can be formed on the spacer layers 901b and 903b. By repeating this manufacturing process, a multiple resonator can be formed.

  The resonator formed between the adjacent photonic crystal layers 901a and 903a adjusts the size of the dielectric fine particle spheres that form the periodic structure of the photonic crystal layers 901a and 903a, thereby allowing light in the wavelength band of interest. It is possible to control the transmittance and the Q value.

  As described above, according to the ninth embodiment, by forming a multiple resonator among the first reflective layer 901, the photoelectric conversion layer 102, and the second reflective layer 903, the resonance band can be further increased. Since it can be further expanded, the photoelectric conversion efficiency can be increased.

(Tenth embodiment)
FIG. 10 is a cross-sectional view of a photoelectric conversion element according to the tenth embodiment of the present invention. Note that in the tenth embodiment, identical symbols are assigned to components common to the first embodiment and descriptions thereof are omitted.

  In the tenth embodiment, the first reflective layer 1001 and the second reflective layer 1003 are provided on the opposite side and the light receiving surface side of the photoelectric conversion layer 102, respectively, and around the end surface of the photoelectric conversion layer 102. A photonic crystal 1004 having a periodic refractive index distribution structure is disposed adjacent to the photoelectric conversion layer 102 in the in-plane direction.

  By providing a photonic crystal 1004 having a periodic refractive index distribution structure in the in-plane direction around the end face of the photoelectric conversion layer 102, light that has spread in the plane of the photoelectric conversion layer 102 and has reached the end face of the photoelectric conversion layer 102 can be obtained. It can be reflected by the photonic crystal 1004 around the end face and returned into the photoelectric conversion layer 102.

  The photonic crystal 1004 around the end face of the photoelectric conversion layer 102 is provided to reflect light that has spread in the plane of the photoelectric conversion layer back to the photoelectric conversion layer 102 and improve light utilization efficiency. The photonic crystal 1004 is formed around the light receiving region of the photoelectric conversion layer 102 and need not be formed in the light receiving region.

  Such a photonic crystal 1004 has a periodic structure in the in-plane direction of the photoelectric conversion layer 102 by lithography and etching around the light receiving region of the photoelectric conversion layer 102 after the photoelectric conversion layer 102 is formed on the entire surface of the substrate 101. Can be created by forming.

  As described above, according to the tenth embodiment, by providing the photonic crystal 1004 having a periodic refractive index distribution structure in the in-plane direction of the photoelectric conversion layer 102 around the end face of the photoelectric conversion layer 102. The light that spreads in the plane of the photoelectric conversion layer 102 and reaches the end face of the photoelectric conversion layer 102 can be reflected by the photonic crystal 1004 around the end face and returned into the photoelectric conversion layer 102, so that the photoelectric conversion efficiency Can be increased.

(Eleventh embodiment)
FIG. 11 is a sectional view of a photoelectric conversion element according to an eleventh embodiment of the present invention. Note that in the eleventh embodiment, identical symbols are assigned to components common to the first embodiment and descriptions thereof are omitted.

  The eleventh embodiment is characterized in that a reflective layer 1101 having an inclination with respect to the incident surface is provided between the photoelectric conversion layer 102 and the substrate 101. By making the reflective layer 1101 an inclined surface, the reflection direction of the light reflected by the reflective layer 1101 can be changed as shown in FIG. The reflective layer 1101 may be a metal layer or a photonic crystal layer, as long as it has a high reflectance with respect to the wavelength of the input light source.

  By adjusting the refractive index between the photoelectric conversion layer 102 and the reflective layer 1101 and the inclination of the reflective layer 1101, light perpendicularly incident from the p-side light receiving surface is confined in the photoelectric conversion layer 102. , Repeat reflection. For this reason, the effective optical path length becomes long and the light utilization efficiency is improved.

  As described above, according to the eleventh embodiment, the reflection direction of the reflected light can be changed by providing the reflection layer 1101 having an inclination with respect to the incident surface, and the effective optical path length. Therefore, the light utilization efficiency can be improved.

  Although not shown, a layer that changes the traveling direction of incident light is also provided on the photoelectric conversion layer 102, so that vertically incident light is confined in the photoelectric conversion layer and reflected. Repeatedly, the effective optical path length becomes longer and the light utilization efficiency is improved. Examples of the layer that changes the traveling direction of incident light include a deflecting layer having a deflecting action, a layer non-parallel to the incident surface, and a layer having a diffraction grating structure.

  As described above, since the photoelectric conversion element of the present invention is a planar photoelectric conversion element that can efficiently convert incident light, it can be suitably used as a light receiving element when a VCSEL is used as a light emission source. Can do.

It is sectional drawing of the photoelectric conversion element concerning 1st Embodiment. It is sectional drawing of the photoelectric conversion element concerning 2nd Embodiment. It is sectional drawing of the photoelectric conversion element concerning 3rd Embodiment. It is sectional drawing of the photoelectric conversion element concerning 4th Embodiment. It is sectional drawing of the photoelectric conversion element concerning 5th Embodiment. It is sectional drawing of the photoelectric conversion element concerning 6th Embodiment. It is sectional drawing of the photoelectric conversion element concerning 7th Embodiment. It is sectional drawing of the photoelectric conversion element concerning 8th Embodiment. It is sectional drawing of the photoelectric conversion element concerning 9th Embodiment. It is sectional drawing of the photoelectric conversion element concerning 10th Embodiment. It is sectional drawing of the photoelectric conversion element concerning 11th Embodiment. It is sectional drawing of the photoelectric conversion element of a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Substrate 102 Photoelectric conversion layer 102a P-side highly doped layer 102b n-side highly doped layer 103 Reflective layer 105 Positive electrode 106 Negative electrode 110 Through hole 111 Insulating film 201 Reflective layer 301 Reflective layer 401 Reflective layer 401a Columnar body 501 Reflective layer 501a Fine particles Sphere 601 Reflective layer 601a Air sphere 601b Filler 701 First reflective layer 703 Second reflective layer 801 First reflective layer 803 Second reflective layer 901 First reflective layer 901a Photonic crystal layer 901b Spacer layer
903 Second reflective layer 903a Photonic crystal layer 903b Spacer layer 1001 First reflective layer 1003 Second reflective layer 1004 Photonic crystal 1101 Reflective layer

Claims (14)

A photoelectric conversion element having a photoelectric conversion layer and having one surface of the photoelectric conversion layer as a light receiving surface,
A photoelectric conversion element comprising a first reflection layer that reflects incident light on a side opposite to a light receiving surface of the photoelectric conversion layer.   The photoelectric conversion element according to claim 1, wherein the first reflective layer is made of a photonic crystal having a photonic band gap with respect to a wavelength of the incident light.   The photoelectric conversion element according to claim 1, wherein the photonic crystal has a periodic refractive index distribution structure in a layer thickness direction of the first reflective layer.   The photoelectric conversion element according to claim 1, wherein the photonic crystal has a periodic refractive index distribution structure in an in-plane direction of the first reflective layer.   The photoelectric conversion element according to any one of claims 1 to 4, wherein the photonic crystal has a periodic refractive index distribution structure in which dielectric columns are periodically arranged.   The photoelectric conversion element according to any one of claims 1 to 4, wherein the photonic crystal has a periodic refractive index distribution structure in which dielectric fine particle spheres are periodically arranged.   Furthermore, a second reflective layer that transmits at least part of incident light and reflects incident light reflected by the first reflective layer is provided on the light receiving surface side of the photoelectric conversion layer. The photoelectric conversion element according to any one of claims 1 to 6.   The photoelectric conversion element according to claim 7, wherein the second reflective layer is made of a photonic crystal having a photonic band gap with respect to a wavelength of the incident light.   The photoelectric conversion element according to claim 7, wherein the first reflective layer and the second reflective layer constitute a resonator. The first reflective layer includes
The photonic crystal layer having a photonic band gap with respect to the wavelength of the incident light has a laminated structure in which at least two layers are laminated with a gap therebetween,
2. The photoelectric conversion element according to claim 1, wherein adjacent photonic crystal layers included in the stacked structure each constitute a resonator. Furthermore, the light receiving surface side of the photoelectric conversion layer has a second reflection layer that transmits at least part of incident light and reflects incident light reflected by the first reflection layer,
The second reflective layer is
The photonic crystal layer having a photonic band gap with respect to the wavelength of the incident light has a laminated structure in which at least two layers are laminated with a gap therebetween,
The photoelectric conversion element according to claim 10, wherein adjacent photonic crystal layers included in the laminated structure constitute a resonator. A photonic crystal having a photonic band gap with respect to the wavelength of the incident light adjacent to the periphery of the end face of the photoelectric conversion layer;
The said photonic crystal has a periodic refractive index distribution structure toward the in-plane direction of the said photoelectric converting layer, The photoelectric conversion element as described in any one of Claims 1-11 characterized by the above-mentioned.   The photoelectric conversion element according to claim 1, wherein the first reflective layer changes a reflection direction of reflected light.   The photoelectric conversion element according to claim 1, further comprising a deflection layer that changes a traveling direction of light on a light receiving surface side of the photoelectric conversion layer.

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