JP5437486B2 - Photoelectric conversion element - Google Patents

Description

  The present invention relates to a photoelectric conversion element applied to, for example, a photodiode or a solar cell, and more particularly to a photoelectric conversion element that synergistically uses a Schottky effect and a surface plasmon effect.

For example, Patent Document 1 describes a photoelectric conversion element using surface plasmon resonance. An uneven structure having a uniform period is formed on the surface of the metal layer of the element. A semiconductor layer is laminated on the concavo-convex structure, and a transparent electrode is further laminated thereon. Another electrode is laminated on the back surface of the metal layer. When light is incident on the element, electrons on the surface of the metal layer on the concave-convex structure side vibrate in resonance with the incident light, and a current is generated.
In the photoelectric conversion element described in Patent Document 2, two or more kinds of fine particles are provided on the surface, and surface plasmon resonance is caused in at least two wavelength bands.

Further, it has been known since the 1960s that visible light can be detected by a Schottky optical sensor in which Au having a thickness of several μm or more is stacked on n-type Si.
Non-Patent Document 1 describes that near-infrared light of 1 μm to ₂ μm can be detected by an optical sensor in which CoSi ₂ is laminated on n-type Si.
Non-Patent Document 2 describes that infrared light of 1 μm to 5 μm can be detected by an optical sensor in which CoSi ₂ is laminated on p-type SiGe.
Non-Patent Document 3 describes that infrared light of 1 μm to 6 μm can be detected by an optical sensor in which Pt is stacked on p-type Si.
Non-Patent Document 4 describes that light of 10 μm or less can be detected by an optical sensor in which Ir is laminated on Si.

JP 2007-073794 A JP 2010-021189 A

Roca, Elisenda, et al., Proceedings of SPIE-The International Society for Optical Engineering 2525 (2), 456 (1995) S. Kolondinski, et al., Proceedings of SPIE-The International Society for Optical Engineering 2554, 175 (1995) J.M.Mooney and J.Silverman, IEEE Trans.Electron DevicesED-32, 33-39 (1985) B-Y.Tsaur, M.M.Weeks, R.Trubiano and P.W.Pellegrini, IEEE Electron Device Left.9,650-653 (1988)

  However, a photoelectric conversion element that is sensitive to a wide band from visible light to infrared light is not known. In any of the known photoelectric conversion elements, it is not easy to reduce the thickness because carriers flow in the stacking direction (thickness direction) of the elements.

  Therefore, it is conceivable to stack a conductive layer on the semiconductor layer, dispose a pair of electrodes on this conductive layer, and dispose a plasmon resonance structure on the surface of the conductive layer between the electrodes. However, it is uncertain which of the pair of electrodes becomes the anode and which becomes the cathode, and the direction of the current cannot be determined. Each electrode can be an anode or a cathode due to contamination or disturbance incidentally or inevitably mixed in the manufacturing process, and there is no guarantee that the current-voltage characteristics are asymmetric between the positive side and the negative side.

In order to solve the above problems, the photoelectric conversion element according to the present invention is:
an n-type or p-type semiconductor layer;
A conductive layer laminated on the semiconductor layer;
A first electrode provided on the conductive layer or the semiconductor layer;
A polarity determining layer interposed between the first electrode and the conductive layer;
A second electrode provided on the conductive layer;
A metal nanostructure including a plurality (preferably a large number) of periodic structures stacked on the conductive layer;
Wherein the comprises a first protrusion plurality of projecting direction of each periodic structure the stacked, arrangement intervals of the first convex portion and wherein not claimed to vary depending on the periodic structure.
The photoelectric conversion element according to the present invention is characterized in that an n-type or p-type semiconductor layer, a conductive layer stacked on the semiconductor layer, a first electrode provided on the conductive layer, and a photocarrier A barrier layer interposed between the first electrode and the conductive layer with a thickness that can pass through the tunnel effect; and a second electrode provided on the conductive layer apart from the first electrode; A metal nanostructure including a plurality of periodic structures stacked on the conductive layer, wherein each periodic structure is composed of a plurality of first protrusions protruding in the direction of the stack, and the arrangement of the first protrusions The interval is different depending on the periodic structure. The barrier layer constitutes the polarity determining layer.

When light enters the photoelectric conversion element, photocarriers are generated by photoelectric conversion at the Schottky junction between the semiconductor layer and the conductive layer. In addition, the sensitivity of photoelectric conversion can be increased by the metal nanostructure in the vicinity of the Schottky junction. Furthermore, the wavelength region of incident light that can be photoelectrically converted by the metal nanostructure can be widened.
When the semiconductor layer is an n-type semiconductor, photocarrier electrons move to the semiconductor layer side by the electric field of the depletion layer. Along with this, electrons flow from the second electrode into the conductive layer. Electrons (current) can flow smoothly between the second electrode and the conductive layer. Electrons flow along the conductive layer toward the first electrode. Therefore, the first electrode becomes a cathode. The second electrode becomes an anode.
When the semiconductor layer is a p-type semiconductor, photocarrier holes move to the semiconductor layer side by the electric field of the depletion layer. Along with this, holes flow from the second electrode into the conductive layer. Holes flow toward the first electrode along the conductive layer. Therefore, the first electrode becomes an anode. The second electrode becomes a cathode.
Therefore, the electrode to be the anode and the electrode to be the cathode can be determined, and the direction of the photoinduced current can be controlled. Therefore, the current-voltage characteristic is reliably asymmetric between the positive side and the negative side, and a clean diode characteristic can be obtained.

The barrier layer is preferably composed of an insulator having a thickness of less than 1 nm. Thus, the conductive layer and the first electrode constitute a capacitor with the barrier layer interposed therebetween. Accordingly, carriers are accumulated in a portion of the conductive layer facing the first electrode. When the semiconductor layer is an n-type semiconductor, electrons are accumulated. When the semiconductor layer is a p-type semiconductor, holes are accumulated. As a result, the electrode to be the anode and the electrode to be the cathode can be reliably determined. By setting the thickness of the insulator to less than 1 nm, carriers can surely pass through the barrier layer by the tunnel effect or the like, and the photo-induced current can be reliably taken out. Furthermore, carriers are accumulated in a portion of the conductive layer facing the first electrode, whereby the voltage resistance is improved, and the current-voltage characteristics during light irradiation are shifted to the forward bias side (positive side). Therefore, the generated power of the photoelectric conversion element can be increased.

The polarity determining layer is a convex layer integrally protruding from the semiconductor layer, and the convex layer is in Schottky contact with the end surface of the conductive layer on the first electrode side and in ohmic contact with the first electrode. Tei also good. As a result, carriers can flow toward the convex layer side and thus toward the first electrode at the Schottky junction between the convex layer and the conductive layer. Therefore, the electrode to be the anode and the electrode to be the cathode can be reliably determined.

  Since the pair of electrodes are disposed on the same surface of the photoelectric conversion element, the photoelectric conversion element can be thinned.

  Examples of the metal component constituting the conductive layer include Co, Fe, W, Ni, Al, and Ti. These metal elements listed have relatively high melting points and excellent mechanical properties at high temperatures. The conductive layer may be a metal, or a mixture or alloy of a metal and a semiconductor. Examples of the metal or semiconductor mixture or alloy include metal silicide. When the semiconductor layer is made of silicon, the conductive layer may be a metal silicide formed by diffusing the metal component and the surface layer portion of the semiconductor layer. The diffusion can be performed by, for example, annealing. The metals listed above (Co, Fe, W, Ni, Al, Ti) are suitable for silicidation.

Plasmon resonance occurs when light enters the metal nanostructure. Thereby, the metal nanostructure contributes to the increase of the light-induced electric field.
The metal nanostructure is preferably an aggregate of nanosized metal fine particles.
As the metal constituting the metal nanostructure, Au, Ag, Pt, Cu, or Pd is preferably used. These listed metal elements have relatively high chemical stability, are not easily alloyed, and are not easily combined with a semiconductor such as Si. Therefore, surface plasmon can be formed reliably.

  The metal nanostructure is preferably provided in a portion between the pair of electrodes in the conductive layer, and more preferably widely distributed in a portion between the pair of electrodes.

  The metal nanostructure is formed as follows, for example. A metal raw material to be the metal nanostructure is disposed on the conductive layer and annealed. The annealing temperature condition is, for example, about 400 ° C. to 800 ° C., and preferably about 600 ° C. The shape or property of the metal raw material is not particularly limited, and may be any of a thin film shape, a small piece shape, a small lump shape, a granular shape, a powder shape, a colloidal shape, a fiber shape, a wire shape, and a dot shape. It may be a property. By the annealing treatment, the fine particles of the metal raw material diffuse along the surface of the conductive layer. Due to the diffusion, the fine particles of the metal raw material are branched in multiple stages or multiple, for example, an aggregate having a fractal structure. Thereby, the metal nanostructure can be easily formed. Sub-micron or nano-order irregularities are formed on the surface of the metal nanostructure. The surface of the metal nanostructure includes a large number of protrusions protruding in the stacking direction (thickness direction), for example, in a cluster shape.

  The electrode may also be used as a metal raw material for the metal nanostructure. The metal constituting the electrode may be diffused around the electrode in a cluster shape or a fractal shape by annealing. Then, the metal nanostructure can be formed in the vicinity of the electrode. In this case, the electrode and the metal nanostructure include the same metal component.

  In the metal nanostructure, it is preferable that the periodic structure has a random period. It is preferable that the period of the periodic structure is changed. That is, it is preferable that the arrangement interval of the first protrusions differs according to the periodic structure. Thereby, it can respond to the light of a different wavelength according to a periodic structure. Therefore, the wavelength range in which the metal nanostructure can be sensitive as a whole can be widened. Therefore, it is possible to provide a photoelectric conversion element that can cope with a wide band extending from the visible light region to the infrared light region.

The arrangement interval (period) of the first protrusions is preferably about 0.1 to 1 times the wavelength λ of the incident light, and more preferably about 0.1 times the wavelength λ. Alternatively, the arrangement interval (period) of the first protrusions is preferably about 0.1 to 1 times the sensitive wavelength of the Schottky element formed by the semiconductor layer and the conductive layer. The periodic structure is sensitively sensitive to incident light having a wavelength λ of about 1 to 10 times (particularly about 10 times the period) of the period of the first convex portion constituting the periodic structure, and plasmon resonance. This contributes to the amplification of the light-induced electric field. It is preferable that the period of the periodic structure of the n-type element in the semiconductor layer (arrangement interval of the first protrusions) is smaller than the period of the periodic structure of the p-type element in the semiconductor layer (arrangement interval of the first protrusions). In an element having an n-type semiconductor layer, the arrangement interval (period) of the first protrusions is more preferably about 100 nm or less. Thereby, it can have a favorable sensitivity with respect to the light of the infrared light range-visible light range whose wavelength is about 1 micrometer or less. In an element having a p-type semiconductor layer, the arrangement interval (period) of the first protrusions is more preferably about 150 nm or less. Thereby, it can have a favorable sensitivity with respect to the infrared light whose wavelength is about 1 micrometer-4 micrometers.
The protruding height of the first convex portion is preferably about 10 nm to 20 nm.

  At least one of the periodic structures is about 0.1 to 1 times as large as any wavelength within a certain wavelength range (preferably from the visible light region to the infrared light region) (particularly about 0.1 times the size). ) Is preferably provided. Thus, if the incident light is included in the wavelength range, at least one periodic structure of the metal nanostructure can be sensitive to the incident light.

The metal nanostructure further includes a plurality of second protrusions protruding in the stacking direction from the first protrusions, the second protrusions are dispersed from each other, and each second protrusion is formed of the periodic structure. It is preferable that they are arranged so as to overlap or be close to any one.
When light enters the metal nanostructure, near-field light is generated around the second convex portion. Due to the synergistic effect of this near-field light and plasmon resonance due to the periodic structure, a photo-induced electric field can be amplified with high sensitivity and output (K. Kobayashi, et.al., Progress in Nano-Electro-Optecs I. ed. M See Ohtsu, p.119 (Sptinger-Verlag, Berlin, 2003). Even if the incident light is weak, the photovoltaic force can be generated with high sensitivity.

The protrusion height of the second protrusion is preferably about 50 nm to 200 nm.
The dispersion interval of the second protrusions (the distance between adjacent second protrusions) is preferably greater than the wavelength of incident light, and is greater than the sensitive wavelength of a Schottky element formed by the semiconductor layer and the conductive layer. preferable.
It is preferable that the dispersion interval of the 2nd convex part of the element whose semiconductor layer is n type is smaller than the dispersion interval of the 2nd convex part of the element whose semiconductor layer is p type. For example, when the semiconductor layer is n-type, the dispersion interval of the second protrusions is preferably 1 μm or more, and more preferably about 2 μm to 3 μm. When the semiconductor layer is p-type, it is preferable that the dispersion interval of the second protrusions is about 3 μm to 5 μm. Thereby, it can avoid that the adjacent 2nd convex part interferes and weakens an electric field.
The upper limit of the dispersion interval of the second protrusions is preferably about 3 μm to 5 μm for the n-type, and preferably about 5 μm to 6 μm for the p-type. As a result, the existence density of the second protrusions can be ensured, the number of periodic structures that can cause interaction with the second protrusions can be ensured, and the sensitive band can be reliably widened.

  An insulator such as a carbon compound may be mixed in the metal nanostructure to form an MIM structure.

  A nanostructure made of a semiconductor having sensitivity in the ultraviolet region or infrared region may be further provided on the surface of the photoelectric conversion element. In particular, when the semiconductor layer is an n-type semiconductor, it is preferable to provide a nanostructure made of a semiconductor having sensitivity in the ultraviolet region on the surface of the photoelectric conversion element. A semiconductor having sensitivity in the ultraviolet region refers to a semiconductor having a property that carriers are excited when irradiated with ultraviolet light having a wavelength of 0.4 μm or less. As such a semiconductor, for example, zinc oxide (ZnO) which is an n-type semiconductor can be given, and in addition, n-type gallium nitride (n-GaN) and the like can be mentioned. When the semiconductor layer is a p-type semiconductor, it is preferable to provide a nanostructure made of a semiconductor having sensitivity in the infrared region on the surface of the photoelectric conversion element. A semiconductor having sensitivity in the infrared region refers to a semiconductor having a property in which carriers are excited when irradiated with infrared light having a wavelength of, for example, 0.7 μm or more. Examples of such a semiconductor include p-type gallium nitride (p-GaN) and carbon. Examples of nanostructures include nanowires, nanotubes, nanoneedles, and nanorods. The nanostructure can increase the sensitivity of photoelectric conversion. When the nanostructure is made of a semiconductor having sensitivity in the ultraviolet region, the photoelectric conversion sensitivity to incident light in the ultraviolet region can be increased. When the nanostructure is made of a semiconductor having sensitivity in the infrared region, the photoelectric conversion sensitivity to incident light in the infrared region can be increased. By configuring the nanostructure with nanowires, nanotubes, or the like, the quantum efficiency can be increased, and the sensitivity of the photoelectric conversion element can be reliably increased.

  According to the present invention, the electrode to be the anode and the electrode to be the cathode of the photoelectric conversion element can be reliably determined, and asymmetric diode characteristics can be obtained.

FIG. 1 is a cross-sectional view showing a schematic structure of a photoelectric conversion element according to the first embodiment of the present invention. FIG. 2 is an equivalent circuit diagram of the photoelectric conversion element. FIG. 3 is a graph showing a model of current-voltage characteristics of the photoelectric conversion element. FIG. 4 is a cross-sectional view showing a schematic structure of a photoelectric conversion element according to the second embodiment of the present invention. FIG. 5 is a cross-sectional view showing a schematic structure of a photoelectric conversion element according to the third embodiment of the present invention. FIG. 6 is a cross-sectional view showing a schematic structure of a photoelectric conversion element according to the fourth embodiment of the present invention. FIG. 7 is a cross-sectional view showing a schematic structure of a photoelectric conversion element according to the fifth embodiment of the present invention. FIG. 8A is an image obtained by observing one part of the surface of the metal nanostructure in Example 1 with an SEM (scanning electron microscope). FIG. 8B is an image obtained by observing a portion of the surface of the metal nanostructure in Example 1 different from that in FIG. FIG. 9 is a stereoscopic image obtained by observing the surface structure of the metal nanostructure in Example 1 with an AFM (atomic force microscope). FIG. 10 is an explanatory diagram of the stereoscopic image of FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a photoelectric conversion element 1 according to the first embodiment of the present invention. The photoelectric conversion element 1 includes a semiconductor layer 11, a conductive layer 20, a metal nanostructure 30, and a pair of electrodes 41 and 42. A conductive layer 20 is stacked on the semiconductor layer 11. Metal nanostructures 30 are stacked on the conductive layer 20. In addition, a pair of electrodes 41 and 42 are provided on the conductive layer 20. A polarity determining layer 50 is interposed between the first electrode 41 and the conductive layer 20. FIG. 2 is an equivalent circuit diagram of the photoelectric conversion element 1. The photoelectric conversion element 1 has a structure including a diode and a capacitor.
Hereinafter, the structure of the photoelectric conversion element 1 will be described in detail.

  As shown in FIG. 1, the semiconductor layer 11 is made of silicon (Si). However, the present invention is not limited to this, and the semiconductor layer 11 may be composed of another semiconductor such as Ge or GaAs. The semiconductor layer 11 is doped with an n-type impurity such as P (phosphorus). The semiconductor layer 11 constitutes an n-type semiconductor.

  As shown in FIG. 1, the semiconductor layer 11 also serves as a substrate for the photoelectric conversion element 1. The semiconductor layer 11 is composed of a silicon substrate. The silicon substrate is doped with n-type impurities. A silicon wafer or the like can be used as the silicon substrate. The silicon substrate ensures the shape retention and mechanical rigidity of the photoelectric conversion element 1. The substrate may be provided separately from the semiconductor layer 11. For example, the n-type semiconductor layer 11 may be coated on a substrate made of glass or a resin film. The n-type semiconductor layer 11 may be formed on the surface of the separate substrate by CVD or the like.

The conductive layer 20 covers the entire surface of the semiconductor layer 11 (upper surface in FIG. 1). The conductive layer 20 is made of metal silicide and has conductivity. Silicon on the surface layer of the semiconductor layer 11 is self-organized to constitute a silicon component of the conductive layer 20. Examples of the metal component constituting the conductive layer 20 include Co, Fe, W, Ni, Al, and Ti. However, the metal component is not limited to these. Here, Co is used as a metal component constituting the conductive layer 20. Conductive layer 20 is formed by CoSix, preferably are composed of CoSi _2. Thereby, a good Schottky interface is formed between the conductive layer 20 and the semiconductor layer 11. The conductive layer 20 may be composed of only a metal component. The thickness of the conductive layer 20 is about several nm to several tens of nm, preferably about several nm.
The thickness of the conductive layer 20 in the drawing is exaggerated with respect to the thickness of the semiconductor layer 11, the electrodes 41 and 42, the metal nanostructure 30, and the like.

  Metal nanostructures 30 are provided on the surface of the conductive layer 20 (upper surface in FIG. 1). The metal nanostructures 30 are widely distributed on the surface of the conductive layer 20. Here, the metal nanostructure 30 is disposed in a portion between the pair of electrodes 41 and 42 on the surface of the conductive layer 20 (hereinafter referred to as “interelectrode portion”), and more preferably the interelectrode portion. Distributed throughout. The metal nanostructure 30 may be stacked only on a part of the conductive layer 20. For example, the metal nanostructure 30 may be provided only in the vicinity of the electrode 41 or 42 of the conductive layer 20.

  The metal nanostructure 30 is composed mainly of a metal such as Au, Ag, Pt, Cu, or Pd. Here, Au is used as the metal constituting the metal nanostructure 30. The metal nanostructure 30 is an Au-rich structure. An insulator such as a carbon compound may be mixed in the metal constituting the metal nanostructure 30, and the metal nanostructure 30 has a metal-insulator-metal (MIM) metal-insulator-metal (MIM) structure. It may be.

  The surface of the metal nanostructure 30 has submicron or nano-order irregularities. More specifically, the metal nanostructure 30 has a structure in which Au nanoparticles are aggregated in a cluster shape or a fractal shape (see FIGS. 9 and 10). The aggregate of Au nano-particles of the metal nanostructure 30 includes a large number of protrusions protruding in the thickness direction or stacking direction (upward) of the element 1. These convex portions are gathered in a cluster. Alternatively, it has a fractal structure in which an aggregate of Au nanoparticles is diffused so as to branch multiple times. The metal nanostructure 30 includes a large number of first protrusions 31 and second protrusions 32. A part of the many convex parts constitutes the first convex part 31, and the other part constitutes the second convex part 32.

  The metal nanostructure 30 has at least one periodic structure 30. Preferably, the metal nanostructure 30 has a plurality, a large number, or an infinite number of periodic structures 33. One periodic structure 33 is constituted by the plurality of adjacent convex portions 31, 31... In the above-described many convex portions of the metal nanostructure 30. The first protrusions 31, 31... Constituting each periodic structure 33 are arranged at a certain interval (period) along the surface direction of the element 1 (direction orthogonal to the stacking direction). The arrangement interval (period) of the first convex portions 31 differs depending on the periodic structure 33. The arrangement interval (period) of the first protrusions 31 in these periodic structures 33 is preferably about several tens of nm to several μm, and more preferably about 40 nm to 100 nm. This arrangement interval (period) is preferably about 0.1 to 1 times the wavelength of the incident light L, and more preferably about 0.1 times. Further, the arrangement interval (period) is about 0.1 to 1 times the sensitive wavelength (visible light region to infrared light region) of the Schottky element composed of the n-type semiconductor layer 10 and the conductive layer 40. It is preferable. The metal nanostructure 30 preferably includes at least one periodic structure having an arrangement interval that is approximately 0.1 to 1 times the arbitrary wavelength within the sensitive region of the Schottky element.

  Furthermore, a plurality of second convex portions 32 are arranged in the metal nanostructure 30 in a dispersed manner. Each 2nd convex part 32 is arrange | positioned so that one of the periodic structures 33 may overlap. Or each 2nd convex part 32 is arrange | positioned in the vicinity of one of the periodic structures 33. FIG. The second convex portion 32 has a protruding height larger than that of the first convex portion 31 and has a sharpness (ratio of the protruding height and the width of the bottom portion) larger than that of the first convex portion 31. The protruding height of the second convex portion 32 is preferably about 50 nm to 200 nm. The dispersion interval between the second convex portions 32 is preferably larger than the wavelength of the incident light. For example, the dispersion interval is preferably 1 μm or more, and preferably about 2 μm to 3 μm. The upper limit of the dispersion interval between the second convex portions 32 is preferably about 3 μm to 5 μm.

  The pair of electrodes 41 and 42 are disposed on the conductive layer 20 at positions separated from each other. Here, the first electrode 41 is disposed at one end (on the right in FIG. 1) of the upper surface of the conductive layer 20. The second electrode 42 is disposed on the other end portion (left side in FIG. 1) of the upper surface of the conductive layer 20. The arrangement of the electrodes 41 and 42 is not limited to the above. For example, one of the electrodes 41 and 42 may be disposed at the central portion of the element 1, and the other of the electrodes 41 and 42 may be disposed at the four corners (peripheral portions) of the element 1.

The electrodes 41 and 42 are made of a metal such as Au, Ag, Pt, Cu, or Pd. Here, Au is used as the metal constituting the electrodes 41 and 42. Therefore, the electrodes 41 and 42 are composed of the same metal component as that constituting the metal nanostructure 30.
The metal component constituting the metal nanostructure 30 and the metal component constituting the electrodes 41 and 42 may be different from each other. The two electrodes 41 and 42 may be composed of different metal components.

Between the 1st electrode 41 and the conductive layer 20, the barrier layer 50 is provided as a polarity determination layer. The barrier layer 50 is made of an insulator such as alumina, SiO ₂ , SiN, or a carbon compound (for example, resin). The thickness of the barrier layer 50 is small enough to cause a tunnel effect. For example, the thickness of the barrier layer 50 is angstrom order, ie less than 1 nm. In the drawing, the thickness of the barrier layer 50 is exaggerated with respect to the thickness of the conductive layer 20, the metal nanostructure 30, and the like. The first electrode 41 and the conductive layer 20 are opposed to each other with the barrier layer 50 interposed therebetween, thereby forming a capacitor.

  The second electrode 42 and the conductive layer 20 are in direct contact. Preferably, the second electrode 42 is in ohmic contact with the conductive layer 20.

A method for manufacturing the photoelectric conversion element 1 will be described.
[Conductive layer material coating process]
A P-doped n-type silicon substrate 11 is prepared. Co, which is a raw material component of the conductive layer 20, is formed on the substrate 11. As the Co film forming method, PVD (Physical Vapor Deposition) such as sputtering or vapor deposition can be employed. Not limited to PVD, Co may be coated by other film forming methods such as spin coating.

[Barrier placement process]
A barrier layer 50 made of an insulating material (for example, alumina) having an angstrom order thickness is disposed at a position where the first electrode 41 is to be disposed on the Co film. The arrangement of the barrier layer 50 can be performed by various film forming methods such as CVD.

[Electrode placement process]
A metal raw material (Au) to be the first electrode 41 is provided on the barrier layer 50. Further, a metal raw material (Au) to be the second electrode 42 is provided at a position where the second electrode 42 is to be disposed on the Co film. The metal raw material (Au) for the electrodes 41 and 42 can be arranged by various film forming methods such as sputtering and vapor deposition.

[Metal nanostructure raw material placement process]
Further, a metal raw material (Au) that becomes the metal nanostructure 30 is disposed between the electrodes 41 and 42 on the Co film. The shape or property of the metal raw material (Au) of the metal nanostructure 30 is not particularly limited, and is a thin film shape, small piece shape, small lump shape, granular shape, powder shape, colloidal shape, fiber shape, wire shape, dot shape, and the like. Any of these may be used, and other shapes or properties may be used. When the metal raw material (Au) is in the form of a thin film, it can be formed by PVD such as sputtering or vapor deposition. A part of the metal raw material (Au) to be the electrodes 41 and 42 can be diffused into the inter-electrode part in the diffusion step described later to form the metal nanostructure 30, in which case the metal nanostructure raw material arranging step is omitted. May be.

[Diffusion process]
Next, the substrate 11 is placed in an annealing treatment tank and an annealing treatment is performed. The temperature condition for the annealing treatment is preferably about 400 ° C. to 800 ° C., more preferably about 600 ° C. The annealing treatment is performed in a 100% inert gas atmosphere as much as possible. As the inert gas for the annealing treatment, a rare gas such as He, Ar, Ne or the like can be used, and N ₂ may also be used. The pressure condition for the annealing treatment is in the vicinity of atmospheric pressure, for example, about several Pa lower than atmospheric pressure.

  By the annealing process, Co diffuses into Si constituting the surface portion of the substrate 11. As a result, the CoSix conductive layer 20 formed by self-organizing the surface portion of the Si substrate 11 is formed, and the semiconductor layer 11 and the conductive layer 20 can be securely bonded by Schottky.

Further, by the annealing treatment, Au fine particles arranged on the conductive layer 20 are diffused so as to form clusters or fractals along the surface of the conductive layer 20. That is, Au fine particles diffuse so as to branch into multiple, and become an aggregate of a fractal structure. The surface of the aggregate has sub-micron or nano-order irregularities and is clustered. Thereby, the metal nanostructure 30 can be formed naturally.
The diffusion step may be performed by a method other than annealing.

The operation of the photoelectric conversion element 1 will be described.
At one end of the photoelectric conversion element 1 (right in FIG. 1), the conductive layer 20 and the first electrode 41 constitute a capacitor with the barrier layer 50 interposed therebetween. A current can flow smoothly between the second electrode 42 at the other end (left in FIG. 1) and the conductive layer 20.
When light having a wavelength in the visible region to the infrared region (specifically, a wavelength of about 0.4 μm to 2 μm) is incident on the photoelectric conversion element 1, a Schottky junction with the CoSix layer 20 in the n-Si layer 11. Thus, photocarriers are generated by photoelectric conversion. Furthermore, the sensitivity of photoelectric conversion can be increased by the metal nanostructure 30 in the vicinity of the Schottky junction. Moreover, the wavelength range of light that can be photoelectrically converted can be expanded by the metal nanostructure 30.

  The photocarrier electrons generated at the Schottky junction move to the n-Si layer 11 side by the electric field of the depletion layer. Along with this, electrons flow from the second electrode 42 into the conductive layer 20. Electrons flow toward the first electrode 41 along the conductive layer 20. Electrons are accumulated in a portion of the conductive layer 20 facing the first electrode 41. The electrons can pass through the barrier layer 50 by the tunnel effect and move to the first electrode 41. Thereby, a photo-induced current can be taken out. Accordingly, the first electrode 41 becomes a cathode. The second electrode 42 becomes the anode. In this way, the electrode 42 serving as the anode and the electrode 41 serving as the cathode can be determined, and the direction of the photoinduced current can be controlled. Therefore, as shown in FIG. 3, the current-voltage characteristic can be reliably asymmetrical between the positive side and the negative side, and a clean diode characteristic can be obtained.

  Furthermore, since electrons are accumulated in the portion of the conductive layer 20 facing the first electrode 41, the withstand voltage is improved, and the voltage-current characteristics during light irradiation are forward biased (as shown by the solid line in FIG. Shift to the positive side. Thereby, the output power corresponding to the area of the shaded portion in FIG. 3 can be increased.

  Since the photo-induced electric field is formed along the surface of the element 1, carriers are accelerated along the surface of the element 1 and can move at a high speed of the compound semiconductor level. Therefore, it is possible to realize an ultra-high-speed imaging sensor or a photodetection sensor that can cope with light modulation waves in the GHz to THz band. Since the photoelectric conversion element 1 is a thin film type, it can also be used as a CCD sensor array.

  The operation of the metal nanostructure 30 will be described in detail. Plasmons are localized on the surface of the Au nanoparticle constituting the metal nanostructure 30. The surface plasmon and incident light resonate to generate a large electric field. The periodic structure 33 of the metal nanostructure 30 enhances the sensitivity of photoelectric conversion with respect to incident light having a wavelength corresponding to the period (the arrangement interval of the first protrusions 31). That is, the periodic structure 33 is sensitively sensitive to incident light having a wavelength of about 1 to 10 times, particularly about 10 times the period, and causes plasmon resonance. Since the period of the 1st convex part 31 changes according to the periodic structure 33, the wavelength range which the metal nanostructure 30 can respond can be widened. Further, near-field light is generated around the second convex portion 32. A large light-induced electric field can be generated by a synergistic effect of the near-field light and the plasmon resonance by the periodic structure 33. As a result, it is possible to provide the photoelectric conversion element 1 that is sensitive to a wide band extending from the visible light region to the infrared light region. Even if the incident light is weak, the photovoltaic force can be generated with high sensitivity. By making the dispersion interval of the second convex portions 32 larger than the wavelength of incident light (visible light region to infrared light region), preferably 1 μm or more, more preferably 2 μm to 3 μm, adjacent second convex portions 32. , 32 can interfere with each other and weaken the electric field. By setting the upper limit of the dispersion interval of the second convex portions 32 to 3 μm to 5 μm, the existence density of the second convex portions 32 can be maintained high, and the number of the periodic structures 33 that can cause the interaction with the second convex portions 32 is increased. Can be secured, and the sensitive band can be reliably widened. Therefore, it is possible to provide the photoelectric conversion element 1 that can cope with a wide band extending from the visible light region to the infrared light region.

Therefore, when the photoelectric conversion element 1 is used as a light detection sensor, it has excellent sensitivity characteristics and can detect broadband light.
When the photoelectric conversion element 1 is used as a solar cell, sunlight in a wide band can be photoelectrically converted and used for electric power. Sufficiently large electric power can be obtained not only in fine weather but also in cloudy weather. Furthermore, even after sunset, power can be obtained by photoelectrically converting infrared light scattered in the atmosphere. By absorbing infrared light, thermal conversion of infrared light can be prevented, and it can also be expected as a measure against global warming.
Since the pair of electrodes 41 and 42 are disposed on the same surface (upper surface) of the element 1, the photoelectric conversion element 1 can be thinned.

Next, another embodiment of the present invention will be described. In the following embodiments, the same reference numerals are attached to the drawings for the same contents as those already described, and the description thereof is omitted.
FIG. 4 shows a second embodiment of the present invention. A photoelectric conversion element 1A according to the second embodiment includes a p-type semiconductor layer 12 instead of the n-type semiconductor layer 11 of the first embodiment. The p-type semiconductor layer 12 is made of p-type silicon doped with a p-type impurity such as B (boron). The p-type semiconductor layer 12 is also the same as the first embodiment in that it also serves as a substrate.

  The arrangement interval (period) of the first protrusions 31 in the periodic structure 33 of the p-type element 1A is preferably slightly larger than that of the n-type element 1, for example, about 60 nm to 150 nm is more preferable. The dispersion interval of the second convex portions 32 in the periodic structure 33 of the p-type element 1A is preferably slightly larger than that of the n-type element 1. For example, the dispersion interval is preferably about 3 μm to 5 μm, and the upper limit is preferably about 5 μm to 6 μm.

  The p-type photoelectric conversion element 1 </ b> A is more sensitive than the n-type photoelectric conversion element 1 in an infrared light region having a longer wavelength (specifically, a wavelength of about 1 μm to 4 μm). When light in this sensitivity band enters the photoelectric conversion element 1A, photocarriers are generated by photoelectric conversion at the Schottky junction of the p-Si layer 12 with the CoSix layer 20. Of these photocarriers, holes move to the p-Si layer 12 side by the electric field of the depletion layer. As a result, holes flow from the second electrode 42 into the conductive layer 20. Holes flow toward the first electrode 41 along the conductive layer 20. Holes are accumulated in the portion of the conductive layer 20 facing the first electrode 41. The holes can pass through the barrier layer 50 by the tunnel effect and move to the first electrode 41. Thereby, a photo-induced current can be taken out. Accordingly, the first electrode 41 becomes an anode. The second electrode becomes the cathode. In this way, the electrode 41 serving as the anode and the electrode 42 serving as the cathode can be determined, and the direction of the photoinduced current can be controlled. Therefore, the current-voltage characteristic can be reliably asymmetrical between the positive side and the negative side, and a clean diode characteristic can be obtained.

  FIG. 5 shows a third embodiment of the present invention. The third embodiment relates to a modification of the photoelectric conversion element 1 (first embodiment) having the n-type semiconductor layer 11. An n-type semiconductor nanostructure 61 is provided on the surface (upper surface in FIG. 5) of the photoelectric conversion element 1 having the n-type semiconductor layer 11. The n-type semiconductor nanostructure 61 is composed of zinc oxide nanowires. Zinc oxide is an n-type semiconductor. The nanostructure 61 is provided so as to protrude from the surface of the photoelectric conversion element 1. Here, the nanostructure 61 protrudes from the metal nanostructure 30. In addition, when the metal nanostructure 30 is coated only on a part of the conductive layer 20, the nanostructure 61 may protrude from the conductive layer 20 in a portion where the metal nanostructure 30 is not coated. . The nanowire can be formed by CVD, PVD, sol-gel method or the like. The nanostructure 61 is not limited to a nanowire, and may be a nanoneedle, a nanotube, or a nanorod.

  The zinc oxide nanostructure 61 can increase the photoelectric conversion sensitivity to incident light having a relatively short wavelength (ultraviolet light to visible light). Specifically, the sensitivity can be improved for light from an ultraviolet light region of less than about 0.4 μm to a visible light region of about 1 μm. By configuring the nanostructure 61 with nanowires, the quantum efficiency can be increased, and as a result, the sensitivity of the photoelectric conversion element 1 can be reliably increased.

  FIG. 6 shows a fourth embodiment of the present invention. The fourth embodiment relates to a modification of the photoelectric conversion element 1A (second embodiment) having the p-type semiconductor layer 12. A p-type semiconductor nanostructure 62 is provided on the surface (upper surface in FIG. 6) of the photoelectric conversion element 1 </ b> A having the p-type semiconductor layer 12. The p-type semiconductor nanostructure 62 is composed of carbon nanotubes, and is provided so as to protrude from the surface of the photoelectric conversion element 1A. Here, the p-type semiconductor nanostructure 62 protrudes from the metal nanostructure 30. In addition, when the metal nanostructure 30 is coated only on a part of the conductive layer 20, the nanostructure 62 may protrude from the conductive layer 20 in a portion where the metal nanostructure 30 is not coated. . The carbon nanotube can be formed by CVD, PVD, sol-gel method or the like. The nanostructure 62 is not limited to a nanotube, and may be a nanowire, a nanoneedle, or a nanorod.

  The carbon nanostructure 62 can increase the photoelectric conversion sensitivity to infrared light. Specifically, the sensitivity can be improved for infrared light of about 2 μm to about 4 μm. By configuring the nanostructure 62 with carbon nanotubes, the quantum efficiency can be increased, and as a result, the sensitivity of the photoelectric conversion element 1A can be reliably increased.

FIG. 7 shows a fifth embodiment (not claimed) of the present invention. The fifth embodiment relates to a modification of the polarity determining layer. The n-type photoelectric conversion element 1 is provided with a convex layer 51 as a polarity determining layer instead of the barrier layer 50 described above. The convex layer 51 is formed integrally with the n-type semiconductor layer 11. A portion near the first electrode 41 on the surface (upper surface) of the semiconductor layer 11 protrudes, and this protruding portion constitutes the convex layer 51. The convex layer 51 is interposed between the first electrode 41 and the end of the conductive layer 20 on the first electrode 41 side. The protruding height of the convex layer 51 is approximately the same as the thickness of the conductive layer 20, for example, approximately 1 nm to 10 nm, and preferably approximately several nm. The width dimension (left and right dimensions in FIG. 7) of the convex layer 51 is, for example, 0. It is several mm to several mm, preferably about 1 mm. In FIG. 7, the protrusion height (vertical dimension) of the convex layer 51 is exaggerated with respect to the width (horizontal dimension).

  One side surface (left side surface in FIG. 7) of the convex layer 51 is in Schottky contact with the end surface of the conductive layer 20. The other side surface (right side surface in FIG. 7) of the convex layer 51 is in ohmic contact with the first electrode 41. The metal nanostructure 30 is formed so as to straddle the upper surface of the convex layer 51 from the conductive layer 20. The metal nanostructure 30 may be provided only on the upper surface of the convex layer 51. Alternatively, the metal nanostructure 30 may be provided only on the upper surface of the conductive layer 20.

  When light is incident on the n-type photoelectric conversion element 1 according to the fifth embodiment, photocarriers are generated at the Schottky junction between the bottom of the conductive layer 20 and the semiconductor layer 11. Photo carriers are also generated at the Schottky contact portion between the right end portion and the convex layer 51. The electrons of the carriers flow to the convex layer 51 side and thus to the first electrode 41 by a depletion layer electric field between the conductive layer 20 and the convex layer 51. Therefore, the first electrode 41 can be reliably used as a cathode. The second electrode 42 can be reliably an anode.

The present invention is not limited to the above-described embodiment, and various modifications can be made without changing the gist of the invention.
For example, the barrier layer 50 is not limited to an insulator and may be a semiconductor. The barrier layer 50 only needs to be interposed between at least a portion between the conductive layer 20 and the first electrode 41, and does not necessarily have to be interposed between the conductive layer 20 and the electrode 41.
A plurality of embodiments may be combined with each other. For example, in the third embodiment, a p-type semiconductor nanostructure 62 may be provided on the surface of the element 1 instead of the n-type semiconductor nanostructure 61. In the fourth embodiment, instead of the p-type semiconductor nanostructure 62, an n-type semiconductor nanostructure 61 may be provided on the surface of the element 1A. In the third and fourth embodiments, the n-type semiconductor nanostructure 61 and the p-type semiconductor nanostructure 62 may be mixed on the surface of the element 1 or 1A. As the n-type semiconductor nanostructure 61, n-type GaN or the like may be used instead of zinc oxide. As the p-type semiconductor nanostructure 62, p-type GaN or the like may be used instead of carbon. The polarity determination structure of the fifth embodiment (FIG. 7) may be applied to the second to fourth embodiments (FIGS. 4 to 6). In the p-type photoelectric conversion element 1 </ b> A, when the convex layer 51 is provided instead of the barrier layer 50, holes generated between the conductive layer 20 and the convex layer 51 flow to the convex layer 51 side and thus to the first electrode 41. Therefore, the first electrode 41 can be an anode and the second electrode 42 can be a cathode.
The metal component constituting the conductive layer 20 is not limited to Co, but may be Fe, W, Ni, Al, Ti, or the like.
The metal component constituting the metal nanostructure 30 is not limited to Au, and may be Ag, Pt, Cu, Pd, or the like.
The manufacturing steps of the photoelectric conversion elements 1 and 1A may be changed or changed as appropriate.

Examples will be described. Needless to say, the present invention is not limited to the following examples.
In Example 1, fabrication and observation of metal nanostructures were performed. The metal nanostructure was produced as follows.
A Co film was formed on the entire surface of a substantially square n-type Si substrate by sputtering. The thickness of the Co film was 8 nm.
Next, after organic cleaning for 5 minutes, mask printing was performed, and Au films having a thickness were formed by sputtering at the four corners and the center of the surface of the Co film. The thickness of the Au film was about 10 nm.
Next, annealing treatment was performed. The atmosphere gas for the annealing treatment was He 100%. The annealing temperature was 600 ° C. The annealing time was 3 minutes.
By annealing, Co diffused in the surface layer portion of the n-type Si substrate to form CoSix.

  Two places in the vicinity of the Au film were observed with an SEM (scanning electron microscope). FIGS. 8A and 8B show the images. It was confirmed that the fine particles of the Au film diffused along the surface of the CoSix film, and a metal nanostructure was naturally formed around the Au film. The morphology of the metal nanostructure was different depending on the location. As shown in FIG. 2B, a fractal structure was formed in the metal nanostructure depending on the location.

Laser light (wavelength 635nm) is irradiated to several points of the metal nanostructure, and the surface structure at the point where the photo-induced current at zero bias is maximized is observed three-dimensionally with an AFM (Atomic Force Microscope). did.
FIG. 9 shows the image. FIG. 10 duplicates and explains the image of FIG.
Sub-order or nano-order irregularities were formed on the surface of the metal nanostructure, and a cluster structure or fractal structure was confirmed. Furthermore, a large number of periodic structures 33 and a large number of second convex portions 32 were confirmed in the above-described uneven shape. Each periodic structure 33 includes a plurality of first protrusions 31, and the first protrusions 31 are arranged at random periods (arrangement intervals) according to the periodic structure 33. The period of the periodic structure 33 was approximately 100 nm or less. The protrusion height of each first protrusion 31 was about 10 nm to 20 nm. Each of the second convex portions 32 is disposed so as to overlap with a certain periodic structure 33 or is disposed in the vicinity of the periodic structure 33. The protrusion height of the second protrusion 32 was larger than the protrusion height of the first protrusion 31 and was about 50 nm to 200 nm. The dispersion interval of the second protrusions 32 was approximately 2 μm to 3 μm.

  The present invention is applicable to, for example, an optical sensor and a solar cell.

1, 1A Photoelectric conversion element 11 n-type semiconductor layer 12 p-type semiconductor layer 20 conductive layer 30 metal nanostructure 31 first convex portion 32 second convex portion 33 periodic structure 41 first electrode 42 second electrode 50 barrier layer (determined polarity) layer)
51 Convex layer (polarity determination layer)
61 ZnO nanowire (n-type semiconductor nanostructure)
62 Carbon nanotube (p-type semiconductor nanostructure)

Claims (6)

an n-type or p-type semiconductor layer;
A conductive layer laminated on the semiconductor layer;
A first electrode provided on the conductive layer;
A barrier layer interposed between the first electrode and the conductive layer and having a thickness that allows photocarriers to pass through the tunnel effect ;
A second electrode provided on the conductive layer apart from the first electrode ;
A metal nanostructure including a plurality of periodic structures stacked on the conductive layer;
The photoelectric conversion element is characterized in that each periodic structure includes a plurality of first protrusions protruding in the stacking direction, and an arrangement interval of the first protrusions varies depending on the periodic structure. The photoelectric conversion element according to claim 1, wherein the barrier layer is formed of an insulator having a thickness of less than 1 nm.   The at least one of the periodic structures has an arrangement interval that is 0.1 to 1 times larger than an arbitrary wavelength within a certain wavelength range from a visible light region to an infrared light region. 2. The photoelectric conversion element according to 2.   The metal nanostructure further includes a plurality of second protrusions protruding in the stacking direction from the first protrusions, the second protrusions are dispersed from each other, and each second protrusion is formed of the periodic structure. The photoelectric conversion element according to any one of claims 1 to 3, wherein the photoelectric conversion element is disposed so as to overlap with or be close to any one of them.   The photoelectric structure according to any one of claims 1 to 4, wherein a nanostructure made of a semiconductor having sensitivity in an ultraviolet region or an infrared region is provided on a surface of the conductive layer or the surface of the metal nanostructure. Conversion element.   The photoelectric conversion element according to claim 5, wherein the nanostructure is a nanowire, a nanotube, a nanoneedle, or a nanorod.