Photoelectric conversion element

Abstract

To provide a photoelectric conversion element which has a high photoelectric conversion characteristic in an ultraviolet light region and a visible light region in sunlight, and can reduce a series resistance.SOLUTION: A photoelectric conversion element comprises: a photoelectric converter where an n-type semiconductor layer; a multiple quantum well layer; and a p-type semiconductor layer are laminated in this order. In the photoelectric converter, an external light is incident from the n-type semiconductor layer, and the n-type semiconductor layer and the p-type semiconductor layer contain a nitride gallium. The multiple quantum well layer is formed by laminating one or more pairs of a quantum well layer containing an indium gallium nitride and an interference wall layer containing the gallium nitride, and overlaps the p-type semiconductor layer to form a p-side electrode layer which has a shield factor of the light incident of 7.7% or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a photoelectric conversion device using multiple quantum wells.

Background Art

[0002] As a photoelectric conversion device used in solar cells and the like, a structure using quantum wells has been proposed (see, for example, Non-Patent Document 1). This photoelectric conversion device includes, for example, a multiple quantum well (MQW) layer in which an InGaN film (quantum well film) and a GaN film (barrier film) are alternately stacked. By forming such an MQW layer, not only light corresponding to the bandgap of the semiconductor material forming the pn junction without reducing the open-circuit voltage, but also light corresponding to the bandgap of the semiconductor material forming the well layer and between the subbands formed in the well layer can be used for photoelectric conversion. Therefore, since sunlight on the long-wavelength side contributes to the photoelectric effect, a photoelectric conversion device with improved spectral sensitivity characteristics and high output can be realized.

[0003] However, a conventional photoelectric conversion device having such an MQW layer targets low-intensity light as incident light. For example, a high-intensity laser light (for example, an output of 500 mW / cm 2 or more and a wavelength of 400 nm or less) expected for next-generation power transmission is considered difficult to apply to a nitride semiconductor photoelectric conversion device for optical wireless power feeding that performs photoelectric conversion by irradiating such light.

[0004] The first is that the outermost p-type GaN layer has a high resistance as a material property (sheet resistance of about 1×10 5 Ω), which is several hundred times the resistance value of gallium arsenide-based materials. Therefore, the series resistance of the photoelectric conversion device increases. As a result, the Joule heat loss due to the large current generated when high-intensity light is incident increases, and the photoelectric conversion efficiency is significantly reduced.

[0005] That is, when hole carriers are transported to the electrode layer, if the hole carriers move laterally inside the high-resistance p-type GaN layer, significant resistance losses will occur. Therefore, by forming ITO as the transparent electrode on the top, a method of reducing resistance losses is often adopted by having the lateral movement of hole carriers occur inside the ITO. However, the contact resistance of ITO with the p-type GaN layer is about 1000 times greater than the contact resistance value of a normal ohmic electrode (for example, 1×10 -2 Ωcm 2 ~1×10 -5 Ωcm 2 or so), for example, 10Ωcm 2 ~1×10 -2 Ωcm 2 or so. Therefore, the effect of introducing ITO is limited.

[0006] In addition, the light transmittance of ITO in the ultraviolet region is low. For example, the transmission loss rate of ultraviolet light with a wavelength of 395 nm is as high as 3.4%, 4.9%, and 6.4% when the film thickness of ITO is 30 nm, 40 nm, and 50 nm, respectively. In applications of optical wireless power supply systems where a photoelectric conversion efficiency exceeding 50% is required, it is necessary to reduce the film thickness of ITO to 30 nm or less. At such thicknesses, sufficient conductivity cannot be ensured as an electrode.

[0007] Second, although InGaN (indium gallium nitride) is adopted for the quantum well films of the MQW layer, the light absorption coefficient of InGaN is about 1×10 5 cm -1 or so. To absorb laser light with a wavelength near 400 nm such as ultraviolet light, the total film thickness of the MQW layer needs to be 400 nm or more. However, if the InGaN layer with a larger lattice than the GaN layer is made thick, the lattice strain becomes large and crystal defects are likely to occur. Therefore, it is difficult to increase the thickness of the InGaN layer.

[0008] For example, in Non-Patent Document 1, since the total film thickness of the MQW layer is extremely thin at 17.5 nm, external light, such as sunlight, cannot be sufficiently absorbed, and the photoelectric conversion efficiency is extremely low at about 0.6%. Also, in Non-Patent Document 2, since the total film thickness of the MQW layer is thin at 121.8 nm, only about 70% of the incident laser light is absorbed, and there are still issues with the photoelectric conversion efficiency.

Prior Art Documents

Non-Patent Documents

[0009]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0010] The present invention has been made in view of the above problems, and an object thereof is to provide a photoelectric conversion element having high photoelectric conversion characteristics in the ultraviolet and visible light regions of sunlight and capable of reducing series resistance.

Means for Solving the Problems

[0011] One embodiment of the photoelectric conversion device of the present invention proposes the following means. (1) The photoelectric conversion device according to Aspect 1 of the present invention has a photoelectric conversion body in which an n-type semiconductor layer, a multiple quantum well layer, and a p-type semiconductor layer are laminated in this order. External light is incident on the photoelectric conversion body from the n-type semiconductor layer side. The n-type semiconductor layer and the p-type semiconductor layer contain gallium nitride, and the multiple quantum well layer is formed by laminating one or more pairs of a quantum well layer containing indium gallium nitride and a barrier layer containing gallium nitride. A p-side electrode layer having a light shielding rate of 7.7% or more for the incident light is formed on the p-type semiconductor layer.

[0012] (2) Aspect 2 of the present invention is characterized in that, in the photoelectric conversion device of Aspect 1, the p-side electrode layer has a light shielding rate of 99% or more for the incident light.

[0013] (3) Aspect 3 of the present invention is the photoelectric conversion device according to Aspect 1 or 2, wherein the p-side electrode layer has a reflectance of 50% or more for light in the ultraviolet wavelength range, and a contact resistance value of 1×10 -5 Ωcm 2 or more and 1×10 -2 Ωcm 2 or less. The photoelectric conversion device according to claim 2 is characterized by the above.

[0014] (4) Aspect 4 of the present invention is the photoelectric conversion device according to any one of Aspects 1 to 3, wherein the p-side electrode layer has a p-side first region and a p-side second region. The p-side first region has a lower contact resistance value than the p-side second region, and the p-side second region has a higher reflectance for light in the ultraviolet wavelength range than the p-side first region. When the p-side electrode layer is viewed in plan from one surface side, the area of the p-side second region is larger than that of the p-side first region.

[0015] (5)Aspect 5 of the present invention is the photoelectric conversion element of Aspect 4, wherein the p-side first region is composed of any one of a Ni / Au laminated film, a Pd / Au laminated film, a Pt film, a Pd / Pt laminated film, and a Rh / Au laminated film, and the p-side second region is composed of any one of an Ag film, an Ag / Cu laminated film, a Mg film, an ITO / Ag laminated film, an Ag / La laminated film, a Cu-doped In2O3 film, and a Ni / Au / W / Ag laminated film.

[0016] (6)Aspect 6 of the present invention is the photoelectric conversion element of Aspect 4, wherein the p-side first region is composed of any one of a Ni / Au laminated film, a Pd / Au laminated film, a Pt film, a Pd / Pt laminated film, and a Rh / Au laminated film, and the p-side second region is composed of any one of a TiO2 / SiO2 laminated film, a TiO2 / Al2O3 laminated film, a ZrO2 / SiO2 laminated film, a ZrO2 / Al2O3 laminated film, a Ta2O5 / SiO2 laminated film, and a Ta2O5 / Al2O3 laminated film.

[0017] (7)Aspect 7 of the present invention is the photoelectric conversion element of any one of Aspects 1 to 6, wherein a low reflection layer having a reflectivity of 10% or less with respect to incident external light is formed on the n-type semiconductor layer.

[0018] (8)Aspect 8 of the present invention is the photoelectric conversion element of Aspect 7, wherein the low reflection layer is composed of any one of an Al2O3 film, an SiO2 film, a LiF film, a LiF / SiO2 laminated film, a LiF / Al2O3 laminated film, an SiO2 / Al2O3 laminated film, a LiF / SiO2 / Al2O3 laminated film, an SiO2 / TiO2 laminated film, an SiO2 / Ta2O5 laminated film, an SiO2 / ZrO2 laminated film, an Al2O3 / TiO2 laminated film, an Al2O3 / Ta2O5 laminated film, and an Al2O3 / ZrO2 laminated film.

[0019] (9)Aspect 9 of the present invention is an optoelectronic conversion element according to any one of Aspects 1 to 8, in which an n-side electrode layer is formed on top of the n-type semiconductor layer. The n-side electrode layer has an n-side first region and an n-side second region. The contact resistance value of the n-side first region is lower than that of the n-side second region. The reflectance of the n-side second region with respect to incident external light is lower than that of the n-side first region. When the n-side electrode layer is viewed in plan from one surface side, the area of the n-side second region is larger than that of the n-side first region.

[0020] (10)Aspect 10 of the present invention is the optoelectronic conversion element according to Aspect 9, in which the n-side first region is composed of any one of a Ti / Al laminated film, a Ti / Al / Ni / Au laminated film, a Ti / Al / Ti / Au laminated film, and a Ti / Al / Ti / Pt / Au laminated film. The n-side second region is composed of any one of an Al2O3 film, an SiO2 film, a LiF film, a LiF / SiO2 laminated film, a LiF / Al2O3 laminated film, an SiO2 / Al2O3 laminated film, a LiF / SiO2 / Al2O3 laminated film, an SiO2 / TiO2 laminated film, an SiO2 / Ta2O5 laminated film, an SiO2 / ZrO2 laminated film, an Al2O3 / TiO2 laminated film, an Al2O3 / Ta2O5 laminated film, and an Al2O3 / ZrO2 laminated film.

[0021] (11)Aspect 11 of the present invention is the optoelectronic conversion element according to Aspect 10, in which the n-side second region is formed by laminating any one of an Al2O3 film, an SiO2 film, a LiF film, a LiF / SiO2 laminated film, a LiF / Al2O3 laminated film, an SiO2 / Al2O3 laminated film, a LiF / SiO2 / Al2O3 laminated film, an SiO2 / TiO2 laminated film, an SiO2 / Ta2O5 laminated film, an SiO2 / ZrO2 laminated film, an Al2O3 / TiO2 laminated film, an Al2O3 / Ta2O5 laminated film, and an Al2O3 / ZrO2 laminated film with a transparent conductive film made of any one of ITO, ZnO, SnO2, In2O3, and AZO.

[0022] (12) The photoelectric conversion element according to Embodiment 12 of the present invention has a photoelectric conversion body in which an n-type semiconductor layer, a multiple quantum well layer, and a p-type semiconductor layer are laminated in this order. In the photoelectric conversion body, external light is incident from the p-type semiconductor layer side. The n-type semiconductor layer and the p-type semiconductor layer contain gallium nitride, and the multiple quantum well layer is formed by laminating one or more pairs of a quantum well layer containing indium gallium nitride and a barrier layer containing gallium nitride. A reflective layer is formed on top of the n-type semiconductor layer.

[0023] (13) Embodiment 13 of the present invention is the photoelectric conversion element according to Embodiment 12, characterized in that the reflective layer is composed of any one of an Ag film, an Ag / Cu laminated film, an Mg film, an ITO / Ag laminated film, an Ag / La laminated film, a Cu-doped In2O3 film, and a Ni / Au / W / Ag laminated film.

[0024] (14) Embodiment 14 of the present invention is the photoelectric conversion element according to Embodiment 12, characterized in that the reflective layer is a dielectric and is composed of any one of a TiO2 / SiO2 laminated film, a TiO2 / Al2O3 laminated film, a ZrO2 / SiO2 laminated film, a ZrO2 / Al2O3 laminated film, a Ta2O5 / SiO2 laminated film, and a Ta2O5 / Al2O3 laminated film.

[0025] (15) Embodiment 15 of the present invention is the photoelectric conversion element according to Embodiment 12, characterized in that the reflective layer is an n-side electrode layer. The n-side electrode layer has an n-side first region and an n-side second region. The n-side first region is composed of any one of a Ti / Al laminated film, a Ti / Al / Ni / Au laminated film, a Ti / Al / Ti / Au laminated film, and a Ti / Al / Ti / Pt / Au laminated film. The n-side second region is composed of any one of a TiO2 / SiO2 laminated film, a TiO2 / Al2O3 laminated film, a ZrO2 / SiO2 laminated film, a ZrO2 / Al2O3 laminated film, a Ta2O5 / SiO2 laminated film, and a Ta2O5 / Al2O3 laminated film.

Advantages of the Invention

[0026] According to the present invention, it becomes possible to provide a photoelectric conversion element having high photoelectric conversion characteristics in the ultraviolet light region and the visible light region of sunlight and capable of reducing the series resistance.

Brief Description of Drawings

[0027]

Figure 1

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Figure 10

Embodiments for Carrying Out the Invention

[0028] Hereinafter, with reference to the drawings, photoelectric conversion elements according to some embodiments of the present invention will be described. Each of the embodiments described below is specifically described to better understand the gist of the invention, and does not limit the present invention unless otherwise specified. In addition, the drawings used in the following description may show the main parts enlarged for convenience of clearly understanding the features of the present invention, and the dimensional ratios of each component are not necessarily the same as the actual ones.

[0029] (First Embodiment) FIG. 1 is a schematic cross-sectional view showing the configuration of a photoelectric conversion element according to the first embodiment of the present invention. The photoelectric conversion element 10 of the present embodiment is formed in order from the incident side of external light with a light-transmissive substrate 11, a photoelectric conversion body 12, a p-side electrode layer 13, and a mount portion 14 in this order.

[0030] One side of the light-transmissive substrate 11 forms an incident surface for allowing external light, for example, sunlight, to enter the photoelectric conversion element 10. Such a light-transmissive substrate 11 can be a substrate that can transmit the incident external light, for example, a sapphire (Al2O3) substrate or a gallium nitride (GaN) substrate.

[0031] The photoelectric conversion body 12 is a layer that absorbs the incident external light and performs photoelectric conversion. The photoelectric conversion body 12 is formed by laminating an n-type semiconductor layer 15, a multiple quantum well layer 16, and a p-type semiconductor layer 17 in this order. In the present embodiment, the n-type semiconductor layer 15 side of the photoelectric conversion body 12 is the light incident side. The n-type semiconductor layer 15 is formed from gallium nitride (GaN) that forms an n-type semiconductor.

[0032] The multiple quantum well layer 16 is formed by laminating one or more pairs of, for example, a quantum well layer 16a containing indium gallium nitride (InGaN) and a barrier layer 16b containing gallium nitride (GaN). The thickness of such a multiple quantum well layer 16 is generally in the range of about 5 nm to 20 nm.

[0033] The p-type semiconductor layer 17 is formed from gallium nitride (GaN) that forms a p-type semiconductor. The p-side electrode layer 13 is formed in contact with the p-type semiconductor layer 17 of the photoelectric converter 12. The p-side electrode layer 13 is made of a material with a shielding rate, which is the ratio of shielding light, of 7.7% or more, for example 100%, when the amount of light incident through the photoelectric converter 12 is set to 100. A lead-out electrode 5A is formed in contact with such a p-side electrode layer 13.

[0034] An n-side electrode layer 18 is formed at one end of the n-type semiconductor layer 15 constituting the photoelectric converter 12. Such an n-side electrode layer 18 is connected to the lead-out electrode 5B via a conductor 19 for the purpose of step correction with the mount portion 14.

[0035] The mount portion 14 is made of, for example, a dielectric material and forms a substrate that supports the entire photoelectric conversion element 10. When external light, for example sunlight, is incident on such a photoelectric conversion element 10, photoelectric conversion is performed by the photoelectric converter 12, and electric power is extracted between the lead-out electrode 5A and the lead-out electrode 5B.

[0036] According to the photoelectric conversion element 10 of the present embodiment configured as described above, in a photoelectric conversion element having a multiple quantum well structure using a nitride semiconductor, the photoelectric conversion efficiency in a wide wavelength range of sunlight, particularly in the ultraviolet light region, can be greatly improved.

[0037] Conventional photoelectric conversion elements and solar cells using nitride semiconductors had high element resistance and low light absorption efficiency, so the photoelectric conversion efficiency was several percent or less. Even when used for optical wireless power feeding applications, the photoelectric conversion efficiency was 25% or less.

[0038] On the one hand, by using the photoelectric conversion element 10 configured in this embodiment, external light that has passed through the photoelectric conversion body 12 without being absorbed and photoelectrically converted and has transmitted to the p-type semiconductor layer 17 side can be reflected to the photoelectric conversion body 12 side by a reflection structure (photon recycling effect) having a shielding rate of 7.7% or more, for example, 100%, and can be recombined by the p-side electrode layer 13. As a result, the fill factor FF reflecting the element resistance is 30 to 60% in a conventional photoelectric conversion element, whereas in the photoelectric conversion element 10 of this embodiment, it can be increased to about 60 to 90%, and excellent photoelectric conversion characteristics can be realized. In addition, the short-circuit current density also increases by 1.3 to 1.4 times more than before due to the increase in the light absorption amount of the photoelectric conversion body 12, and a significant improvement in the photoelectric conversion efficiency can be achieved.

[0039] (Second Embodiment) FIG. 2 is a schematic cross-sectional view showing the configuration of the photoelectric conversion element according to the second embodiment of the present invention. Note that the same components as those of the photoelectric conversion element of the first embodiment described above are denoted by the same reference numerals, and redundant descriptions are omitted. In the photoelectric conversion element 20 of this embodiment, a highly reflective metal film is used as the p-side electrode layer 23. As a result, the p-side electrode layer 23 has a reflectivity of 50% or more with respect to light in the ultraviolet wavelength range and a contact resistance value of 1×10 -5 Ωcm 2 or more and 1×10 -2 Ωcm 2 or less.

[0040] As a specific example of the constituent material of the p-side electrode layer 23, it may be constituted by any one of an Ag film, an Ag-Cu alloy film, an Mg film, an ITO / Ag laminated film, an Ag / La laminated film, a Cu-doped In2O3 film, and a Ni / Au / W / Ag laminated film. Note that in this embodiment and each of the following embodiments, the notation X1 / X2 laminated film indicates that a film of material X1 and a film of material X2 are laminated along the lamination direction of the photoelectric conversion element 20.

[0041] According to the present embodiment, by using a metal film as the p-side electrode layer 23, the reflectance of external light transmitted through the photoelectric conversion body 12 can be increased to promote recombination in the photoelectric conversion body 12, and as an electrode, the resistance can be lowered and the conductivity can be increased, thereby reducing the power loss at the electrode.

[0042] (Third Embodiment) FIG. 3 is a schematic cross-sectional view showing the configuration of the photoelectric conversion element according to the third embodiment of the present invention. Note that the same components as those of the photoelectric conversion element of the first embodiment described above are denoted by the same reference numerals, and redundant descriptions are omitted. In the photoelectric conversion element 30 of the present embodiment, the p-side electrode layer 33 has a p-side first electrode region (p-side first region) 33a and a p-side second electrode region (p-side second region) 33b.

[0043] For example, when the p-side electrode layer 33 is viewed in plan from above, the p-side first electrode region 33a and the p-side second electrode region 33b may be formed so as to be partitioned in a stripe shape. Further, the total area occupied by the p-side second electrode region 33b may be larger than the total area occupied by the p-side first electrode region 33a. As an example, the area ratio (shielding ratio) occupied by the p-side first electrode region 33a may be in the range of 7.7% to 20%, and the area ratio occupied by the p-side second electrode region 33b may be in the range of 80% to 92.3%.

[0044] Such a p-side first electrode region 33a is made of a material having a lower contact resistance value than the p-side second electrode region 33b. Further, the p-side second electrode region 33b may be made of a dielectric material having a higher reflectance for light in the ultraviolet wavelength range than the p-side first electrode region 33a.

[0045] Examples of the constituent material of the p-side first electrode region 33a may be any of a Ni / Au laminated film, a Pd / Au laminated film, a Pt film, a Pd / Pt laminated film, and a Rh / Au laminated film. Further, the p-side second electrode region 33b may be any of an Ag film, an Ag / Cu laminated film, an Mg film, an ITO / Ag laminated film, an Ag / La laminated film, a Cu-doped In2O3 film, and a Ni / Au / W / Ag laminated film.

[0046] As in this embodiment, by partitioning the p-side electrode layer 33 into regions made of two different materials, namely the p-side first electrode region (p-side first region) 33a and the p-side second electrode region (p-side second region) 33b, the reflectivity of external light transmitted through the photoelectric conversion body 12 can be increased to promote recombination in the photoelectric conversion body 12, and at the same time, two functions such as reducing the power loss at the electrode by making the electrode have low resistance and high conductivity can be achieved simultaneously.

[0047] (Fourth Embodiment) FIG. 4 is a schematic cross-sectional view showing the configuration of the photoelectric conversion element according to the fourth embodiment of the present invention. Note that the same components as those of the photoelectric conversion element of the first embodiment described above are denoted by the same reference numerals, and redundant descriptions are omitted. In the photoelectric conversion element 40 of this embodiment, the p-side electrode layer 43 has a p-side electrode region (p-side first region) 43a and a p-side dielectric region (p-side second region) 43b.

[0048] For example, when the p-side electrode layer 43 is viewed in plan from above, the p-side electrode region 43a and the p-side dielectric region 43b may be formed so as to be partitioned in a stripe shape. Also, the total area occupied by the p-side dielectric region 43b may be larger than the total area occupied by the p-side electrode region 43a. As an example, the area ratio (shielding ratio) occupied by the p-side electrode region 43a may be in the range of 7.7% to 20%, and the area ratio occupied by the p-side dielectric region 43b may be in the range of 80% to 92.3%.

[0049] Such a p-side electrode region 43a is composed of a material having a lower contact resistance value than the p-side dielectric region 43b. Also, the p-side dielectric region 43b may be composed of a dielectric material having a higher reflectivity for light in the ultraviolet wavelength range than the p-side electrode region 43a.

[0050] As an example of the constituent material of the p-side electrode region 43a, it may be composed of any one of a Ni / Au laminated film, a Pd / Au laminated film, a Pt film, a Pd / Pt laminated film, and a Rh / Au laminated film. Further, the p-side dielectric region 43b may be composed of any one of a TiO2 / SiO2 laminated film, a TiO2 / Al2O3 laminated film, a ZrO2 / SiO2 laminated film, a ZrO2 / Al2O3 laminated film, a Ta2O5 / SiO2 laminated film, and a Ta2O5 / Al2O3 laminated film.

[0051] As in the present embodiment, by partitioning the p-side electrode layer 43 into regions made of two different materials, namely, the p-side electrode region (p-side first region) 43a and the p-side dielectric region (p-side second region) 43b, it is possible to enhance the reflectivity of external light transmitted through the photoelectric conversion element 12 and promote recombination in the photoelectric conversion element 12, and at the same time, achieve both effects of reducing the resistance as an electrode and enhancing conductivity to reduce power loss at the electrode.

[0052] (Fifth Embodiment) FIG. 5 is a schematic cross-sectional view showing the configuration of the photoelectric conversion element according to the fifth embodiment of the present invention. Note that the same components as those of the photoelectric conversion element of the first embodiment described above are denoted by the same reference numerals, and redundant descriptions are omitted. In the photoelectric conversion element 50 of the present embodiment, a low-reflection layer 51 is further formed so as to be in contact with the incident surface side of the light-transmissive substrate 11, on top of the n-type semiconductor layer 15. Such a low-reflection layer 51 may be formed of a material having a reflectivity of 10% or less with respect to incident external light. As an example of the constituent material of the low-reflection layer 51, it may be composed of any one of an Al2O3 film, an SiO2 film, a LiF film, a LiF / SiO2 laminated film, a LiF / Al2O3 laminated film, an SiO2 / Al2O3 laminated film, a LiF / SiO2 / Al2O3 laminated film, an SiO2 / TiO2 laminated film, an SiO2 / Ta2O5 laminated film, an SiO2 / ZrO2 laminated film, an Al2O3 / TiO2 laminated film, an Al2O3 / Ta2O5 laminated film, and an Al2O3 / ZrO2 laminated film.

[0053] By forming the low-reflection layer 51 on top of the n-type semiconductor layer 15 as in this embodiment, even if sapphire or GaN with a slightly high surface reflectance is used as the light-transmissive substrate 11, the loss due to surface reflection when external light enters the photoelectric conversion element 50 can be reduced, more external light can be introduced into the photoelectric conversion element 50, and the photoelectric conversion efficiency can be increased.

[0054] (Sixth Embodiment) FIG. 6 is a schematic cross-sectional view showing the configuration of the photoelectric conversion element according to the sixth embodiment of the present invention. Note that the same components as those of the photoelectric conversion element of the first embodiment described above are denoted by the same reference numerals, and redundant descriptions are omitted. In the photoelectric conversion element 60 of this embodiment, an n-side electrode layer 63 is formed so as to be in contact with the incident surface side of the light-transmissive substrate 11 on top of the n-type semiconductor layer 15 (as in the first embodiment, the n-side electrode layer 18 is not formed at one end of the n-type semiconductor layer 15). Such an n-side electrode layer 63 has an n-side electrode region (n-side first region) 63a and an n-side dielectric region (n-side second region) 63b.

[0055] For example, when the n-side electrode layer 63 is viewed in plan from above, the n-side electrode region 63a and the n-side dielectric region 63b may be formed so as to be partitioned in a stripe shape. Also, the total area occupied by the n-side dielectric region 63b may be larger than the total area occupied by the n-side electrode region 63a. As an example, the area ratio (shielding ratio) occupied by the n-side electrode region 63a may be in the range of 1% to 20%, and the area ratio occupied by the n-side dielectric region 63b may be in the range of 99% to 80%.

[0056] Such an n-side electrode region 63a is made of a material having a lower contact resistance value than the n-side dielectric region 63b. Also, the n-side dielectric region 63b may be made of a dielectric material having a high reflectance for light in the ultraviolet wavelength range.

[0057] As an example of the constituent material of the n-side electrode region 63a, it may be composed of any one of a Ti / Al laminated film, a Ti / Al / Ni / Au laminated film, a Ti / Al / Ti / Au laminated film, and a Ti / Al / Ti / Pt / Au laminated film. Further, the n-side dielectric region 63b may be composed of any one of an Al2O3 film, an SiO2 film, a LiF film, a LiF / SiO2 laminated film, a LiF / Al2O3 laminated film, an SiO2 / Al2O3 laminated film, a LiF / SiO2 / Al2O3 laminated film, an SiO2 / TiO2 laminated film, an SiO2 / Ta2O5 laminated film, an SiO2 / ZrO2 laminated film, an Al2O3 / TiO2 laminated film, an Al2O3 / Ta2O5 laminated film, and an Al2O3 / ZrO2 laminated film.

[0058] As the light-transmissive substrate 11 of the present embodiment, a gallium nitride (GaN) substrate can be applied.

[0059] As in the present embodiment, by forming the n-side electrode layer 63 having the n-side electrode region 63a and the n-side dielectric region 63b on the n-type semiconductor layer 15, even when using sapphire or GaN with a slightly high surface reflectance as the light-transmissive substrate 11, the loss due to surface reflection when external light enters the photoelectric conversion element 50 can be reduced, more external light can be introduced into the photoelectric conversion element 50, the photoelectric conversion efficiency can be increased, and as the n-side electrode, two effects such as reducing the resistance and increasing the conductivity to reduce the power loss at the electrode can be achieved simultaneously.

[0060] (Seventh Embodiment) FIG. 7 is a schematic cross-sectional view showing the configuration of the photoelectric conversion element according to the seventh embodiment of the present invention. Note that the same components as those of the photoelectric conversion element of the sixth embodiment described above are denoted by the same reference numerals, and redundant descriptions are omitted. In the photoelectric conversion element 70 of the present embodiment, the n-side electrode layer 73 has an n-side electrode region (n-side first region) 73a and an n-side dielectric region (n-side second region) 73b. And in the present embodiment, the n-side dielectric region (n-side second region) 73b is composed of an upper layer portion 73bA and a lower layer portion 73bB. As an example of the constituent material of the n-side electrode region 73a, the same material as the n-side electrode region 63a of the sixth embodiment can be used.

[0061] As an example of the constituent material of the upper layer portion 73bA of the n-side dielectric region 73b, it may be composed of any one of an Al2O3 film, an SiO2 film, a LiF film, a LiF / SiO2 laminated film, a LiF / Al2O3 laminated film, an SiO2 / Al2O3 laminated film, and a LiF / SiO2 / Al2O3 laminated film. Further, as an example of the constituent material of the lower layer portion 73bB, it may be composed of any one of ITO, ZnO, SnO2, In2O3, and AZO (Al doped Zinc Oxide).

[0062] As the light-transmissive substrate 11 of the present embodiment, a gallium nitride (GaN) substrate can be applied.

[0063] As in the present embodiment, by forming the n-side dielectric region 73b from the upper layer portion 73bA and the lower layer portion 73bB, a conductor region is formed under the n-side dielectric region, and the conductivity as the n-side electrode can be further enhanced to reduce the power loss at the electrode.

[0064] (Eighth Embodiment) FIG. 8 is a schematic cross-sectional view showing the configuration of the photoelectric conversion element according to the first embodiment of the present invention. In the photoelectric conversion element 80 of the present embodiment, a p-side electrode layer 83, a photoelectric conversion body 82, a light-transmissive substrate 81, and a metal reflection layer (reflection layer) 84 are sequentially formed in this order from the incident side of external light.

[0065] One side of the p-side electrode layer 83 forms an incident surface for allowing external light, for example, sunlight, to enter the photoelectric conversion element 80. Such a p-side electrode layer 83 may be composed of a transparent conductive material, for example, ITO, ZnO, SnO2, In2O3, AZO, or the like.

[0066] The photoelectric conversion body 82 is a layer that absorbs incident external light and performs photoelectric conversion. The photoelectric conversion body 82 is formed by laminating a p-type semiconductor layer 85, a multiple quantum well layer 86, and an n-type semiconductor layer 87 in this order. In the present embodiment, the p-type semiconductor layer 85 side of the photoelectric conversion body 82 is the light incident side.

[0067] The p-type semiconductor layer 85 is formed from gallium nitride (GaN) that forms a p-type semiconductor. The multiple quantum well layer 86 is formed by laminating one or more pairs of, for example, a quantum well layer 86a containing indium gallium nitride (InGaN) and a barrier layer 86b containing gallium nitride (GaN). The thickness of such a multiple quantum well layer 16 generally may be in the range of about 2 nm to 20 nm. The n-type semiconductor layer 87 is formed from gallium nitride (GaN) that forms an n-type semiconductor.

[0068] An n-side electrode layer 88 is formed at one end of the n-type semiconductor layer 87 that constitutes the photoelectric conversion body 82.

[0069] As the light-transmissive substrate 81, for example, a sapphire (Al2O3) substrate or a gallium nitride (GaN) substrate can be applied.

[0070] The metal reflection layer (reflection layer) 84 is formed in contact with the light-transmissive substrate 81, overlapping the n-type semiconductor layer 87. In the photoelectric conversion element 80 of the present embodiment, a highly reflective metal film is used as the metal reflection layer 84. As a specific example of the constituent material of the metal reflection layer 84, it may be composed of any one of an Ag film, an Ag-Cu alloy film, an Mg film, an ITO / Ag laminated film, an Ag / La laminated film, a Cu-doped In2O3 film, and a Ni / Au / W / Ag laminated film.

[0071] According to the photoelectric conversion element 80 of the present embodiment, even in a configuration where external light, such as sunlight, is incident on the photoelectric conversion element 80 from the p-side electrode layer 83 side, by forming the metal reflection layer 84 on top of the n-type semiconductor layer 87, the reflectivity of the external light transmitted through the photoelectric conversion body 82 is increased to promote recombination in the photoelectric conversion body 82. Thereby, in a photoelectric conversion element having a multiple quantum well structure using a nitride semiconductor, the photoelectric conversion efficiency in a wide wavelength range of sunlight, particularly in the ultraviolet light region, can be greatly improved.

[0072] (Embodiment 9) FIG. 9 is a schematic cross-sectional view showing the configuration of the photoelectric conversion element of the ninth embodiment of the present invention. Note that the same components as those of the photoelectric conversion element of the eighth embodiment described above are denoted by the same reference numerals, and redundant descriptions are omitted. In the photoelectric conversion element 90 of the present embodiment, a dielectric reflection layer (reflection layer) 94 is formed on top of the n-type semiconductor layer 87 so as to be in contact with the light-transmissive substrate 81. Specific examples of the constituent material of the dielectric reflection layer 94 may be any of a TiO2 / SiO2 laminated film, a TiO2 / Al2O3 laminated film, a ZrO2 / SiO2 laminated film, a ZrO2 / Al2O3 laminated film, a Ta2O5 / SiO2 laminated film, and a Ta2O5 / Al2O3 laminated film.

[0073] According to the photoelectric conversion element 90 of the present embodiment, even in a configuration where external light, such as sunlight, is incident on the photoelectric conversion element 90 from the p-side electrode layer 83 side, by forming the dielectric reflection layer (reflection layer) 94 on top of the n-type semiconductor layer 87, the reflectivity of the external light transmitted through the photoelectric conversion body 82 is increased to promote recombination in the photoelectric conversion body 82. Thereby, in a photoelectric conversion element having a multiple quantum well structure using a nitride semiconductor, the photoelectric conversion efficiency in a wide wavelength range of sunlight, particularly in the ultraviolet light region, can be greatly improved.

[0074] (Embodiment 10) FIG. 10 is a schematic cross-sectional view showing the configuration of the photoelectric conversion element of the tenth embodiment of the present invention. Note that the same components as those of the photoelectric conversion element of the eighth embodiment described above are denoted by the same reference numerals, and redundant descriptions are omitted. In the photoelectric conversion element 100 of this embodiment, an n-side electrode layer (reflective layer) 104 is formed so as to be in contact with the light-transmissive substrate 81, overlapping the n-type semiconductor layer 87 (unlike the eighth embodiment, the n-side electrode layer 88 is not formed at one end of the n-type semiconductor layer 87). Such an n-side electrode layer (reflective layer) 104 has an n-side electrode region (n-side first region) 104a and an n-side dielectric region (n-side second region) 104b.

[0075] For example, when the n-side electrode layer 104 is viewed in plan from above, the n-side electrode region 104a and the n-side dielectric region 104b may be formed so as to be partitioned in a stripe shape. Further, the total area occupied by the n-side dielectric region 104b may be larger than the total area occupied by the n-side electrode region 104a. As an example, the area ratio (shielding ratio) occupied by the n-side electrode region 104a may be in the range of 1% to 20%, and the area ratio occupied by the n-side dielectric region 104b may be in the range of 99% to 80%.

[0076] Such an n-side electrode region 104a is made of a material having a lower contact resistance value than the n-side dielectric region 104b. Further, the n-side dielectric region 104b may be made of a dielectric material having a high reflectance for light in the ultraviolet wavelength range.

[0077] Examples of the constituent material of the n-side electrode region 104a may be any of a Ti / Al laminated film, a Ti / Al / Ni / Au laminated film, a Ti / Al / Ti / Au laminated film, and a Ti / Al / Ti / Pt / Au laminated film. Further, the n-side dielectric region 104b may be made of any of a TiO2 / SiO2 laminated film, a TiO2 / Al2O3 laminated film, a ZrO2 / SiO2 laminated film, a ZrO2 / Al2O3 laminated film, a Ta2O5 / SiO2 laminated film, and a Ta2O5 / Al2O3 laminated film.

[0078] According to the photoelectric conversion element 100 of the present embodiment, even when external light, for example, sunlight, is incident on the photoelectric conversion element 100 from the p-side electrode layer 83 side, by forming the n-side electrode layer (reflective layer) 104 on top of the n-type semiconductor layer 87, the reflectivity of the external light transmitted through the photoelectric conversion body 82 is increased to promote recombination in the photoelectric conversion body 82. As a result, in a photoelectric conversion element having a multiple quantum well structure using a nitride semiconductor, the photoelectric conversion efficiency in a wide wavelength range of sunlight, particularly in the ultraviolet light region, can be greatly improved.

[0079] As described above, the embodiments of the present invention have been explained. However, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and its equivalent scope.

Industrial Applicability

[0080] According to the photoelectric conversion element of the present invention, a photoelectric conversion element having high photoelectric conversion characteristics in the ultraviolet light region and visible light region of sunlight and capable of reducing the series resistance is realized, and using this, it contributes to realizing a solar cell with high power generation efficiency. Therefore, the present invention has industrial applicability.

Explanation of Reference Numerals

[0081] 10… Photoelectric conversion element 11… Light-transmissive substrate 12… Photoelectric conversion body 13… p-side electrode layer 15… n-type semiconductor layer 16… Multiple quantum well layer 17… p-type semiconductor layer 18… n-side electrode layer

Claims

1. A photoelectric conversion element having an n-type semiconductor layer, a multiple quantum well layer, and a p-type semiconductor layer laminated in this order, wherein external light is incident on the photoelectric conversion element from the n-type semiconductor layer side, the n-type semiconductor layer and the p-type semiconductor layer contain gallium nitride, the multiple quantum well layer is formed by laminating one or more pairs of a quantum well layer containing indium gallium nitride and a barrier layer containing gallium nitride, and a p-side electrode layer having a light shielding rate of 7.7% or more for incident light is formed on the p-type semiconductor layer. A photoelectric conversion element characterized by this.

2. The p-side electrode layer has a light shielding rate of 99% or more for incident light. The photoelectric conversion element according to Claim 1, characterized by this.

3. The p-side electrode layer has a reflectance of 50% or more with respect to light in the ultraviolet wavelength range, and a contact resistance value of 1×10 －５ Ωcm ２ or more and 1×10 －２ Ωcm ２ or less, and is the photoelectric conversion element according to claim 2, characterized in that.

4. The p-side electrode layer has a p-side first region and a p-side second region, the p-side first region has a lower contact resistance value than the p-side second region, the p-side second region has a higher reflectance for light in the ultraviolet wavelength range than the p-side first region, and when the p-side electrode layer is viewed in plan from one surface side, the area of the p-side second region is larger than the area of the p-side first region. The photoelectric conversion element according to Claim 1, characterized by this.

5. The p-side first region is composed of any one of a Ni / Au laminated film, a Pd / Au laminated film, a Pt film, a Pd / Pt laminated film, and a Rh / Au laminated film, The p-side second region is composed of any one of an Ag film, an Ag / Cu laminated film, a Mg film, an ITO / Ag laminated film, an Ag / La laminated film, and a Cu-doped In ２ O ３ film, and a Ni / Au / W / Ag laminated film. The photoelectric conversion element according to claim 4, characterized in that.

6. The p-side first region is composed of any one of a Ni / Au laminated film, a Pd / Au laminated film, a Pt film, a Pd / Pt laminated film, and a Rh / Au laminated film, The p-side second region is TiO ２ / SiO ２ laminated film, TiO ２ / Al ２ O ３ laminated film, ZrO ２ / SiO ２ laminated film, ZrO ２ / Al ２ O ３ laminated film, Ta ２ O ５ / SiO ２ laminated film, Ta ２ O ５ / Al ２ O ３ The photoelectric conversion element according to claim 4, characterized in that it is composed of any one of the laminated films.

7. A low reflection layer having a reflectance of 10% or less for incident external light is formed on the n-type semiconductor layer. The photoelectric conversion element according to Claim 1 or 2, characterized by this.

8. The low-reflection layer is Al ２ O ３ film, SiO ２ film, LiF film, LiF / SiO ２ laminated film, LiF / Al ２ O ３ laminated film, SiO ２ / Al ２ O ３ laminated film, LiF / SiO ２ / Al ２ O ３ laminated film, SiO ２ / TiO ２ laminated film, SiO ２ / Ta ２ O ５ laminated film, SiO ２ / ZrO ２ laminated film, Al ２ O ３ / TiO ２ laminated film, Al ２ O ３ / Ta ２ O ５ laminated film, Al ２ O ３ / ZrO ２ The photoelectric conversion element according to claim 7, characterized in that it is composed of any one of the laminated films.

9. An n-side electrode layer is formed on the n-type semiconductor layer, the n-side electrode layer has an n-side first region and an n-side second region, the n-side first region has a lower contact resistance value than the n-side second region, the n-side second region has a lower reflectance for incident external light than the n-side first region, and when the n-side electrode layer is viewed in plan from one surface side, the area of the n-side second region is larger than the area of the n-side first region. The photoelectric conversion element according to Claim 1 or 2, characterized by this.

10. The n-side first region is composed of any one of a Ti / Al laminated film, a Ti / Al / Ni / Au laminated film, a Ti / Al / Ti / Au laminated film, and a Ti / Al / Ti / Pt / Au laminated film, The n-side second region is Al ２ O ３ film, SiO ２ film, LiF film, LiF / SiO ２ laminated film, LiF / Al ２ O ３ laminated film, SiO ２ / Al ２ O ３ laminated film, LiF / SiO ２ / Al ２ O ３ laminated film, SiO ２ / TiO ２ laminated film, SiO ２ / Ta ２ O ５ laminated film, SiO ２ / ZrO ２ laminated film, Al ２ O ３ / TiO ２ laminated film, Al ２ O ３ / Ta ２ O ５ laminated film, Al ２ O ３ / ZrO ２ The photoelectric conversion element according to claim 9, characterized in that it is composed of any one of the laminated films.

11. The n-side second region is Al ２ O ３ film, SiO ２ film, LiF film, LiF / SiO ２ laminated film, LiF / Al ２ O ３ laminated film, SiO ２ / Al ２ O ３ laminated film, LiF / SiO ２ / Al ２ O ３ laminated film, SiO ２ / TiO ２ laminated film, SiO ２ / Ta ２ O ５ laminated film, SiO ２ / ZrO ２ laminated film, Al ２ O ３ / TiO ２ laminated film, Al ２ O ３ / Ta ２ O ５ laminated film, Al ２ O ３ / ZrO ２ laminated film, and any one of ITO, ZnO, SnO ２ , In ２ O ３ , AZO, and a transparent conductive film formed by laminating any one of them, and the photoelectric conversion element according to claim 10, characterized in that it is formed by laminating them.

12. having a photoelectric conversion body in which an n-type semiconductor layer, a multiple quantum well layer, and a p-type semiconductor layer are laminated in this order, external light is incident on the photoelectric conversion body from the p-type semiconductor layer side, the n-type semiconductor layer and the p-type semiconductor layer contain gallium nitride, the multiple quantum well layer is formed by laminating one or more pairs of a quantum well layer containing indium gallium nitride and a barrier layer containing gallium nitride, a reflective layer is formed on the n-type semiconductor layer, and the photoelectric conversion element is characterized by this.

13. The reflective layer is composed of any one of an Ag film, an Ag / Cu laminated film, a Mg film, an ITO / Ag laminated film, an Ag / La laminated film, a Cu-doped In ２ O ３ film, and a Ni / Au / W / Ag laminated film. The photoelectric conversion element according to claim 12, characterized by this.

14. The reflective layer is a dielectric, TiO ２ / SiO ２ laminated film, TiO ２ / Al ２ O ３ laminated film, ZrO ２ / SiO ２ laminated film, ZrO ２ / Al ２ O ３ laminated film, Ta ２ O ５ / SiO ２ laminated film, Ta ２ O ５ / Al ２ O ３ The photoelectric conversion element according to claim 12, characterized in that it is composed of any one of the laminated films.

15. the reflective layer is an n-side electrode layer, the n-side electrode layer has an n-side first region and an n-side second region, the n-side first region is composed of any one of a Ti / Al laminated film, a Ti / Al / Ni / Au laminated film, a Ti / Al / Ti / Au laminated film, and a Ti / Al / Ti / Pt / Au laminated film. The n-side second region is TiO ２ / SiO ２ laminated film, TiO ２ / Al ２ O ３ laminated film, ZrO ２ / SiO ２ laminated film, ZrO ２ / Al ２ O ３ laminated film, Ta ２ O ５ / SiO ２ laminated film, Ta ２ O ５ / Al ２ O ３ laminated film, and is characterized in that it is composed of any one of the laminated films. The photoelectric conversion element according to claim 12.

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