Photoelectric conversion element

Abstract

To improve the thermal conductivity of the photoelectric conversion element.SOLUTION: It is a photoelectric conversion element with a buffer layer grown on an n-type GaAs substrate, a semiconductor multilayer reflector containing AlAs and InGaAs, and an optical absorption layer for absorbing light.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a photoelectric conversion element. [Background technology]

[0002] Light with a wavelength in the 1 micron band is less absorbed by the atmosphere, making it promising for long-distance optical wireless power supply using laser light. However, silicon solar cells, which have traditionally been used for solar power, absorb very little light in this wavelength band. In addition, GaAs, which is known as a highly efficient solar cell, can only convert light with a wavelength shorter than 0.9 microns into electricity due to its band gap. For this reason, InGaAs metamorphic growth (crystal growth with lattice strain relaxation), which is not lattice-matched, is used on a GaAs substrate.

[0003] For example, Non-Patent Document 1 discloses a multi-junction solar cell using a compound (mixed crystal) of InAs and GaAs. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] JFGeisz et al., "40.8% efficient inverted triple-junction solar cell with two independently metamorphic junctions", Applied Physics Letters, Vol. 93, Paper No. 123505, 2008 Summary of the Invention [Problem to be solved by the invention]

[0005] However, conventional photoelectric conversion elements using InAs and GaAs compounds (mixed crystals) have the problem of low thermal conductivity because they impede the movement of phonons, which are quantized lattice vibrations. Therefore, even if there is no problem with sunlight, the temperature of the element rises significantly when it receives high-intensity laser light, increasing the rate of non-radiative recombination of generated electrons and holes, decreasing the internal quantum efficiency, and as a result, there is a possibility that this will result in a significant decrease in photoelectric conversion efficiency.

[0006] The disclosed technique aims to improve the thermal conductivity of a photoelectric conversion element. [Means for solving the problem]

[0007] The disclosed technology includes a buffer layer grown on an n-type GaAs substrate, a semiconductor multilayer reflector including AlAs and InGaAs provided on the buffer layer, and a light absorbing layer for absorbing light provided on the semiconductor multilayer reflector. A photoelectric conversion element, wherein the semiconductor multilayer film reflector has an In composition such that the lattice constants of the AlAs and the InGaAs are compressively and tensilely strained with respect to the GaAs substrate, respectively, and the product of the strain and the film thickness at a high temperature where crystal growth is performed is zero in total. It is a photoelectric conversion element. Effect of the Invention

[0008] According to the disclosed technique, the thermal conductivity of a photoelectric conversion element can be improved. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a partial cross-sectional view of a photoelectric conversion element. [Diagram 2] FIG. 2 is a diagram showing an atomic force microscope image of the surface of an InGaAs buffer layer. [Diagram 3] FIG. 13 is a diagram showing the reflection spectrum of a semiconductor multilayer film reflector in a preliminary experiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention (the present embodiment) will be described with reference to the drawings. The embodiment described below is merely an example, and the embodiment to which the present invention is applied is not limited to the following embodiment.

[0011] (Photoelectric conversion element overview) The photoelectric conversion element according to the present embodiment has a semiconductor multilayer film having high thermal conductivity and optical reflectance, which is formed by alternately growing crystals of AlAs and InGaAs.

[0012] (Layer structure of photoelectric conversion element) The layer structure of the photoelectric conversion element according to this embodiment will be described.

[0013] 1 is a partial cross-sectional view of a photoelectric conversion element. The photoelectric conversion element 10 is formed by forming an n-type InGaAs buffer layer on an n-GaAs substrate 11, which is n-type GaAs. 0.12 Ga 0.88 It has an As buffer 12. 0.12 Ga 0.88 The As buffer 12 is produced, for example, by doping silicon and growing a crystal to a thickness of 1600 nm. 0.12 Ga 0.88 The As buffer 12 has a constant In composition of 0.12.

[0014] Figure 2 shows an atomic force microscope image of the surface of an InGaAs buffer layer. 0.12 Ga 0.88 The As buffer 12 had a low root mean square value of about 1 nm, which is an index of flatness.

[0015] Returning to FIG. 1, the photoelectric conversion element 10 is an n-In 0.12 Ga 0.88 An n-type InGaAs layer, n-In 0.1 Ga 0.9 It has an As layer 13. 0.1 Ga 0.9The As layer 13 is formed, for example, by doping silicon and growing a crystal to a thickness of 300 nm. Although an example in which the In composition is 0.1 (10%) is shown in Fig. 1, the In composition ratio may be changed based on the relationship with the wavelength of the laser light used. Specifically, the In composition may be in the range of 0.05 to 0.30 (5% to 30%).

[0016] Furthermore, the photoelectric conversion element 10 is made of n-In 0.1 Ga 0.9 On the As layer 13, an n-AlAs layer 14 which is an n-type AlAs layer and an n-InGaAs layer 15 which is an n-type InGaAs layer are provided. 0.2 Ga 0.8 The semiconductor multilayer reflector includes about 10 pairs of alternately arranged As layers 15 and As layers 16.

[0017] Each pair of semiconductor multilayer mirrors includes an n-AlAs layer 14 and an n-In 0.2 Ga 0.8 The As layer 15 is formed, for example, by crystal growth so as to have a thickness of λ / 4n, where λ is the resonance wavelength of the laser light used and n is the refractive index.

[0018] The crystal growth method is, for example, metal organic vapor phase epitaxy (MOVPE). 0.09 Al 0.91 As and 90 nm thick In 0.1 Ga 0.9 A semiconductor multilayer mirror was fabricated using As.

[0019] 3 is a diagram showing the reflection spectrum of a semiconductor multilayer reflector in a preliminary experiment. As a result of the preliminary experiment, the fabricated semiconductor multilayer reflector achieved a high reflectance of 90%.

[0020] However, if the InAlAs layer is used as is, there is a problem that the thermal conductivity decreases due to the alloying. Therefore, by using AlAs, which has high thermal conductivity among binary elements, increasing the In composition of InGaAs, and optimizing the crystal growth conditions so that the average lattice distortion is zero, a semiconductor multilayer film that satisfies both high thermal conductivity and high optical reflectance is fabricated.

[0021] Here, the average lattice distortion is defined as (d1×(a1-a3)+d2×(a2-a3)) / (d1+d2), where d1 is the thickness of the AlAs layer, a1 is the lattice constant, d2 is the thickness of the InGaAs layer constituting the reflector, a2 is the lattice constant, and a3 is the lattice constant of the lattice-relaxed InGaAs layer. The thickness of the semiconductor multilayer film reflector is adjusted so that this average lattice distortion is zero. That is, the semiconductor multilayer film reflector has an In composition such that the lattice constants of AlAs and InGaAs are compressive and tensile distortions, respectively, with respect to the n-GaAs substrate 11, and the product of the distortion and the film thickness at high temperatures where crystal growth is performed is zero in total.

[0022] Therefore, the semiconductor multilayer reflector is composed of semiconductor layers with large lattice constants and lattice-relaxed. In this way, by combining AlAs / InGaAs semiconductor multilayer reflectors, it is possible to fabricate a semiconductor multilayer with high thermal conductivity and optical reflectance.

[0023] Returning to FIG. 1, the photoelectric conversion element 10 further includes an n-AlAs layer 14 and an n-In layer 15 stacked alternately. 0.2 Ga 0.8 On the As layer 15, an n-type InGaAs layer, n-In 0.1 Ga 0.9 It has an As light absorbing layer 16. 0.1 Ga 0.9 The As light absorbing layer 16 is formed by, for example, doping silicon and growing the crystal.

[0024] Furthermore, the photoelectric conversion element 10 is made of n-In 0.1 Ga 0.9 On the As light absorption layer 16, a p-type InGaAs layer, p-In 0.1 Ga0.9 It has an As light absorbing layer 17. 0.1 Ga 0.9 The As light absorbing layer 17 is formed by, for example, doping with carbon and growing a crystal.

[0025] p-In 0.1 Ga 0.9 By forming a grid-shaped electrode on the As light absorption layer 17 by photolithography and electrode deposition, a photoelectric conversion element specialized for laser light can be realized. By providing a light absorption layer on a reflector with a high reflectance of 90%, a significant improvement in quantum efficiency is expected compared to conventional technology. In addition, AlAs is a binary compound, and has a high thermal conductivity of 90 W / Km according to literature values, so thermal conductivity can be significantly improved compared to conventional technology.

[0026] In this embodiment, InGaAs is used as the buffer layer, but InAlAs may also be used, because InAlAs also has the effect of reducing lattice distortion in GaAs, similar to InGaAs.

[0027] In this embodiment, the InGaAs buffer layer has an In composition of 0.12, but the In composition ratio may be changed based on the wavelength of the laser light to be used. Specifically, the In composition may be in the range of 0.05 to 0.20 (5% to 20%).

[0028] In this embodiment, In 0.1 Ga 0.9 Since the light absorption layer is made of As, the wavelength of the laser light that can be photoelectrically converted is 0.97 μm or less. The ratio of In composition in the light absorption layer may be changed based on the relationship with the wavelength of the laser light to be used. Specifically, the In composition may be in the range of up to 0.2 (up to 20%). For example, In 0.2 Ga 0.8 If the light absorption layer is made of As, the wavelength of laser light that can be photoelectrically converted can be up to 1.1 μm or less.

[0029] (Summary of the embodiment) This specification describes at least the photoelectric conversion elements described in the following items. (Section 1) a buffer layer grown on an n-type GaAs substrate; a semiconductor multilayer reflector including AlAs and InGaAs; A light absorbing layer for absorbing light. Photoelectric conversion element. (Section 2) The semiconductor multilayer film reflector has an In composition such that the lattice constants of the AlAs and the InGaAs are compressively and tensilely strained with respect to the GaAs substrate, respectively, and the product of the strain and the film thickness at high temperatures for crystal growth is zero in total. 2. The photoelectric conversion element according to item 1. (Section 3) the semiconductor multilayer reflector includes alternating layers of the AlAs and the InGaAs. 3. The photoelectric conversion element according to claim 1 or 2. (Section 4) The semiconductor multilayer film reflector is composed of semiconductor layers having a large lattice constant and being lattice-relaxed. 4. The photoelectric conversion element according to any one of items 1 to 3. (Section 5) The buffer layer is composed of InGaAs or InAlAs having an In composition of 5% to 20% at the surface. 5. The photoelectric conversion element according to any one of items 1 to 4. (Section 6) The light absorbing layer absorbs laser light having a wavelength of 0.7 μm to 1.1 μm. 6. The photoelectric conversion element according to any one of items 1 to 5.

[0030] Although the present embodiment has been described above, the present invention is not limited to such a specific embodiment, and various modifications and variations are possible within the scope of the gist of the present invention described in the claims. [Explanation of symbols]

[0031] 10 Photoelectric conversion element 11 n-GaAs substrate 12 n-In 0.12 Ga 0.88 As Buffer 13 n-In 0.1 Ga 0.9 As layer 14 n-AlAs layer 15 n-In 0.2 Ga 0.8 As layer 16 n-In 0.1 Ga 0.9 As light absorption layer 17 p-In 0.1 Ga 0.9 As light absorption layer

Claims

1. a buffer layer grown on an n-type GaAs substrate; a semiconductor multilayer reflector including AlAs and InGaAs provided on the buffer layer; A photoelectric conversion element comprising: a light absorbing layer for absorbing light, the light absorbing layer being provided on the semiconductor multilayer film reflector; The semiconductor multilayer reflector has an In composition such that the lattice constants of the AlAs and the InGaAs are compressively and tensilely strained with respect to the GaAs substrate, respectively, and the product of the strain and the film thickness at a high temperature for crystal growth is zero in total. Photoelectric conversion element.

2. the semiconductor multilayer reflector includes alternating layers of the AlAs and the InGaAs; The photoelectric conversion element according to claim 1 .

3. The semiconductor multilayer film reflector is composed of semiconductor layers having a large lattice constant and being lattice-relaxed. The photoelectric conversion element according to claim 1 or 2.

4. The buffer layer is made of InGaAs or InAlAs having an In composition of 5% to 20% at the surface. The photoelectric conversion element according to claim 1 .

5. The light absorbing layer absorbs laser light having a wavelength of 0.7 μm to 1.1 μm. The photoelectric conversion element according to claim 1 .

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