JP2011222620A - Solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar cell, made from a compound semiconductor layer hetero-epitaxially grown on a substrate though, which permits a carrier generated by absorbing sunlight spectrum to be extracted efficiently without causing it to recombine in a dislocation-related trap.SOLUTION: The solar cell of the present invention comprises a substrate 102 having a principal plane and a first conductivity-type InGaP(0<x≤1) formed on the substrate 102, a light absorbing layer 103 having a plurality of regions with mutually different In composition ratios and a second conductivity-type InGaP(0<y≤1), different from the first conductivity type, which is formed on the light absorbing layer 103, and a light absorbing layer 104 having a plurality of regions with mutually different In composition ratios, wherein the respective plural regions of the light absorbing layer 103 and the respective plural regions of the light absorbing layer 104 are distributed in the form of quantum dots in-plane parallel to the principal plane.

Description

  The present invention relates to a solar cell. In particular, the present invention relates to a solar cell including a III-V compound semiconductor.

  In manufacturing a solar cell crystal using a group III-V compound semiconductor as a light absorption layer, in order to prevent the occurrence of dislocation due to lattice mismatch, a lattice constant of a substrate to be used and a layer to be epitaxially grown thereon are formed. It is common to match the lattice constant of the crystal. For this reason, a GaAs substrate or a Ge substrate having a lattice constant close to that of GaAs is used. However, considering the cost of the solar battery cell, it is important to reduce the cost of the substrate to be used. Since GaAs substrates and Ge substrates are expensive, the epitaxial growth of compound semiconductors such as GaAs on inexpensive Si substrates widely used in electronic devices, so-called heteroepitaxy on Si substrates, has also been studied.

Japanese Patent Laid-Open No. 61-091098 Japanese Unexamined Patent Publication No. 7-2221030

Applied Physics Letters, 56, p. 2225, 1990. Journal of Applied Physics, 58, p. 3601, 1985. Applied Physics Letters, 53, p. 2293, 1988.

However, the lattice constant of GaAs is 0.5653 nm, whereas the lattice constant of Si is 0.5431 nm, resulting in a lattice mismatch of about 4%. Therefore, crystal growth of GaAs on a Si substrate is generally very difficult. If no countermeasure is taken, dislocations of the order of 10 ⁸ cm ⁻³ will occur. Such dislocation is considered to occur due to the difference in thermal expansion coefficient between Si and GaAs when the growth temperature is lowered to room temperature (for example, Non-Patent Document 1). .

  Such dislocations cause carriers generated in the semiconductor layer by absorbing sunlight to be recombined before being taken out of the cell from the electrode. Therefore, even if a semiconductor material that efficiently absorbs sunlight is selected, the energy that can be extracted to the outside decreases, leading to a decrease in conversion efficiency (for example, Non-Patent Document 2).

Thus, in order to reduce the density of such dislocations, methods such as a superlattice buffer layer and thermal cycle annealing have been proposed (for example, Patent Document 1 and Non-Patent Document 3), which are actually applied to the manufacture of solar cells. As a result, the dislocation density can be reduced to about 10 ⁶ cm ⁻³ . However, even when Si is grown on a GaAs substrate, the level of dislocation density is higher by one digit or more. In addition, a method for reducing the dislocation density by devising a buffer layer or the like has been tried (for example, Patent Document 2). However, even if such a method is applied to a solar cell, the conversion efficiency is sufficiently increased. However, solar cells on a substrate made of Si or the like have not been put into practical use yet.

  Accordingly, an object of the present invention is to trap carriers generated by absorbing the solar spectrum, which are produced by growing a layer made of a compound semiconductor on a substrate by heteroepitaxy. It is an object of the present invention to provide a solar cell having a structure that can be efficiently taken out without recombination.

In order to achieve the above object, the present invention comprises a substrate having a principal surface and a first conductivity type In _x Ga _1-x P (0 <x ≦ 1) formed on the substrate. Is formed on the first light absorption layer and has a second conductivity type different from the first conductivity type. In _y Ga _1-y P (0 <Y ≦ 1), and a second light absorption layer having a plurality of regions having different In composition ratios, each of the plurality of regions of the first light absorption layer, and the second light absorption layer Provided is a solar cell in which each of the plurality of regions is distributed in the form of quantum dots in a plane parallel to the main surface.

  In the solar cell, the plurality of regions of the first light absorption layer include a first In-rich region having an In composition ratio higher than the average In composition ratio of the first light absorption layer, and the second light absorption. A plurality of regions of the layer include a second In-rich region having an In composition ratio higher than the average In composition ratio of the second light absorption layer, and the position of the first In-rich region in plan view; The position of the rich region in plan view may be substantially matched.

  In the solar cell, the size of the first In-rich region in plan view is smaller than the average distance between dislocations of the first light absorption layer, and the size of the second In-rich region in plan view is You may make it smaller than the average distance of the dislocation of 2 light absorption layers.

  In the solar cell, both the average In composition ratio x of the first light absorption layer and the average In composition ratio y of the second light absorption layer are 0.28 or more in a plane parallel to the main surface. It is preferably 1 or less.

In the solar cell, the third conductivity type In _z Ga _1-z P (0 <z ≦ 0) is formed on the second light absorption layer and is different from the first conductivity type and the second conductivity type. 1), and further comprising a third light absorption layer having a plurality of regions having different In composition ratios, and each of the plurality of regions of the third light absorption layer is in the form of quantum dots within a plane parallel to the main surface. It is preferable that they are distributed.

  In the solar cell, the plurality of regions of the third light absorption layer include a third In rich region having an In composition ratio higher than the average In composition ratio of the third light absorption layer, and the second In rich region. The position of the region in plan view and the position of the third In-rich region in plan view can be substantially matched.

  In the solar cell, the size of the first In-rich region in plan view is smaller than the average distance between dislocations of the first light absorption layer, and the size of the second In-rich region in plan view is It is preferable that the average distance between dislocations of the second light absorption layer is smaller than the average distance between dislocations of the third light absorption layer.

  In the solar cell, the average In composition ratio x of the first light absorption layer, the average In composition ratio y of the second light absorption layer, and the average In composition ratio z of the third light absorption layer are all. In the plane parallel to the main surface, it is preferably 0.28 or more and 1 or less.

  The solar cell may include a pn junction formed of a plurality of semiconductor layers having a band gap smaller than the band gap of the first light absorption layer between the substrate and the first light absorption layer. it can.

  In the solar cell, the substrate is preferably made of one material selected from the group consisting of GaAs, InP, Ge, and Si.

  According to the solar cell of the present invention, even in a solar cell produced by growing a layer made of a compound semiconductor on a substrate by heteroepitaxy, carriers generated by absorbing the solar spectrum are related to dislocations. Thus, a solar cell having a structure that can be efficiently taken out without being recombined with a trap is provided.

It is sectional drawing of the photovoltaic cell which concerns on the 1st Embodiment of this invention. It is an energy band figure in the direction parallel to the main surface of the board | substrate of the light absorption layer of the photovoltaic cell which concerns on the 1st Embodiment of this invention. It is sectional drawing of the photovoltaic cell concerning the 2nd Embodiment of this invention. It is sectional drawing of the photovoltaic cell which concerns on the 3rd Embodiment of this invention. It is sectional drawing of the photovoltaic cell which concerns on the modification of the 3rd Embodiment of this invention. (A) is sectional drawing of the photovoltaic cell which concerns on Example 1 of this invention, (b) is an expanded sectional view of the light absorption layer 403 of the photovoltaic cell which concerns on Example 1. FIG. (C) is an enlarged cross-sectional view of the light absorption layer 404 of the solar battery cell according to Example 1. (A) is sectional drawing of the photovoltaic cell which concerns on Example 2 of this invention, (b) is an expanded sectional view of the light absorption layer 503 of the photovoltaic cell which concerns on Example 2. FIG. Further, (c) is an enlarged cross-sectional view of the light absorption layer 504 of the solar battery cell according to Example 2, and (d) is an enlarged cross-sectional view of the light absorption layer 505 of the solar battery cell according to Example 2. It is sectional drawing of the photovoltaic cell which concerns on Example 3 of this invention. It is sectional drawing of the photovoltaic cell which concerns on the modification of Example 1 of this invention. It is sectional drawing of the photovoltaic cell which concerns on the other modification of Example 1 of this invention. It is sectional drawing of the photovoltaic cell which concerns on Example 4 of this invention. It is sectional drawing of the photovoltaic cell which concerns on Example 5 of this invention.

[Summary of embodiment]
In a solar cell in which a light absorption layer is formed of a III-V group compound semiconductor, a substrate having a main surface and an In _x Ga _1-x P (0 <x ≦ 1) of the first conductivity type formed on the substrate. 1), a first light absorption layer having a plurality of regions having different In composition ratios, and a second conductivity type formed on the first light absorption layer and having a second conductivity type different from the first conductivity type. A plurality of regions of the first light absorption layer, each of which includes a plurality of regions made of In _y Ga _1-y P (0 <y ≦ 1) and having different In composition ratios. And the plurality of regions of the second light absorption layer are distributed in a quantum dot shape in a plane parallel to the main surface.

[First Embodiment]
FIG. 1A shows an outline of a cross section of a solar battery cell according to the first embodiment of the present invention.

A solar battery cell 1 as a solar battery according to the first embodiment is formed on a substrate 102 having a main surface and a substrate 102 (that is, on the main surface), and has a first conductivity type In _x Ga _1. A light absorption layer 103 as a first light absorption layer made of _-xP (0 <x ≦ 1) and a second conductivity type different from the first conductivity type, formed on and in contact with the light absorption layer 103; A light absorption layer 104 as a second light absorption layer made of In _y Ga _1-y P (0 <y ≦ 1), an electrode 101 formed on the surface opposite to the main surface of the substrate 102, and light absorption An electrode 105 formed on the layer 104.

  Here, the light absorption layer 103 has a plurality of regions having different In composition ratios. Similarly, the light absorption layer 104 has a plurality of regions having different In composition ratios. Further, in this embodiment, each of the plurality of regions having different In composition ratios in the light absorption layer 103 and each of the plurality of regions having different In composition ratios in the light absorption layer 104 are parallel to the main surface. It is distributed in the form of quantum dots in a simple plane. That is, the plurality of regions have a diameter of several tens to several hundreds of nanometers in plan view and are distributed at intervals in each of the light absorption layers.

  The plurality of regions having different In composition ratios of the light absorption layer 103 include an In rich region 106a as a first In rich region having an In composition ratio higher than the average In composition ratio of the light absorption layer 103, and the average In And a region 106b having an In composition ratio lower than the composition ratio. In a plan view (that is, when observed in a plane parallel to the main surface of the substrate 102), the In rich regions 106a are distributed in the form of quantum dots in the region 106b having a low In composition ratio. Similarly, the plurality of regions having different In composition ratios of the light absorption layer 104 include an In rich region 107a as a second In rich region having an In composition ratio higher than the average In composition ratio of the light absorption layer 104, and the average And a region 107b having an In composition ratio lower than the In composition ratio. In plan view, the In rich regions 107a are distributed in the form of quantum dots in the region 107b having a low In composition ratio. Furthermore, in this embodiment, the light absorption layer 103 is formed so that the position of the In rich region 106a in plan view and the position of the light absorption layer 104 in plan view of the In rich region 107a are substantially matched. Has been.

  Further, the size of the In-rich region 106a of the light absorption layer 103 in plan view is smaller than the average dislocation distance of the light absorption layer 103, and the size of the In-rich region 107a of the light absorption layer 104 in plan view is light absorption. The average distance between dislocations in the layer 104 is preferably smaller. Both the average In composition ratio x of the light absorption layer 103 and the average In composition ratio y of the light absorption layer 104 are preferably 0.28 or more and 1 or less in a plane parallel to the main surface of the substrate 102. .

  FIG. 1B shows an outline of an energy band diagram in a direction parallel to the main surface of the substrate of the light absorption layer of the solar battery cell according to the first embodiment of the present invention.

  As shown in the energy band diagram 108, since the In composition ratio of the In-rich region 106a is higher than the In composition ratio of the region 106b, the band gap of the In-rich region 106a is smaller than the band gap of the region 106b. Therefore, for electrons and holes, the presence in the In-rich region 106a having a small band gap is more stable in terms of energy, and the carriers present in the region 106b easily gather toward the In-rich region 106a.

  Similarly, in the light absorption layer 104, since the band gap of the In-rich region 107a is smaller than the band gap of the region 107b, it is more energetic for electrons and holes to exist in the In-rich region 107a having a smaller band gap. The carriers existing in the region 107b easily gather toward the In-rich region 107a.

  That is, by changing the In composition ratio of the light absorption layer 103 and the light absorption layer 104 along a direction parallel to the main surface of the substrate 102, electrons and holes are collected in the In rich region 106a and the In rich region 107a. Easy functions can be demonstrated. In addition, the position of the light-absorbing layer 103 in the planar view of the In-rich region 106a and the position of the light-absorbing layer 104 in the planar view of the In-rich region 107a substantially coincide with each other, and thus are perpendicular to the main surface of the substrate 102. The In-rich region (that is, the In-rich region 106a and the In-rich region 107a) can be made continuous (that is, can be made continuous continuously) in any direction. Accordingly, the In rich region 106a and the In rich region 107a can reach the electrode 105 while collecting electrons and holes.

  Note that InP-based semiconductor lasers widely used for optical communication and the like have properties that are less likely to deteriorate than GaAs-based semiconductor lasers widely used for optical disk pickup. This is considered to be caused by the amount of In contained in the crystals constituting them. That is, crystals having a high In composition ratio used for InP semiconductor lasers are unlikely to deteriorate because dislocation growth is suppressed.

  In addition, the solar cell 1 according to the present embodiment absorbs light by the light absorption layer 103 and the light absorption layer 104, and carriers generated by the light absorption layer 103 and the light absorption layer 104 are converted into In rich regions 106a and In The electrode 105 is reached while being collected in the rich region 107a. Since the In-rich region 106a and the In-rich region 107a have a high In composition ratio, the growth of dislocations and the like are suppressed, and the In-rich region 107a is hardly deteriorated. Therefore, in such a solar battery cell 1, the excess recombination of carriers due to dislocation can be suppressed, and thereby the conversion efficiency of the solar battery cell 1 can be increased.

  On the other hand, an example of a semiconductor element that has been put into practical use despite the large number of dislocations is an InGaN-based blue semiconductor laser formed on a sapphire substrate. The reason that this semiconductor laser can oscillate is also due to the high In composition ratio. In other words, the In composition ratio of InGaN fluctuates in the plane, carriers are localized in the In rich region where the In composition ratio is high, and excitons (excitons) in which electrons and holes are weakly bonded are formed to form quantum dots. This is thought to be because it is difficult to be affected by dislocations because it functions as described above and its size is smaller than the average interval of dislocation density.

  That is, if the size of the In-rich region 106a and the In-rich region 107a in the light absorption layer 103 and the light absorption layer 104 is smaller than the average dislocation density of the crystals of the light absorption layer 103 and the light absorption layer 104, Carriers are localized in the In-rich region 106a and the In-rich region 107a. Thereby, the recombination of the carrier by a dislocation can be suppressed significantly. Therefore, if the size of the In-rich region 106a and the In-rich region 107a of the light absorption layer 103 and the light absorption layer 104 is made smaller than the average interval of the dislocation density of the crystal as in this embodiment, the light absorption layer 103 The generated carriers can be taken out to the electrode without being lost by recombination due to dislocation.

  In addition, in order to efficiently absorb light in the solar battery cell, it is desirable that the light absorption layer 103 and the light absorption layer 104 be formed directly from a transition semiconductor. In the case of InGaP, when the In composition ratio is smaller than 0.28, an indirect transition semiconductor is formed, and the light absorption efficiency is lowered. Therefore, in this embodiment, the In composition ratio of the light absorption layer 103 and the light absorption layer 104 is set in a range of 0.28 to 1.

(Effects of the first embodiment)
In the solar cell 1 according to the first embodiment, the light absorption layer 103 and the light absorption layer 104 absorb light, and carriers generated in the light absorption layer 103 and the light absorption layer 104 have a high In composition ratio. Since it can take out from an electrode through the In rich area | region 106a and the In rich area | region 107a, the recombination of the carrier in the dislocation which exists in the photovoltaic cell 1 can be suppressed. Thereby, even when the crystal | crystallization with a large dislocation density is used for the photovoltaic cell 1, the photovoltaic cell 1 with high conversion efficiency is realizable.

[Second Embodiment]
FIG. 2: shows the outline | summary of the cross section of the photovoltaic cell which concerns on the 2nd Embodiment of this invention.

  The solar cell 2 according to the second embodiment is the solar cell according to the first embodiment, except that the light absorption layer 200 as a third light absorption layer is further provided on the light absorption layer 104. 1 has substantially the same configuration and function. Therefore, detailed description is omitted except for the differences.

The solar battery cell 2 is formed on the substrate 102, the light absorption layer 103 formed on the substrate 102, the light absorption layer 104 formed on the light absorption layer 103, and the light absorption layer 104. The light absorption layer 200 is composed of In _z Ga _1-z P (0 <z ≦ 1) having a third conductivity type different from the second conductivity type and having a plurality of regions having different In composition ratios. And an electrode 101 formed on the surface opposite to the main surface of the substrate 102, and an electrode 105 formed on the light absorption layer 200.

  Here, each of the plurality of regions having different In composition ratios in the light absorption layer 200 is distributed in the form of quantum dots in a plane parallel to the main surface. That is, in the light absorption layer 200, the plurality of regions have a diameter of several tens to several hundreds of nanometers in plan view and are distributed at intervals. The plurality of regions having different In composition ratios of the light absorption layer 200 include an In rich region 201a as a third In rich region having an In composition ratio higher than the average In composition ratio of the light absorption layer 200, and the average In And a region 201b having an In composition ratio lower than the composition ratio. Note that the size of the In-rich region 201 a of the light absorption layer 200 in plan view is preferably smaller than the average dislocation interval of the light absorption layer 200.

  In a plan view (that is, when observed in a plane parallel to the main surface of the substrate 102), the In rich regions 201a are distributed in the form of quantum dots in the region 201b having a low In composition ratio. Further, in the present embodiment, the light absorption layer 104 is formed so that the position of the In rich region 107a in plan view and the position of the light absorption layer 200 in plan view of the In rich region 201a are substantially matched. Has been. That is, in the second embodiment, the position of the light-absorbing layer 103 in the planar view of the In-rich region 106a, the position of the light-absorbing layer 104 in the planar view of the In-rich region 107a, and the In-rich region of the light-absorbing layer 200. The arrangement is such that the position of the region 201a in plan view substantially matches.

  By using the solar battery cell 2 according to the second embodiment, light is absorbed by the light absorption layer 103 to the light absorption layer 200 in the same manner as the solar battery cell 1 according to the first embodiment. When the carriers generated in these light absorption layers are taken out from the electrode 105, recombination of carriers due to dislocations in the solar battery cell 2 can be suppressed. Thereby, the conversion efficiency of the photovoltaic cell 2 can be improved. Further, for the purpose of improving the light absorption efficiency of the light absorption layer 103 to the light absorption layer 200 by using InGaP as a direct transition semiconductor, the light absorption layer 103, the light absorption layer 104, and the light absorption layer 200 are formed. The In composition ratio is preferably in the range of 0.28 or more and 1 or less.

[Third Embodiment]
FIG. 3A shows an outline of a cross section of a solar battery cell according to the third embodiment of the present invention.

  The solar cell 3 according to the third embodiment is the same as the solar cell 1 according to the first embodiment, except that the solar cell structure 30 is provided between the substrate 102 and the light absorption layer 103. The solar cell 1 according to the first embodiment has substantially the same configuration and function. Therefore, detailed description is omitted except for the differences.

  The solar cell structure 30 is provided on the substrate 102. The solar cell structure 30 includes a pn junction interface 311 composed of a plurality of semiconductor layers having a band gap smaller than that of the semiconductor constituting the light absorption layer 103. Specifically, the plurality of semiconductor layers include a semiconductor layer 300 provided over the substrate 102 and a semiconductor layer 310 provided over the semiconductor layer 300.

  By changing the conductivity type of the semiconductor layer 300 and the conductivity type of the semiconductor layer 310, a pn junction interface 311 exists between the semiconductor layer 300 and the semiconductor layer 310. Therefore, each of the semiconductor layer 300 and the semiconductor layer 310 constitutes a solar cell structure 30 that functions as a light absorption layer, and the entire solar cell 3 constitutes a so-called tandem solar cell.

  Light having energy smaller than the band gap of the light absorption layer 103 reaches the solar cell structure 30 as it is without being absorbed by the light absorption layer 103. Since the band gap of the semiconductor layer 300 and the band gap of the semiconductor layer 310 constituting the solar cell structure 30 are smaller than the band gap of the light absorption layer 103, the light that is not completely absorbed by the light absorption layer 103 is the solar cell structure. 30 and the efficiency of the solar cell can be increased.

  Even in the case of such a tandem solar cell, since the light absorption layer 103 and the light absorption layer 104 have the same functions as those of the first embodiment, the solar cell 1 according to the first embodiment. The same effect can be obtained.

[Modification of Third Embodiment]
FIG. 3B shows an outline of a cross section of a solar battery cell according to a modification of the third embodiment of the present invention.

  The solar battery cell 3a according to the modification of the third embodiment is provided with a solar battery structure 30 between the substrate 102 and the light absorption layer 103 in the solar battery cell 2 according to the second embodiment. Except for the configuration and function substantially the same as those of the solar battery cell 2 according to the second embodiment. And the solar cell structure 30 is equipped with the structure same as the photovoltaic cell 3 which concerns on 3rd Embodiment. Therefore, detailed description is omitted except for the differences.

  Also in the solar battery cell 3a according to the modification of the third embodiment, the light absorption layer 103 to the light absorption layer 200 have the same functions as those of the solar battery cell 2 according to the second embodiment. The effect similar to the photovoltaic cell 2 which concerns on this embodiment is acquired.

  Note that as the substrate 102, a semiconductor substrate formed of one material selected from the group consisting of GaAs, InP, Ge, and Si can be used.

  (A) of FIG. 4 shows the outline | summary of the cross section of the photovoltaic cell which concerns on Example 1 of this invention.

  The solar battery cell 4 according to Example 1 includes a light absorption layer 403 made of n-type doped InGaP with a thickness of 250 nm and a light made of p-type doped InGaP with a thickness of 250 nm on an n-type Si substrate 402. It has a structure in which an absorption layer 404 is laminated in this order, has an n-type electrode 401 on the lower surface of an n-type Si substrate 402, and a p-type transparent electrode on the upper surface of a light absorption layer 404 made of p-type doped InGaP. 405.

  FIG. 4B shows an outline of an enlarged cross section of the light absorption layer 403 of the solar battery cell according to Example 1 of the present invention.

The light absorption layer 403 made of n-type doped InGaP includes 50 pairs of n-type doped InP quantum dots 406c and an n-type doped In _0.49 Ga _0.51 P intermediate layer 406d. , Laminated and manufactured. At this time, the n-type doped InP quantum dots 406 c were formed to be aligned in the vertical direction with respect to the substrate 402 by the self-organization mechanism of the quantum dots. That is, the structure in which the n-type doped InP quantum dots 406c are arranged perpendicular to the substrate surface functions as an In-rich region 406a having an In composition ratio higher than the average In composition ratio of the n-type doped InGaP light absorption layer 403. . Also, the structure in which the n-type doped In _0.49 Ga _0.51 P intermediate layer 406 d is arranged perpendicular to the substrate surface has an In composition lower than the average In composition ratio of the n-type doped InGaP light absorption layer 403. It functions as a region 406b. Note that each of the In-rich region 406a and the region 406b is a direct transition semiconductor because the In composition ratio is in the range of 0.28 to 1.

  (C) of FIG. 4 shows the outline of the expanded cross section of the light absorption layer 404 of the photovoltaic cell which concerns on Example 1 of this invention.

The p-type doped InGaP light absorption layer 404 includes a p-type doped InP quantum dot 407c and a p-type doped In _0.49 Ga _0.51 P intermediate layer 407d as a set, and 50 sets thereof. Laminated and manufactured. At this time, the p-type doped InP quantum dots 407c were formed in the vertical direction with respect to the substrate 402 by the self-organization mechanism of the quantum dots. That is, the structure in which the p-type doped InP quantum dots 407 c are arranged perpendicular to the substrate surface functions as an In-rich region 407 a having an In composition higher than the average In composition ratio of the p-type doped InGaP light absorption layer 404. Further, the structure in which the p-type doped In _0.49 Ga _0.51 P intermediate layer 407 d is arranged perpendicular to the substrate surface has an In composition ratio lower than the average In composition ratio of the p-type doped InGaP light absorption layer 404. Functions as a region 407b. Note that each of the In-rich region 407a and the region 407b is a direct transition semiconductor because the In composition ratio is in the range of 0.28 to 1.

Specifically, the solar battery cell 4 according to Example 1 was manufactured as follows. First, an n-type Si substrate 402 was placed in a MOVPE furnace. Then, in order to remove the oxide on the surface of the n-type Si substrate 402, the inside of the MOVPE furnace was set to 1000 ° C. in a hydrogen atmosphere, and the n-type Si substrate 402 was subjected to heat treatment for 10 minutes. Thereafter, the temperature in the MOVPE furnace was lowered to 540 ° C., and n-doped InP quantum dots 406c were grown at a growth rate of 0.2 ML / s by an amount corresponding to 4 ML. The raw materials used at this time were trimethylindium, phosphine and disilane. Next, the temperature in the MOVPE furnace was raised to 600 ° C., and a 5 nm n-type doped In _0.49 Ga _0.51 P intermediate layer 406 d was grown at a growth rate of 0.7 μm / h. The raw materials used at this time were trimethylgallium, trimethylindium, phosphine, and disilane.

Thus, a total of 50 layers of the n-type doped InP quantum dots 406c and the n-type doped In _0.49 Ga _0.51 P intermediate layer 406d are stacked, so that a total of 250 nm of the n-type doped light absorption layer is formed. 403 was formed. The carrier concentration of this layer was 5 × 10 ¹⁷ cm ⁻³ .

Subsequently, the temperature in the MOVPE furnace was lowered to 540 ° C., and p-doped InP quantum dots 407c were grown at a growth rate of 0.2 ML / s by an amount corresponding to 4 ML. The raw materials used at this time were trimethylindium, phosphine, and diethylzinc. Further, the temperature in the MOVPE furnace was increased to 600 ° C., and a 5 nm p-type doped In _0.49 Ga _0.51 P intermediate layer 407 d was grown at a growth rate of 0.7 μm / h. The raw materials used at this time were trimethylgallium, trimethylindium, phosphine, and diethylzinc.

Thus, a total of 50 layers of p-type doped InP quantum dots 407c and p-type doped In _0.49 Ga _0.51 P intermediate layer 407d are stacked, so that a total of 250 nm of p-type doped light absorption layer is formed. 404 was formed. The carrier concentration of this layer was 1 × 10 ¹⁸ cm ⁻³ .

  Finally, an n-type electrode 401 made of an alloy made of gold and zinc is formed on the lower surface of the n-type Si substrate 402, and a p-type transparent made of ITO is formed on the upper surface of the p-type light absorption layer 404. An electrode 405 was formed.

  The cross-sectional structure of the solar battery cell 4 of Example 1 produced as described above was confirmed by SEM and TEM. As a result, it was confirmed that both the quantum dots of the light absorption layer 403 and the quantum dots of the light absorption layer 404 were aligned in a direction perpendicular to the surface of the substrate 402. This is considered to be due to self-organization due to strain energy due to the formation of quantum dots. Furthermore, the quantum dots of the light absorption layer 403 and the quantum dots of the light absorption layer 404 arranged in the vertical direction (that is, the normal direction of the main surface of the substrate 402) in the cross section of the solar battery cell 4 are in contact with each other. Was also confirmed.

In addition, on the same conditions as Example 1, only the quantum dot was grown on the board | substrate and the magnitude | size and density were investigated. As a result, the diameter of the quantum dots was 25 nm, and the density was 1 × 10 ¹⁰ cm ⁻² . Moreover, when the dislocation density of the photovoltaic cell 4 was examined separately, it was found to be 1 × 10 ⁸ cm ⁻² . In this case, the size of the In-rich region 406a of the light absorption layer 403 and the In-rich region 407a of the light absorption layer 404 in plan view is 25 nm, which is the same as the quantum dot diameter, and the dislocation density is 1 × 10 ⁸ cm ^−2. It was also found that the average distance between dislocations in the crystal was sufficiently smaller than 1.1 μm. And when conversion efficiency was measured with the reference spectrum of AM1.5 about the photovoltaic cell 4, it was 3.2%.

Further, solar cells having the same structure were prepared in place of the substrate 402 made of n-type GaAs. And when the conversion efficiency was measured with the reference spectrum of AM1.5 about the said photovoltaic cell, it was 3.6%. In other words, the solar battery cell 4 on the substrate made of Si uses a substrate made of GaAs that can substantially ignore the influence of the dislocation even though the dislocation density of the light absorption layer is as high as 1 × 10 ⁸ cm ⁻² . It was confirmed that a conversion efficiency of about 90% of the obtained solar battery cell was obtained. From this, by using the solar battery cell 4 according to Example 1, carriers generated in the light absorption layer 403 and the light absorption layer 404 due to light absorption can be extracted from the electrode via the In-rich region. It was confirmed that the carrier recombination at the dislocation was suppressed and the carrier could be effectively taken out to the outside.

  (A) of FIG. 5 shows the outline | summary of the cross section of the photovoltaic cell which concerns on Example 2 of this invention.

  A solar battery cell 5 according to Example 2 includes an n-type doped InGaP light absorption layer 503 having a thickness of 100 nm, an undoped InGaP light absorption layer 504 having a thickness of 300 nm, and an n-type Si substrate 502. It has a structure in which a p-type doped InGaP light absorption layer 505 having a thickness of 100 nm is stacked in this order. Further, the solar cell 5 includes an n-type electrode 501 provided on the lower surface of the n-type Si substrate 502 (that is, the surface opposite to the main surface), and the upper surface of the p-type doped InGaP light absorption layer 505. And a p-type transparent electrode 506 provided on the substrate.

  (B) of FIG. 5 shows the outline of the expanded cross section of the light absorption layer 503 of the photovoltaic cell according to Example 2 of the present invention.

The n-type doped InGaP light absorption layer 503 includes an n-type doped InP quantum dot 507c and an n-type doped In _0.49 Ga _0.51 P intermediate layer 507d. Laminated and manufactured. At this time, the n-doped InP quantum dots 507 c were formed in the vertical direction with respect to the substrate 502 by the self-organization mechanism of the quantum dots. That is, the structure in which the n-type doped InP quantum dots 507c are arranged perpendicular to the substrate surface functions as an In-rich region 507a having an In composition ratio higher than the average In composition ratio of the n-type doped InGaP light absorption layer 503. . Further, the structure in which the n-type doped In _0.49 Ga _0.51 P intermediate layer 507 d is arranged perpendicular to the substrate surface has an In composition lower than the average In composition ratio of the n-type doped InGaP light absorption layer 503. It functions as the area 507b. Note that both the In-rich region 507a and the region 507b are direct transition semiconductors because the In composition ratio is in the range of 0.28 to 1.

  (C) of FIG. 5 shows the outline of the expanded cross section of the light absorption layer 504 of the photovoltaic cell which concerns on Example 2 of this invention.

The undoped InGaP light absorption layer 504 is manufactured by stacking 60 sets of undoped InP quantum dots 508c and an undoped In _0.49 Ga _0.51 P intermediate layer 508d. . At this time, the undoped InP quantum dots 508c were formed in the vertical direction with respect to the substrate 502 by the self-organization mechanism of the quantum dots. That is, the structure in which the undoped InP quantum dots 508 c are arranged perpendicular to the substrate surface functions as an In rich region 508 a having an In composition ratio higher than the average In composition ratio of the undoped InGaP light absorption layer 504. Further, the structure in which the undoped In _0.49 Ga _0.51 P intermediate layer 508 d is arranged perpendicular to the substrate surface is a region 508 b having an In composition ratio lower than the average In composition ratio of the undoped InGaP light absorption layer 504. Function. Note that both the In-rich region 508a and the region 508b are direct transition semiconductors because the In composition ratio is in the range of 0.28 to 1.

  (D) of FIG. 5 shows the outline of the expanded cross section of the light absorption layer 505 of the photovoltaic cell which concerns on Example 2 of this invention.

The p-type doped InGaP light absorption layer 505 includes a p-type doped InP quantum dot 509c and a p-type doped In _0.49 Ga _0.51 P intermediate layer 509d as one set, and 20 sets thereof. It was manufactured by stacking. At this time, the p-doped InP quantum dots 509c were formed in the vertical direction with respect to the substrate 502 by the self-organization mechanism of the quantum dots. That is, the structure in which the p-doped InP quantum dots 509c are arranged perpendicular to the substrate surface functions as an In-rich region 509a having an In composition ratio higher than the average In composition ratio of the p-doped InGaP light absorption layer 505. . The structure in which the p-type doped In _0.49 Ga _0.51 P intermediate layer 509 d is arranged perpendicularly to the substrate surface has an In composition ratio lower than the average In composition ratio of the p-type doped InGaP light absorption layer 505. Functions as a region 509b. Note that both the In-rich region 509a and the region 509b are direct transition semiconductors because the In composition ratio is in the range of 0.28 to 1.

Specifically, the solar battery cell 5 according to Example 2 was manufactured as follows. First, an n-type Si substrate 502 was placed in a MOVPE furnace. Then, in order to remove the oxide on the surface of the n-type Si substrate 502, the inside of the MOVPE furnace was set to 1000 ° C. in a hydrogen atmosphere, and the n-type Si substrate 502 was subjected to heat treatment for 10 minutes. Thereafter, the temperature in the MOVPE furnace was lowered to 540 ° C., and n-doped InP quantum dots 507c were grown at a growth rate of 0.2 ML / s by an amount corresponding to 4 ML. The raw materials used at this time were trimethylindium, phosphine, and disilane. Next, the temperature in the MOVPE furnace was raised to 600 ° C., and a 5 nm n-type doped In _0.49 Ga _0.51 P intermediate layer 507 d was grown at a growth rate of 0.7 μm / h. The raw materials used at this time were trimethylgallium, trimethylindium, phosphine, and disilane.

Thus, a total of 20 layers of the n-type doped InP quantum dots 507c and the n-type doped In _0.49 Ga _0.51 P intermediate layer 507d are stacked, so that a total of 100 nm of the n-type doped light absorption layer is formed. 503 was formed. The carrier concentration of this layer was 5 × 10 ¹⁷ cm ⁻³ .

Subsequently, the temperature in the MOVPE furnace was lowered to 540 ° C., and undoped InP quantum dots 508c were grown at a growth rate of 0.2 ML / s by an amount corresponding to 4 ML. Further, the temperature in the MOVPE furnace was raised to 600 ° C., and an undoped In _0.49 Ga _0.51 P intermediate layer 508d having a thickness of 5 nm was grown at a growth rate of 0.7 μm / h. The raw materials used at this time are trimethylindium and phosphine.

In this way, a total of 60 layers of undoped InP quantum dots 508c and undoped In _0.49 Ga _0.51 P intermediate layer 508d were stacked to form an undoped light absorption layer 504 having a total of 300 nm. The raw materials used at this time were trimethylgallium, trimethylindium, and phosphine.

Subsequently, the temperature in the MOVPE furnace was lowered to 540 ° C., and p-doped InP quantum dots 509c were grown at a growth rate of 0.2 ML / s by an amount corresponding to 4 ML. The raw materials used at this time were trimethylindium, phosphine, and diethylzinc. Further, the temperature in the MOVPE furnace was increased to 600 ° C., and a 5 nm thick p-type doped In _0.49 Ga _0.51 P intermediate layer 509 d was grown at a growth rate of 0.7 μm / h. The raw materials used at this time were trimethylgallium, trimethylindium, phosphine, and diethylzinc.

In this way, a total of 20 layers of p-type doped InP quantum dots 509c and p-type doped In _0.49 Ga _0.51 P intermediate layer 509d are stacked, so that a total of 100 nm of p-type doped light absorption layer is obtained. 505 was formed. The carrier concentration of this layer was 1 × 10 ¹⁸ cm ⁻³ .

  Finally, an n-type electrode 501 made of an alloy made of gold and zinc is formed on the lower surface of the n-type Si substrate 502, and a p-type transparent made of ITO is formed on the upper surface of the p-type light absorption layer 505. An electrode 506 was formed.

  The cross-sectional structure of the solar battery cell 5 of Example 2 produced as described above was confirmed by SEM and TEM. As a result, it was confirmed that all the quantum dots of the light absorption layer 503 to the light absorption layer 505 were aligned in a direction perpendicular to the surface of the substrate 502. This is considered to be due to self-organization due to strain energy due to the formation of quantum dots. Furthermore, the quantum dots of the light absorption layer 503 and the quantum dots of the light absorption layer 504 arranged in the vertical direction in the cross section of the solar battery cell 5 are in contact with each other, and the quantum dots of the light absorption layer 504 and the quantum dots of the light absorption layer 505 It was also confirmed that were in contact with each other.

In addition, on the same conditions as Example 2, only the quantum dot was grown on the board | substrate and the magnitude | size and density were investigated. As a result, the diameter of the quantum dots was 25 nm, and the density was 1 × 10 ¹⁰ cm ⁻² . Moreover, when the dislocation density of the photovoltaic cell 5 was examined separately, it was found to be 1 × 10 ⁸ cm ⁻² . In this case, the size of the In-rich region of each light absorption layer is 25 nm, which is the same as the diameter of the quantum dots, and is sufficiently smaller than an average dislocation distance of 1.1 μm in a crystal having a dislocation density of 1 × 10 ⁸ cm ⁻² . I also understood that. And when the conversion efficiency was measured with the reference spectrum of AM1.5 about the photovoltaic cell 5, it was 3.4%.

Also, solar cells having the same structure were prepared in place of the substrate 502 made of an n-type GaAs substrate. And when the conversion efficiency was measured with the reference spectrum of AM1.5 about the said photovoltaic cell, it was 4.2%. That is, the solar cell 5 on the substrate made of Si has a dislocation density of 1 × 10 ⁸ cm ^{−2 in} the light absorption layer, and the solar cell on the GaAs substrate can substantially ignore the influence of the dislocation. It was confirmed that about 80% of the conversion efficiency was obtained. From this, by using the solar battery cell 5 according to Example 2, the carriers generated in the light absorption layer 503 to the light absorption layer 505 due to light absorption are extracted from the electrode via the In-rich region, thereby dislocation. It was confirmed that the recombination of carriers in the substrate was suppressed and the carriers could be effectively taken out to the outside.

  FIG. 6: shows the outline | summary of the cross section of the photovoltaic cell which concerns on Example 3 of this invention.

  The solar battery cell 6 according to Example 3 includes a light absorption layer 611 made of n-type doped Si, an intermediate contact layer 613 made of n-type doped GaAs, and an n-type doped layer on a p-type Si substrate 602. The InGaP light absorption layer 603, the undoped InGaP light absorption layer 604, and the p-type InGaP light absorption layer 605 are stacked in this order. Further, the solar cell 6 includes a p-type electrode 601 provided on the lower surface of the p-type Si substrate 602, an n-type intermediate electrode 614 provided on the n-type doped GaAs intermediate contact layer 613, and a p-type. A p-type transparent electrode 606 provided on the doped InGaP light absorption layer 605.

  In the solar cell 6, a boundary surface between the p-type Si substrate 602 and the n-type doped Si light absorption layer 611 is a pn junction interface 612, and the p-type Si substrate 602 also functions as a light absorption layer. Thus, the solar cell structure 610 is constituted by the substrate 602 and the light absorption layer 611. Thereby, in the whole photovoltaic cell 6, the tandem-type photovoltaic cell structure is comprised.

Further, the n-type doped InGaP light absorbing layer 603, the undoped InGaP light absorbing layer 604, and the p-type doped InGaP light absorbing layer 605 are respectively the light absorbing layer 503 of the solar cell 5 according to the second embodiment. The light absorption layer 504 and the light absorption layer 505 have the same configuration and function. That is, the n-type doped InGaP light absorption layer 603 includes an In-rich region 607a having a stacked structure of n-type doped InP quantum dots and an n-type doped In _0.49 Ga _0.51 P intermediate layer. Area 607b.

Here, the band gap energy of InP is 1.35 eV, the band gap energy of In _0.49 Ga _0.51 P is 1.88 eV, and the p-type Si substrate 602 constituting the solar cell structure 610 and n The band gap energy with the light absorption layer 611 of type-doped Si is 1.12 eV. Therefore, the band gap energy of the p-type Si substrate 602 and the band gap energy of the n-type doped Si light absorption layer 611 are smaller than the band gap energy of the light absorption layers 603 to 605.

Specifically, the solar battery cell 6 according to Example 3 was manufactured as follows. First, As atoms were diffused in a p-type Si substrate 602 using a thermal diffusion furnace, an n-type doped Si light absorption layer 611 was formed on the surface of the substrate 602. At this time, the thickness of the n-type doped Si light absorption layer 611 was 0.5 μm, and the carrier concentration was 1 × 10 ¹⁹ cm ⁻³ .

Next, the surface of the p-type Si substrate 602 on which the n-type doped Si light absorption layer 611 was formed was cleaned. Thereafter, the substrate 602 was placed in a MOVPE furnace. Then, in order to remove the oxide on the surface of the substrate 602, the inside of the MOVPE furnace was set to 1000 ° C. in a hydrogen atmosphere, and a heat treatment for 10 minutes was performed on the n-type Si substrate 602. Thereafter, the temperature in the MOVPE furnace was lowered to 700 ° C., and an n-type doped GaAs intermediate contact layer 613 was grown by 50 nm. The raw materials used at this time are trimethylgallium, arsine, and disilane. The carrier concentration of this layer was 5 × 10 ¹⁸ cm ⁻³ . Since the structure above the intermediate contact layer 613 of n-type doped GaAs is the same as that of the second embodiment, detailed description thereof is omitted.

  The cross-sectional structure of the solar battery cell 6 according to Example 3 manufactured as described above was confirmed by SEM and TEM. As a result, it was confirmed that the quantum dots of each light absorption layer were aligned in a direction perpendicular to the surface of the substrate 602. This is considered to be due to self-organization due to strain energy due to the formation of quantum dots. Further, it was confirmed that the quantum dots arranged in the vertical direction in the cross section of the solar battery cell 6 were in contact with each other.

In addition, on the same conditions as Example 3, only the quantum dot was grown on the board | substrate, and the magnitude | size and density were investigated. As a result, the diameter of the quantum dots was 25 nm, and the density was 1 × 10 ¹⁰ cm ⁻² . Moreover, when the dislocation density of the photovoltaic cell 6 was examined separately, it was found to be 1 × 10 ⁸ cm ⁻² . In this case, the size of the In-rich region of each light absorption layer is 25 nm, which is the same as the diameter of the quantum dots, and is sufficiently smaller than the average dislocation distance of 1.1 μm in a crystal having a dislocation density of 1 × 10 ⁸ cm ⁻² . I also understood that. And about the photovoltaic cell 6, when it measured conversion efficiency with the reference spectrum of AM1.5, it was 12%.

The value of this conversion efficiency is greatly contributed by the solar cell structure 610 composed of the p-type Si substrate 602 and the n-type doped Si light absorption layer 611, but the single cell solar having the same structure as the solar cell structure 610. Considering that the conversion efficiency of the battery was 9%, n-type doped InGaP light absorption layer 603, undoped InGaP light absorption layer 604, and p-type doped InGaP light absorption layer It was found that the contribution of the solar cell structure consisting of 605 is about 3%. This value is sufficiently large considering that the dislocation density of the light absorption layer is as high as 1 × 10 ⁸ cm ⁻² .

  FIG. 7A shows an outline of a cross section of a solar battery cell according to a modification of Example 1 of the present invention.

  In the cross-sectional structure of the solar battery cell 4 according to Example 1 (see, for example, FIG. 4), the In rich region 406 a and the In rich region 407 a completely coincide with each other in a plane parallel to the main surface of the substrate 402. That is, the position of the In rich region 406a in a plan view and the position of the In rich region 407a in a plan view completely match. However, as long as there is a portion where the position of the In rich region 406a in the plan view and the position of the In rich region 407a in the plan view substantially coincide with each other in the plan view of the plurality of In rich regions, They do not have to match each other completely. For example, like the solar battery cell 7 according to the modification of the first embodiment, a part of the end portion of the In rich region 706a may be in contact with a part of the end portion of the In rich region 707a.

  FIG. 7B shows an outline of a cross section of a solar battery cell according to another modification of Example 1 of the present invention.

  In the solar battery cell 7a according to another modification of Example 1, the size of the In-rich region 726a in plan view and the size of the In-rich region 727a in plan view are constant in the direction perpendicular to the main surface of the substrate 722. Need not be. That is, as shown in FIG. 7B, the widths in the cross sections of the solar cells 7a of the In-rich regions 726a and 726b of the light absorption layer 723 and the In-rich regions 727a and 727b of the light absorption layer 724 are constant widths, respectively. May not be included.

  FIG. 8: shows the outline | summary of the cross section of the photovoltaic cell which concerns on Example 4 of this invention.

  The solar battery cell 8 according to Example 4 is the same as the solar battery cell 4 according to Example 1, except that a buffer layer 80 is further provided between the substrate 402 and the light absorption layer 403. The structure and function are provided. By providing the buffer layer 80 over the substrate 402, the crystallinity of the light absorption layer 403 and the light absorption layer 404 can be improved when the light absorption layer 403 and the light absorption layer 404 are formed. The buffer layer 80 employs a superlattice structure (that is, a superlattice buffer layer) in which a plurality of layers made of GaAs, InAs, GaP, InP, and mixed crystals thereof, or layers made of these materials are stacked. can do. In Example 4, an InGaAs / GaAs superlattice buffer layer was used as the buffer layer 80.

  FIG. 9: shows the outline | summary of the cross section of the photovoltaic cell which concerns on Example 5 of this invention.

  The solar cell 9 according to Example 5 has the same configuration and function as the solar cell 4 except that the solar cell 4 according to Example 1 further includes a window layer 90 on the light absorption layer 404. Prepare. As the window layer 90, for example, a layer made of AlInP or a layer made of AlGaInP can be used. In Example 5, the window layer 90 was formed from a p-type AlInP layer. By providing the window layer 90, it is possible to suppress a decrease in carriers due to surface recombination. The solar battery cell 9 can further include a buffer layer 80 on the substrate 402 as in the fourth embodiment.

  In addition, although the board | substrate which consists of Si was used for the photovoltaic cell which concerns on Example 1 thru | or 5, the board | substrate which consists of materials (for example, GaAs etc.) different from Si can also be used. Moreover, although each light absorption layer of the photovoltaic cell which concerns on Example 1 thru | or 5 was formed using the self-organization mechanism of a quantum dot, it is produced combining photolithography technology, etching technology, and regrowth technology. You can also. Furthermore, each light absorption layer etc. can also be formed using methods, such as MBE, LPE, or HVPE, instead of MOVPE.

  While the embodiments and examples of the present invention have been described above, the embodiments and examples described above do not limit the invention according to the claims. In addition, it should be noted that not all the combinations of features described in the embodiments and examples are essential to the means for solving the problems of the invention.

1, 2, 3, 3a, 4, 5, 6, 7, 7a, 8, 9 Solar cell 30 Solar cell structure 80 Buffer layer 90 Window layer 101, 105 Electrode 102 Substrate 103, 104 Light absorption layer 106a, 107a In Rich region 106b, 107b region 108 Energy band diagram 200 Light absorption layer 201a In rich region 201b Region 300, 310 Semiconductor layer 311 pn junction interface 401 Electrode 402 Substrate 403, 404 Light absorption layer 405 Transparent electrode 406a, 407a In rich region 406b, 407b region 406c, 407c quantum dot 406d, 407d intermediate layer 501 electrode 502 substrate 503, 504, 505 light absorption layer 506 transparent electrode 507a, 508a, 509a In rich region 507b, 508b, 509b region 507c , 508c, 509c Quantum dot 507d, 508d, 509d Intermediate layer 601, 606 Electrode 602 Substrate 603, 604, 605 Light absorption layer 607a, 608a, 609a In rich region 607b, 608b, 609b region 610 Solar cell structure 611 Light absorption layer 612 pn junction interface 613 Intermediate contact layer 614 Intermediate electrode 703, 704 Light absorption layer 706a, 707a In rich region 706b, 707b region 723, 724 Light absorption layer 726a, 727a In rich region 726b, 726b region

Claims (10)

A substrate having a main surface;
A first light absorption layer formed on the substrate, made of a first conductivity type In _x Ga _1-x P (0 <x ≦ 1), and having a plurality of regions having different In composition ratios;
A plurality of In _y Ga _1-y P (0 <y ≦ 1) having a second conductivity type different from the first conductivity type and formed on the first light absorption layer and having different In composition ratios A second light-absorbing layer having a region of
Each of the plurality of regions of the first light absorption layer and each of the plurality of regions of the second light absorption layer are distributed in a quantum dot shape in a plane parallel to the main surface. Solar cell. The plurality of regions of the first light absorption layer include a first In-rich region having an In composition ratio higher than an average In composition ratio of the first light absorption layer;
The plurality of regions of the second light absorption layer include a second In-rich region having an In composition ratio higher than an average In composition ratio of the second light absorption layer;
2. The solar cell according to claim 1, wherein a position of the first In-rich region in a plan view substantially coincides with a position of the second In-rich region in a plan view. The size of the first In-rich region in plan view is smaller than the average distance between dislocations of the first light absorption layer,
3. The solar cell according to claim 2, wherein a size of the second In-rich region in a plan view is smaller than an average dislocation interval of the second light absorption layer.   Both the average In composition ratio x of the first light absorption layer and the average In composition ratio y of the second light absorption layer are 0.28 or more and 1 or less in a plane parallel to the main surface. The solar cell according to claim 3. Formed of In _z Ga _1-z P (0 <z ≦ 1) of the third conductivity type different from the first conductivity type and the second conductivity type, formed on the second light absorption layer, and In A third light absorption layer having a plurality of regions having different composition ratios;
The solar cell according to claim 2, wherein each of the plurality of regions of the third light absorption layer is distributed in a quantum dot shape in a plane parallel to the main surface. The plurality of regions of the third light absorption layer includes a third In-rich region having an In composition ratio higher than an average In composition ratio of the third light absorption layer;
The solar cell according to claim 5, wherein a position of the second In-rich region in plan view substantially coincides with a position of the third In-rich region in plan view. The size of the first In-rich region in plan view is smaller than the average distance between dislocations of the first light absorption layer,
The size of the second In-rich region in plan view is smaller than the average distance between dislocations in the second light absorption layer,
The solar cell according to claim 6, wherein a size of the third In-rich region in a plan view is smaller than an average dislocation interval of the third light absorption layer.   Each of the average In composition ratio x of the first light absorption layer, the average In composition ratio y of the second light absorption layer, and the average In composition ratio z of the third light absorption layer is the main surface. The solar cell according to claim 7, wherein the solar cell is 0.28 or more and 1 or less in a plane parallel to.   9. The semiconductor device according to claim 1, further comprising a pn junction made of a plurality of semiconductor layers having a band gap smaller than that of the first light absorption layer between the substrate and the first light absorption layer. The solar cell according to item.   The solar cell according to claim 1, wherein the substrate is made of one material selected from the group consisting of GaAs, InP, Ge, and Si.

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