A solar cell epitaxial wafer and a method for preparing the same

Abstract

The present invention discloses a solar cell epitaxial wafer and a preparation method thereof. The epitaxial wafer comprises a substrate, a GaN nucleation layer, a GaN intrinsic layer, an N-type GaN layer, an InGaN / GaN superlattice layer, a U-type GaN layer, an InGaN / GaN quantum well layer, and a P-type GaN layer, which are arranged in sequence from bottom to top. The present invention adopts a substrate, a superlattice layer, and an InGaN / GaN quantum well layer structure with a high In component, reduces the dislocation density, improves the light absorption rate, and obtains an epitaxial wafer with high crystal quality. Compared with a solar cell with a traditional epitaxial wafer, a solar cell made of an epitaxial wafer with a high In component has more carrier collection and less surface recombination, thereby improving the photoelectric conversion efficiency of the InGaN / GaN solar cell to a certain extent.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and in particular to a solar cell epitaxial wafer and a preparation method thereof. Background Art

[0002] Among the third-generation semiconductors, the III-V semiconductor GaN is representative. GaN has a wide bandgap of 3.4eV. It has a high melting point of 1700°C and a high ionization degree of about 0.43 to 0.5. In addition, GaN also has high thermal conductivity, breakdown electric field and thermal conductivity. It also has the advantages of strong radiation resistance and high hardness, and has great application value in the fields of optoelectronics and microelectronics.

[0003] Currently, there are many studies on InGaN epiwafers, which mainly focus on the growth process of InGaN multi-quantum wells and subsequent device performance, including the use of lateral epitaxial growth, optimization of the number of multi-quantum well periods, the use of different substrates, growth on different GaN crystal orientations, etc. These methods reveal the relationship between the material quality, structural integrity and corresponding photovoltaic properties of the InGaN layer.

[0004] However, existing solar cells generally have the problem of low photoelectric conversion efficiency. Summary of the invention

[0005] The embodiment of the present invention provides a solar cell epitaxial wafer and a preparation method thereof, which are used to solve the problem of low photoelectric conversion efficiency of solar cells in the prior art.

[0006] In one aspect, an embodiment of the present invention provides a solar cell epitaxial wafer, comprising:

[0007] substrate;

[0008] A GaN nucleation layer is disposed on the top surface of the substrate;

[0009] A GaN intrinsic layer is disposed on the top surface of the GaN nucleation layer;

[0010] An N-type GaN layer is disposed on the top surface of the GaN intrinsic layer;

[0011] An InGaN / GaN superlattice layer is arranged on the top surface of the N-type GaN layer, wherein the InGaN / GaN superlattice layer comprises a plurality of first InGaN layers and first GaN layers, and the first InGaN layers and the first GaN layers are arranged periodically;

[0012] A U-type GaN layer is disposed on the top surface of the InGaN / GaN superlattice layer;

[0013] An InGaN / GaN quantum well layer is arranged on the top surface of the U-type GaN layer, the InGaN / GaN quantum well layer includes a plurality of second InGaN layers and a second GaN layer, the second InGaN layers and the second GaN layers are arranged periodically, wherein the composition of In in the second InGaN layer is 0.30-0.32;

[0014] The P-type GaN layer is arranged on the top surface of the InGaN / GaN quantum well layer.

[0015] On the other hand, an embodiment of the present invention further provides a method for preparing a solar cell epitaxial wafer, comprising:

[0016] preparing a substrate;

[0017] Disposing a GaN nucleation layer on the top surface of the substrate;

[0018] Disposing a GaN intrinsic layer on the top surface of the GaN nucleation layer;

[0019] Disposing an N-type GaN layer on the top surface of the GaN intrinsic layer;

[0020] An InGaN / GaN superlattice layer is disposed on the top surface of the N-type GaN layer, wherein the InGaN / GaN superlattice layer includes a plurality of first InGaN layers and first GaN layers, and the first InGaN layers and the first GaN layers are arranged periodically;

[0021] Disposing a U-type GaN layer on the top surface of the InGaN / GaN superlattice layer;

[0022] An InGaN / GaN quantum well layer is arranged on the top surface of the U-type GaN layer, wherein the InGaN / GaN quantum well layer includes a plurality of second InGaN layers and a second GaN layer, wherein the second InGaN layers and the second GaN layers are arranged periodically, wherein the composition of In in the second InGaN layers is 0.30-0.32;

[0023] A P-type GaN layer is disposed on the top surface of the InGaN / GaN quantum well layer.

[0024] A solar cell epitaxial wafer and a method for preparing the same in the present invention have the following advantages:

[0025] The patterned substrate, superlattice layer and InGaN / GaN quantum well layer structure with high In content are used to reduce dislocation density, improve light absorption rate, and obtain epitaxial wafers with higher crystal quality. Compared with solar cells with traditional epitaxial wafers, solar cells made of epitaxial wafers with high In content have more carrier collection and less surface recombination, which improves the photoelectric conversion efficiency of InGaN / GaN solar cells to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 A schematic structural diagram of a solar cell epitaxial wafer provided by an embodiment of the present invention;

[0028] Figure 2 A PL diagram of a solar cell epitaxial wafer at room temperature provided by an embodiment of the present invention;

[0029] Figure 3 A satellite peak comparison diagram of a solar cell epitaxial wafer and a traditional epitaxial wafer provided by an embodiment of the present invention;

[0030] Figure 4 A comparison diagram of rocking curves of a solar cell epitaxial wafer and a traditional epitaxial wafer provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] Figure 1 A schematic diagram of the structure of a solar cell epitaxial wafer provided by an embodiment of the present invention. An embodiment of the present invention provides a solar cell epitaxial wafer, comprising:

[0033] substrate;

[0034] A GaN nucleation layer is disposed on the top surface of the substrate;

[0035] A GaN intrinsic layer is disposed on the top surface of the GaN nucleation layer;

[0036] An N-type GaN layer is disposed on the top surface of the GaN intrinsic layer;

[0037] An InGaN / GaN superlattice layer is arranged on the top surface of the N-type GaN layer, wherein the InGaN / GaN superlattice layer comprises a plurality of first InGaN layers and first GaN layers, and the first InGaN layers and the first GaN layers are arranged periodically;

[0038] A U-type GaN layer is disposed on the top surface of the InGaN / GaN superlattice layer;

[0039] An InGaN / GaN quantum well layer is arranged on the top surface of the U-type GaN layer, the InGaN / GaN quantum well layer includes a plurality of second InGaN layers and a second GaN layer, the second InGaN layers and the second GaN layers are arranged periodically, wherein the composition of In in the second InGaN layer is 0.30-0.32;

[0040] The P-type GaN layer is arranged on the top surface of the InGaN / GaN quantum well layer.

[0041] Exemplarily, the substrate is a patterned Al 2 O 3 The N-type GaN layer is doped with Si, with a doping concentration of 0.8×10 18 cm -3 -1.2×10 18 cm -3 The period number of the InGaN / GaN superlattice layer is 12, and the In composition in the first InGaN layer is 0.04. The period number of the InGaN / GaN quantum well layer is 12. The P-type GaN layer is doped with Mg, and the doping concentration is 0.8×10 20 cm -3 -1.2×10 20 cm -3 .

[0042] The present invention also provides a method for preparing a solar cell epitaxial wafer, the method comprising:

[0043] S100: Prepare a substrate.

[0044] For example, when preparing the substrate, a MOCVD (Metal-organic Chemical Vapor Deposition) device is used to heat the substrate in a hydrogen atmosphere at 980-1020° C. for 10 minutes.

[0045] S110 , disposing a GaN nucleation layer on the top surface of the substrate.

[0046] Exemplarily, before forming the GaN nucleation layer, the temperature is first lowered to 630-670° C., and then a GaN nucleation layer with a thickness of 77-83 nm is grown on the substrate.

[0047] S120 , disposing a GaN intrinsic layer on the top surface of the GaN nucleation layer.

[0048] Exemplarily, before forming the GaN intrinsic layer, the temperature is first raised to 960-1000° C., and then a GaN intrinsic layer with a thickness of 195-205 nm is grown on the GaN nucleation layer.

[0049] S130 , disposing an N-type GaN layer on the top surface of the GaN intrinsic layer.

[0050] For example, before forming the N-type GaN layer, the temperature is raised to 1050-1090° C., and then a GaN layer with a thickness of 2.4-2.6 μm is grown on the GaN intrinsic layer, and Si is doped into the GaN layer with a doping concentration of 0.8×10 18 cm -3 -1.2×10 18 cm -3 .

[0051] S140 , disposing an InGaN / GaN superlattice layer on the top surface of the N-type GaN layer, wherein the InGaN / GaN superlattice layer includes a plurality of first InGaN layers and first GaN layers, and the first InGaN layers and the first GaN layers are arranged periodically.

[0052] Illustratively, before forming the InGaN / GaN superlattice layer, the temperature is first lowered to 820-860°C, and then an InGaN / GaN superlattice layer with 12 cycles is grown on the N-type GaN layer, wherein the thickness of each first InGaN layer is 2.5nm, the thickness of each first GaN layer is 4nm, and the In composition in the first InGaN layer is 0.04, and the Ga composition is 0.96.

[0053] S150 , disposing a U-type GaN layer on the top surface of the InGaN / GaN superlattice layer.

[0054] For example, before forming the U-type GaN layer, the temperature is raised to 1080-1120° C., and then a U-type GaN layer with a thickness of 77-83 nm is grown. The U-type GaN layer can be used as a buffer layer to adjust the strain between the InGaN / GaN superlattice layer and the InGaN / GaN quantum well layer, while reducing impurity scattering.

[0055] S160. An InGaN / GaN quantum well layer is disposed on the top surface of the U-type GaN layer, wherein the InGaN / GaN quantum well layer includes a plurality of second InGaN layers and a second GaN layer, wherein the second InGaN layers and the second GaN layers are arranged periodically, and wherein the composition of In in the second InGaN layer is 0.30-0.32.

[0056] Exemplarily, in the InGaN / GaN quantum well layer, the thickness of each second InGaN layer is 2.8-3.2 nm, the thickness of each second GaN layer is 8.8-9.2 nm, the composition of In in the second InGaN layer is 0.30-0.32, and the composition of Ga is 0.68-0.70.

[0057] S170 , disposing a P-type GaN layer on the top surface of the InGaN / GaN quantum well layer.

[0058] For example, before forming the P-type GaN layer, the temperature is first lowered to 730-760° C., and then a GaN layer with a thickness of 38-42 nm is grown, and Mg is doped into the GaN layer at a doping concentration of 0.8×10 20 cm -3 -1.2×10 20 cm -3 , that is, the epitaxial wafer is prepared.

[0059] For comparison, the present invention adopts the above method to prepare sample A and sample B. Sample A is prepared completely according to the above process and data, while sample B changes the In component in the InGaN / GaN quantum well layer to 0.25-0.27. Other processes and data are the same as sample A.

[0060] The PL (Photoluminescence) graph, satellite peak graph and rocking curve obtained by analyzing the above sample A and sample B are as follows: Figure 2 , 3 , and 4. The calculation of the PL graph shows that the In component in the InGaN / GaN quantum well layer of sample A is consistent with the In component in the quantum well layer designed above. From the satellite peak graph, it can be seen that sample A has more satellite peaks than sample B, so sample A has better quality. From the rocking curve graph, it can be seen that whether it is the rocking curve of the (002) plane or the (102) plane, sample A is narrower than sample B, has a smaller half-height width, and has better crystal quality.

[0061] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0062] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A solar cell epitaxial wafer, characterized in that: include: substrate; A GaN nucleation layer is disposed on the top surface of the substrate; A GaN intrinsic layer, disposed on the top surface of the GaN nucleation layer; An N-type GaN layer is disposed on the top surface of the GaN intrinsic layer; An InGaN / GaN superlattice layer is disposed on the top surface of the N-type GaN layer, wherein the InGaN / GaN superlattice layer includes a plurality of first InGaN layers and first GaN layers, and the first InGaN layers and the first GaN layers are arranged periodically; A U-type GaN layer is disposed on the top surface of the InGaN / GaN superlattice layer; An InGaN / GaN quantum well layer is disposed on the top surface of the U-type GaN layer, wherein the InGaN / GaN quantum well layer includes a plurality of second InGaN layers and a second GaN layer, wherein the second InGaN layers and the second GaN layers are arranged periodically, wherein the composition of In in the second InGaN layer is 0.32; The P-type GaN layer is arranged on the top surface of the InGaN / GaN quantum well layer.

2. A solar cell epitaxial wafer according to claim 1, characterized in that: The substrate is a patterned Al2O3 substrate.

3. A solar cell epitaxial wafer according to claim 1, characterized in that: The N-type GaN layer is doped with Si, and the doping concentration is 0.8×10 18 cm -3 -1.2×10 18 cm -3 .

4. A solar cell epitaxial wafer according to claim 1, characterized in that: The period number of the InGaN / GaN superlattice layer is 12, wherein the composition of In in the first InGaN layer is 0.

04.

5. The solar cell epitaxial wafer according to claim 1, characterized in that: The period number of the InGaN / GaN quantum well layer is 12.

6. The solar cell epitaxial wafer according to claim 1, characterized in that: The P-type GaN layer is doped with Mg, and the doping concentration is 0.8×10 20 cm -3 -1.2×10 20 cm -3 .

7. A method for preparing a solar cell epitaxial wafer, characterized in that: include: preparing a substrate; Disposing a GaN nucleation layer on the top surface of the substrate; Disposing a GaN intrinsic layer on the top surface of the GaN nucleation layer; Disposing an N-type GaN layer on the top surface of the GaN intrinsic layer; An InGaN / GaN superlattice layer is disposed on the top surface of the N-type GaN layer, wherein the InGaN / GaN superlattice layer includes a plurality of first InGaN layers and first GaN layers, and the first InGaN layers and the first GaN layers are arranged periodically; Disposing a U-type GaN layer on the top surface of the InGaN / GaN superlattice layer; An InGaN / GaN quantum well layer is arranged on the top surface of the U-type GaN layer, wherein the InGaN / GaN quantum well layer includes a plurality of second InGaN layers and a second GaN layer, wherein the second InGaN layers and the second GaN layers are arranged periodically, wherein the composition of In in the second InGaN layer is 0.32; A P-type GaN layer is disposed on the top surface of the InGaN / GaN quantum well layer.

8. The method for preparing a solar cell epitaxial wafer according to claim 7, characterized in that: The step of preparing the substrate comprises: The substrate is heated in a hydrogen atmosphere using MOCVD equipment.

9. The method for preparing a solar cell epitaxial wafer according to claim 7, characterized in that: The N-type GaN layer is provided on the top surface of the GaN intrinsic layer, comprising: Disposing a GaN layer on the top surface of the GaN intrinsic layer; The GaN layer is doped with Si at a doping concentration of 0.8×10 18 cm -3 -1.2×10 18 cm -3 .

10. The method for preparing a solar cell epitaxial wafer according to claim 7, characterized in that: The P-type GaN layer is provided on the top surface of the InGaN / GaN quantum well layer, comprising: Disposing a GaN layer on the top surface of the InGaN / GaN quantum well layer; Mg is doped into the GaN layer at a doping concentration of 0.8×10 20 cm -3 -1.2×10 20 cm -3 .

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