Gallium arsenide solar cell with germanium substrate for space and preparation method of gallium arsenide solar cell

Abstract

The invention provides a space germanium substrate gallium arsenide solar cell and a preparation method thereof, and the preparation method at least comprises the steps: preparing a first germanium-based epitaxial wafer which is provided with a germanium substrate with a basic thickness; performing rough grinding, stress annealing, plastic accurate grinding and chemical corrosion on the germanium substrate side of the first germanium-based epitaxial wafer in sequence to obtain a fourth germanium-based epitaxial wafer which is provided with a germanium substrate with a third target thickness; wherein during plastic fine grinding, micro-current pulses are applied to a fine grinding area through a closed loop formed by fine grinding equipment and the second germanium-based epitaxial wafer obtained through coarse grinding. According to the preparation method, a process route of combining temporary bonding support, step-by-step mechanical thinning and low-temperature chemical corrosion is adopted after epitaxial growth, so that reliable preparation of the ultrathin germanium substrate is realized on the basis of keeping the initial thickness of the germanium substrate to ensure the epitaxial quality; and a reliable technical scheme is provided for the preparation of a space-used efficient light-weight solar cell.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, and in particular to a gallium arsenide solar cell with a germanium substrate for space use and its preparation method. Background Technology

[0002] Currently, in spacecraft power systems, gallium arsenide solar cells based on germanium substrates have gradually replaced traditional monocrystalline silicon solar cells for space use due to their high photoelectric conversion efficiency and excellent reliability, becoming an important component of spacecraft primary power supplies and significantly improving the payload capacity and on-orbit lifespan of spacecraft. In existing technologies, the most mature and widely used space solar cell products are germanium-based triple-junction solar cells, with typical germanium substrate thicknesses of 145 μm or 175 μm. However, the thicker substrate results in a lower power-to-weight ratio for the solar cells, making it difficult to meet the increasingly urgent demand for lightweight power systems in modern spacecraft.

[0003] To achieve thinner and lighter solar cells, directly using excessively thin germanium substrates for epitaxial growth is not feasible. This is because during epitaxy, the substrate needs sufficient mechanical strength to withstand high temperatures and epitaxial stress. Substrates that are too thin are prone to warping and breakage, leading to a significant decrease in epitaxial yield. Therefore, achieving lightweight solar cells while ensuring epitaxial quality has become a key technological challenge. Current technologies typically involve thinning the wafer after epitaxial growth, but conventional thinning processes easily introduce mechanical damage, residual stress, and microscopic defects, thus affecting the mechanical integrity and electrical performance of the cell. Summary of the Invention

[0004] The purpose of this invention is to provide a gallium arsenide solar cell with a germanium substrate for space use and a method for its fabrication, so as to solve the problems in the background art.

[0005] The technical solution adopted in this invention includes: a method for preparing a gallium arsenide solar cell on a germanium substrate for space use, which includes at least the following steps:

[0006] Prepare a first germanium-based epitaxial wafer, wherein the first germanium-based epitaxial wafer has a germanium substrate of basic thickness;

[0007] The first germanium-based epitaxial wafer is subjected to rough grinding, stress annealing, plastic fine grinding and chemical etching in sequence on the germanium substrate side to obtain the fourth germanium-based epitaxial wafer, which has a germanium substrate with a third target thickness.

[0008] During plastic fine grinding, a micro-current pulse is applied to the fine grinding area through a closed loop consisting of the fine grinding equipment and the second germanium-based epitaxial wafer obtained from coarse grinding.

[0009] Preferably, the current density of the microcurrent pulse is 0.1~1A / cm2, and the frequency is 10~100Hz.

[0010] Preferably, a third germanium-based epitaxial wafer is obtained by plastic grinding. The third germanium-based epitaxial wafer has a germanium substrate with a second target thickness, and the difference between the second target thickness and the third target thickness is 10 μm to 15 μm.

[0011] Preferably, the second germanium-based epitaxial wafer has a germanium substrate with a first target thickness, and the difference between the first target thickness and the second target thickness is 50 μm.

[0012] Preferably, during rough grinding: the temperature of the first germanium-based epitaxial wafer is 13~17℃, the grit size of the diamond grinding wheel is 320~500 mesh, the rotation speed is 300~500rpm, and the feed rate is 50~100μm / min.

[0013] Preferably, during plastic grinding: the diamond grinding wheel has a particle size of 2000~3000 mesh, a rotation speed of 1500~5000 rpm, and a feed rate of less than 100 μm / min.

[0014] Preferably, during stress annealing: the second germanium-based epitaxial wafer is annealed in an inert gas atmosphere at a temperature of 300~450℃ for 30~90 seconds.

[0015] Preferably, during chemical corrosion: the corrosive solution contains hydrofluoric acid, nitric acid and acetic acid, and the corrosion temperature is 0~15℃.

[0016] Preferably, before rough grinding on the germanium substrate side of the first germanium-based epitaxial wafer, a rigid carrier plate is bonded to the epitaxial structure side of the first germanium-based epitaxial wafer. The thickness of the bonding adhesive used to bond the rigid carrier plate is 30~100μm, and the elastic modulus at 80~120℃ is 3~10GPa.

[0017] The technical solution of the present invention also includes: a gallium arsenide solar cell with a germanium substrate for space use, which is prepared by the above-mentioned method for preparing a gallium arsenide solar cell with a germanium substrate for space use.

[0018] The beneficial effects of this invention are as follows: By employing a process route combining temporary bonding support, stepwise mechanical thinning, and low-temperature chemical etching after epitaxial growth, reliable fabrication of ultrathin germanium substrates is achieved while maintaining the initial thickness of the germanium substrate to ensure epitaxial quality. Specifically, stress annealing introduced after rough grinding effectively repairs crystal damage defects; the application of microcurrent pulse-induced electroplasticity during the fine grinding stage significantly reduces microscopic damage and grinding-induced stress during the grinding process; and finally, controlled low-temperature chemical etching removes the damaged layer and precisely controls the thickness. This process system achieves lightweight solar cell substrates while ensuring structural integrity and electrical performance, solving the problem of balancing damage control and thickness uniformity in existing thinning technologies, and providing a reliable technical solution for the fabrication of high-efficiency, lightweight solar cells for space applications. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] This invention provides a method for fabricating a gallium arsenide solar cell on a germanium substrate for space use, and the gallium arsenide solar cell on a germanium substrate for space use obtained by this method. The fabrication method includes the following steps:

[0021] S1. Prepare a first germanium-based epitaxial wafer. The first germanium-based epitaxial wafer has a germanium substrate with a basic thickness of 145 μm or more to ensure the mechanical strength of the substrate required for the epitaxial process, so as to avoid warping and breakage.

[0022] Specifically, in this step, a GaInP nucleation layer, a GaInAs buffer layer, a first tunnel junction, a lattice gradient buffer layer, an overshoot layer, a GaInAs subcell, a second tunnel junction, an AlGaInP subcell, and a GaInAs cap layer are sequentially epitaxially grown on a P-type germanium substrate using MOCVD technology, thereby forming a first germanium-based epitaxial wafer with an AlGaInP / InGaAs / Ge stacked structure.

[0023] Then, the upper metal electrode and antireflection film of the battery are fabricated on the epitaxial structure side of the first germanium-based epitaxial wafer according to known battery device technology.

[0024] S2. The epitaxial structure of the first germanium-based epitaxial wafer containing the metal electrode and antireflection film obtained in step S1 is bonded to a rigid carrier plate.

[0025] Specifically, in this step, a temporary bonding adhesive with ultraviolet laser dissociation is used to temporarily bond the first germanium-based epitaxial wafer to a rigid substrate. The thickness of the bonding adhesive is controlled between 30 μm and 100 μm, and the bonding adhesive has an elastic modulus of 3 to 10 GPa at 80 to 120°C to match the elastic modulus characteristics of the germanium substrate in this temperature range, thereby providing effective stress buffering and support.

[0026] S3. The germanium substrate side of the first germanium-based epitaxial wafer bonded with a rigid carrier plate obtained in step S2 is rough ground.

[0027] Specifically, in this step, the first germanium-based epitaxial wafer is placed on the temperature-controlled bearing plate of the grinding machine, and the temperature of the germanium substrate side is controlled at 13~17℃. Then, a diamond grinding wheel with a grit size of 320~500 mesh is used to grind the germanium substrate side of the first germanium-based epitaxial wafer at a speed of 300~500 rpm and a feed rate of 50~100 μm / min, removing most of the thickness of the germanium substrate to obtain the second germanium-based epitaxial wafer. The thickness of the germanium substrate of the second germanium-based epitaxial wafer is reduced to a preset intermediate thickness for subsequent plastic fine grinding process, i.e., the first target thickness.

[0028] S4. Stress annealing is performed on the second germanium-based epitaxial wafer obtained in step S3.

[0029] Specifically, in this step, the second germanium-based epitaxial wafer is placed in an inert gas (e.g., nitrogen) atmosphere, and the temperature is controlled at 300~450℃ for 30~90 seconds to perform rapid thermal annealing on the second germanium-based epitaxial wafer in order to repair crystal damage defects introduced by the rough grinding process and release macroscopic stress.

[0030] S5. Perform plastic fine grinding on the annealed second germanium-based epitaxial wafer obtained in step S4.

[0031] Specifically, in this step, a diamond grinding wheel with a grit size of 2000-3000 mesh is used to grind the germanium substrate side of the second germanium-based epitaxial wafer at a rotation speed of 1500-5000 rpm and a feed rate of <100 μm / min. The germanium substrate of the second germanium-based epitaxial wafer and the diamond grinding wheel are connected to form a closed circuit, and a current density of 0.1-1 A / cm is applied to the fine-grinding area through this circuit. 2 A microcurrent pulse with a frequency of 10~100Hz generates an electroplastic effect in the contact area between the germanium substrate and the grinding wheel, reducing the yield strength of the material and causing the germanium substrate material to undergo plastic flow under lower mechanical stress. This significantly reduces the depth of the micro-damage layer and the grinding-induced stress while efficiently removing the material.

[0032] After the above processing, a third germanium-based epitaxial wafer is obtained. The thickness of the germanium substrate of the third germanium-based epitaxial wafer is reduced to a preset intermediate thickness for subsequent chemical thinning processes, namely the second target thickness.

[0033] S6. Perform chemical thinning on the third germanium-based epitaxial wafer obtained in step S5.

[0034] Specifically, in this step, the third germanium-based epitaxial wafer is placed in an acidic etching solution containing hydrofluoric acid, nitric acid, and acetic acid in a volume ratio of 1:4:10. By controlling the temperature of the etching solution within a low temperature range of 0~15℃, the generation of thermal stress during the etching process is suppressed. A stirring device is used to keep the concentration and temperature of the etching solution uniform, thereby performing controlled chemical etching on the germanium substrate of the third germanium-based epitaxial wafer to remove the structural damage layer formed by the mechanical thinning in the aforementioned steps, until the target substrate thickness is reached, resulting in a fourth germanium-based epitaxial wafer with a germanium substrate of the third target thickness.

[0035] Preferably, the difference between the first target thickness and the second target thickness is 50 μm, and the difference between the second target thickness and the third target thickness is 10~15 μm. This setting is based on the following process considerations: mechanical thinning process has better thickness uniformity control capability and is suitable for removing larger thicknesses; while chemical thinning process has relatively poor consistency of etching rate between the wafer center and the edge. By controlling its thinning thickness within a small range (10~15 μm), the thickness non-uniformity introduced by it can be effectively reduced, thereby ensuring the overall uniformity of the final substrate thickness.

[0036] After thinning, the fourth germanium-based epitaxial wafer is cleaned. During cleaning, low-frequency megasonic energy is first applied to the cleaning tank to enhance the cleaning effect without damaging the fragile wafer. Then, the final rinsing and drying are performed. Low surface tension solvents (such as IPA) are used for Marangoni effect drying to prevent water stains and reduce electrostatic forces.

[0037] Then, Au / Ge / Ag / Au metal lower electrode is deposited on the fourth germanium-based epitaxial wafer. After the lower electrode is deposited, the rigid carrier plate and the fourth germanium-based epitaxial wafer are debonded: the temporary bonding adhesive is irradiated through the transparent carrier plate with ultraviolet laser to make it lose its adhesiveness, and the ultrathin fourth germanium-based epitaxial wafer is separated without damage.

[0038] After inspecting the epitaxial wafer thickness, total thickness variation, warpage, and back-side defects, the fourth germanium-based epitaxial wafer is placed in a dicing machine and diced according to the designed dimensions to obtain a gallium arsenide solar cell with a germanium substrate for space use.

[0039] Compared with existing technologies, the beneficial effects of this invention include at least the following: by employing a process route combining temporary bonding support, stepwise mechanical thinning, and low-temperature chemical etching after epitaxial growth, reliable fabrication of ultrathin germanium substrates is achieved while maintaining the initial thickness of the germanium substrate to ensure epitaxial quality. Specifically, stress annealing introduced after rough grinding effectively repairs crystal damage defects; the application of microcurrent pulse-induced electroplasticity during the fine grinding stage significantly reduces microscopic damage and grinding-induced stress during the grinding process; and finally, controlled low-temperature chemical etching removes the damaged layer and precisely controls the thickness. This process system achieves lightweight solar cell substrates while ensuring structural integrity and electrical performance, solving the problem of balancing damage control and thickness uniformity in existing thinning technologies, and providing a reliable technical solution for the fabrication of high-efficiency, lightweight solar cells for space applications.

[0040] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the claims, or equivalent forms of such scope and boundaries.

Claims

1. A method for fabricating a gallium arsenide solar cell on a germanium substrate for space use, characterized in that, At least the following steps are included: Prepare a first germanium-based epitaxial wafer, wherein the first germanium-based epitaxial wafer has a germanium substrate of basic thickness; The first germanium-based epitaxial wafer is subjected to rough grinding, stress annealing, plastic fine grinding and chemical etching in sequence on the germanium substrate side to obtain the fourth germanium-based epitaxial wafer, which has a germanium substrate with a third target thickness. During plastic fine grinding, a micro-current pulse is applied to the fine grinding area through a closed loop consisting of the fine grinding equipment and the second germanium-based epitaxial wafer obtained from coarse grinding.

2. The method for fabricating a gallium arsenide solar cell on a germanium substrate for space use according to claim 1, characterized in that, The current density of the microcurrent pulse is 0.1~1 A / cm. 2 The frequency is 10~100Hz.

3. The method for fabricating a gallium arsenide solar cell on a germanium substrate for space use according to claim 1 or 2, characterized in that, A third germanium-based epitaxial wafer is obtained by plastic grinding. The third germanium-based epitaxial wafer has a germanium substrate with a second target thickness. The difference between the second target thickness and the third target thickness is 10 μm to 15 μm.

4. The method for fabricating a gallium arsenide solar cell on a germanium substrate for space use according to claim 3, characterized in that, The second germanium-based epitaxial wafer has a germanium substrate with a first target thickness, the difference between the first target thickness and the second target thickness being 50 μm.

5. The method for fabricating a gallium arsenide solar cell on a germanium substrate for space use according to claim 4, characterized in that, During rough grinding: the temperature of the first germanium-based epitaxial wafer is 13~17℃, the grit size of the diamond grinding wheel is 320~500 mesh, the rotation speed is 300~500rpm, and the feed rate is 50~100μm / min.

6. The method for fabricating a gallium arsenide solar cell on a germanium substrate for space use according to claim 4, characterized in that, For plastic grinding: the diamond grinding wheel has a grit size of 2000~3000 mesh, a rotation speed of 1500~5000 rpm, and a feed rate of <100μm / min.

7. The method for fabricating a gallium arsenide solar cell on a germanium substrate for space use according to any one of claims 1-2 and 4-6, characterized in that, During stress annealing: The second germanium-based epitaxial wafer is annealed in an inert gas atmosphere at a temperature of 300~450℃ for 30~90 seconds.

8. The method for fabricating a gallium arsenide solar cell on a germanium substrate for space use according to claim 6, characterized in that, During chemical corrosion: the corrosive solution contains hydrofluoric acid, nitric acid and acetic acid, and the corrosion temperature is 0~15℃.

9. The method for fabricating a gallium arsenide solar cell on a germanium substrate for space use according to any one of claims 1-2, 4-6, and 8, characterized in that, Before rough grinding on the germanium substrate side of the first germanium-based epitaxial wafer, a rigid carrier plate is bonded to the epitaxial structure side of the first germanium-based epitaxial wafer. The thickness of the bonding adhesive used to bond the rigid carrier plate is 30~100μm, and the elastic modulus at 80~120℃ is 3~10GPa.

10. A gallium arsenide solar cell with a germanium substrate for space use, characterized in that, It is prepared by the method of any one of claims 1-9 for the fabrication of gallium arsenide solar cells on germanium substrates for space use.