GaAs three-junction cell neutron irradiation joint simulation method based on Geant4 and TCAD

Abstract

The invention discloses a GaAs three-junction cell neutron irradiation joint simulation method based on Geant4 and TCAD, distribution of parameters in a cell is accurately calculated through joint simulation, the distribution is combined with experimental results, a solar cell neutron radiation damage evaluation method is analyzed and improved, and theoretical support is provided for space application of the solar cell neutron radiation damage evaluation method. According to the method, Geant4 and TCAD joint simulation is used for replacing a traditional ground neutron irradiation test, the evaluation period can be remarkably shortened, and the test cost can be reduced. Different fluence and structure parameters can be iterated repeatedly through one-time building of the model, the solar cell on-orbit performance boundary is locked in advance, later reworking and scheduling waiting are reduced, satellites, deep space probes and nuclear power system suppliers are helped to complete reliability verification in the scheme stage, and cost can be reduced continuously and efficiency can be increased continuously.

Description

Technical Field

[0001] This invention belongs to the field of solar cell technology, and particularly relates to a joint simulation method for neutron irradiation of GaAs triple-junction cells based on Geant4 and TCAD. Background Technology

[0002] GaInP / GaAs / Ge triple-junction solar cells possess advantages such as structural stability, high reliability, small size, lightweight, and high photoelectric conversion efficiency, and have been widely used in space power systems. However, in applications such as deep space exploration and lunar base construction, GaInP / GaAs / Ge triple-junction solar cells will be subjected to significant neutron radiation. For example, cosmic rays on the lunar surface interact with lunar regolith to generate a large number of neutrons; furthermore, fission reactors in nuclear-powered spacecraft release a large number of neutrons during operation. These neutrons will cause displacement damage and nuclear transmutation within the cell, inducing deep-level defects and significantly reducing output power and reliability.

[0003] Current research on neutron irradiation damage in GaAs solar cells, both domestically and internationally, primarily focuses on the experimental correlations of radiation-sensitive parameters with neutron flux. There are no reports of joint Geant4 and TCAD simulations of neutron irradiation in triple-junction GaAs cells, resulting in a lack of explanation for the neutron irradiation damage mechanism. Therefore, to gain a deeper understanding of the underlying mechanisms of neutron irradiation, it is urgently necessary to conduct modeling and simulation analysis, investigating the neutron irradiation damage mechanism by analyzing the microscopic distribution characteristics such as carrier concentration, band structure, and recombination rate. Summary of the Invention

[0004] Purpose of the invention: In order to effectively solve the performance degradation problem of GaAs triple-junction solar cells after neutron irradiation, this invention proposes a joint simulation method for neutron irradiation of GaAs triple-junction solar cells based on Geant4 and TCAD. The simulation accurately calculates the distribution of various parameters inside the cell, and combines it with experimental results to analyze and improve the evaluation method of neutron radiation damage of solar cells, providing theoretical support for their space applications.

[0005] Technical solution: The present invention provides a joint simulation method for neutron irradiation of GaAs triple-junction cells based on Geant4 and TCAD, comprising the following steps:

[0006] Step 1: Construct a simulation structure model of GaAs triple-junction solar cell based on the semiconductor process simulation and device simulation tool TCAD;

[0007] Step 2: Combining the physical model and the simulation structural model, construct a simulation model of the electrical characteristics of the GaAs triple-junction battery in TCAD using numerical calculation methods;

[0008] Step 3: calibrate and optimize the electrical parameters of the electrical characteristic simulation model, and construct an electrical simulation model of the GaAs triple junction cell without irradiation based on TCAD;

[0009] Step 4: Based on Geant4, simulate the energy deposition of different neutron fluences, convert it into defect concentration through formula, and input the defect parameters into TCAD to obtain the irradiation simulation model of GaAs triple junction cell under different neutron fluence irradiation conditions.

[0010] Step 5: Analyze the specific distribution of internal parameters of GaAs triple-junction cells based on the neutron irradiation damage model;

[0011] Step 6: Combine the experimental results with the simulation results obtained from the neutron irradiation damage model to study the laws and mechanisms of irradiation damage.

[0012] Further, step 1 specifically involves: constructing a TCAD two-dimensional model based on the battery structure, defining the thickness, doping concentration, doping type, and tunnel junction location of each layer, and adding material parameters for each layer. For material parameters missing from the TCAD software, these parameters are defined to construct a two-dimensional structural model of the triple-junction GaAs battery. The fifth, sixth, eleventh, and twelfth layers are the battery's tunneling layers; these band-to-band tunnels are defined, and the doping concentration of the tunneling layers is 10. 19 cm -3 The doping concentration of the remaining layers is on the order of magnitude of 10. 17 cm -3 -10 18 cm -3 The scale is such that each layer is uniformly doped; the top electrode of the triple-junction GaAs cell is set as the cathode and the bottom electrode as the anode, thus obtaining the simulation structure model of the GaAs triple-junction cell.

[0013] Furthermore, step 2 specifically involves calculating the relevant parameters of a triple-junction solar cell. The theoretical calculations include the Poisson equation and the carrier continuity equation, as shown below:

[0014] div(εΔψ)=-ρ (1)

[0015]

[0016] Equation (1) is the Poisson equation, where ψ is the electrostatic potential, ε is the local dielectric constant, and ρ is the local space charge density; equations (2) and (3) are carrier continuity equations, where R p and R n J represents the recombination rate of holes and electrons, respectively. p and J n G is the current density of holes and electrons, q is the elementary charge, and G is the current density of holes and electrons. n and G pThese are the electron generation rate and hole generation rate, respectively; equations (4) and (5) are drift-diffusion transport equations, where μ p and μ n These are the mobilities of holes and electrons, E, respectively. p and E n These are the quasi-Fermi levels for holes and electrons, respectively;

[0017] By calculating the Poisson equation and the continuity equations for electrons and holes, the relevant parameters of the triple-junction solar cell are solved. Under non-equilibrium conditions, the continuity equations for electrons and holes are:

[0018]

[0019] Where, τ n and τ p These are the average lifetimes of minority carriers in the p-region and the n-region, respectively, D. n and D p G is the diffusion coefficient of electrons and holes. n (x) and G p (x) is the generation rate of electrons and holes, n p It is the excess electron concentration in the p-type region, p n It is the excess hole concentration in the n-type region;

[0020] To simulate nonradiative recombination in the semiconductor bandgap caused by irradiation, the Shockley-Reed-Hall recombination model is used, and its expression is:

[0021]

[0022] Among them, R SRH It is the SRH recombination rate, R A and R D denoted by , respectively, are the recombination rates of acceptor defects and donor defects, and m and n are the numbers of acceptor defects and donor defects, respectively; n i Where is the intrinsic carrier concentration, k is the Boltzmann constant, T is the absolute temperature, g is the degradation factor, and E is the intrinsic carrier concentration. i and E t These are the Fermi level and defect level of intrinsic charge carriers, respectively.

[0023] Furthermore, step 3 specifically involves comparing the electrical parameters obtained from TCAD simulation with the electrical characteristic curves obtained from experiments. By changing the process parameters of the battery's material composition, thickness, and doping concentration of each layer, the model structure is further optimized to obtain the battery's electrical parameters that match the experimental results.

[0024] Further, step 4 specifically involves: simulating energy deposition with different neutron fluences using Geant4, converting the energy deposition into defect concentration using a formula, and inputting the defect parameters into TCAD to obtain an irradiation simulation model of the GaAs triple-junction cell under different neutron fluence irradiation conditions: the defect density is obtained through the non-ionization energy deposition calculated using G4, i.e.:

[0025]

[0026] In the formula: D T 1 is the defect density, NIEL is the non-ionization energy loss, Ed is the displacement energy, which is the minimum energy required for an atom to leave the crystal lattice, and V is the volume.

[0027] Furthermore, in step 6: the study of the laws and mechanisms of irradiation damage includes both macroscopic and microscopic levels; at the macroscopic level, the irradiation conditions that cause more severe irradiation damage to the battery are obtained through IV characteristic curves; at the microscopic level, the changes of various parameters inside the battery after irradiation are obtained through simulated damage models.

[0028] The present invention also discloses a computer device, including a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the method of the present invention.

[0029] The present invention also discloses a computer-readable storage medium having a computer program / instructions stored thereon, which, when executed by a processor, implements the steps of the method of the present invention.

[0030] The present invention also discloses a computer program product, including a computer program / instructions that, when executed by a processor, implement the steps of the method of the present invention.

[0031] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0032] This invention proposes a joint simulation method for neutron irradiation of GaAs triple-junction solar cells based on Geant4 and TCAD. Through matching and optimization with experimental results, the method achieves high model accuracy. Simulation analysis of the electrical performance and internal parameters allows for a more accurate assessment of the irradiation damage suffered by GaAs triple-junction solar cells, providing theoretical support for elucidating the laws and mechanisms of neutron irradiation damage. Furthermore, the neutron irradiation simulation model can predict the degradation trend of the cells after irradiation with different neutron fluxes, reducing the time required for ground-based evaluation experiments and significantly lowering the economic cost of ground-based simulation tests.

[0033] This invention replaces traditional ground-based neutron irradiation experiments with joint simulation using Geant4 and TCAD, significantly shortening the evaluation cycle and reducing experimental costs. The model can be built once and iterated repeatedly with different flux and structural parameters, allowing for early determination of the on-orbit performance boundaries of solar cells. This reduces rework and scheduling delays, helping satellite, deep space probe, and nuclear power system suppliers complete reliability verification during the design phase, leading to sustainable cost reduction and efficiency improvement. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the process of the present invention;

[0035] Figure 2 This is a schematic diagram of the GaAs triple-junction battery structure of the present invention;

[0036] Figure 3 This is a modeling diagram of the GaAs triple-junction battery of the present invention;

[0037] Figure 4 This is a comparison of experimental and simulation results of the IV curve of the GaAs triple-junction cell of this invention without irradiation;

[0038] Figure 5 The results of Geant4 simulation of the GaAs triple junction cell irradiated according to the present invention are the energy deposition results.

[0039] Figure 6 This is a comparison of experimental and simulation curves of the GaAs triple-junction cell before and after irradiation according to the present invention.

[0040] Figure 7 This is a diagram showing the electron concentration distribution inside the GaAs triple-junction battery of the present invention.

[0041] Figure 8 This is a hole concentration distribution diagram inside the GaAs triple-junction battery of the present invention;

[0042] Figure 9 This is a diagram showing the internal recombination rate distribution of the GaAs triple-junction battery of the present invention.

[0043] Figure 10 This invention relates to the internal band structure distribution of the GaAs triple-junction battery. Detailed Implementation

[0044] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0045] like Figure 1 As shown, this invention proposes a joint simulation method for neutron irradiation of GaAs triple-junction cells based on Geant4 and TCAD, comprising the following steps:

[0046] (1) Based on the battery structure, a two-dimensional TCAD model was constructed, defining the thickness, doping concentration, doping type, and tunnel junction location of each layer. Material parameters for each layer were added, and material parameters not present in the TCAD software were defined to construct a two-dimensional structural model of the triple-junction GaAs battery. Specifically, based on... Figure 2 The structure diagram of the GaAs triple-junction solar cell is shown. A two-dimensional model of the cell is constructed using TCAD. The fifth, sixth, eleventh, and twelfth layers are the tunneling layers of the cell. These band-to-band tunnels are defined, and the doping concentration of the tunneling layers is 10. 19 cm -3 The doping concentration of the remaining layers is on the order of magnitude of 10. 17 cm -3 -10 18 cm -3 The order of magnitude is similar, with each layer uniformly doped. A simulation model of the GaAs triple-junction cell is obtained by setting the top electrode as the cathode and the bottom electrode as the anode.

[0047] (2) Figure 3 As shown, the physical models required for the battery are added, and a bias voltage is applied to the battery anode. The electrical characteristic curves of the battery are obtained through numerical calculations. The physical models include the Shockley-Read-Hall (SRH) recombination model, the Poisson equation, the continuity equation, the Standard Auger Model (Auger) recombination model, the Fermi-Dirac carrier statistical model, the Conmob concentration-dependent mobility model, the Optical Recombination Model (Optr), the Bandgap Narrowing (Bgn) carrier statistical model, and the Band-to-band Tunneling (Bbt) model. The NEWTON iterative method is used for numerical calculations.

[0048] To calculate the relevant parameters of a triple-junction solar cell, the theoretical calculations involve the Poisson equation and the carrier continuity equation, as shown below:

[0049] div(εΔψ)=-ρ (1)

[0050]

[0051] Equation (1) is the Poisson equation, where ψ is the electrostatic potential, ε is the local dielectric constant, and ρ is the local space charge density. Equations (2) and (3) are the carrier continuity equations, where R... p and R n J represents the recombination rate of holes and electrons, respectively. p and J nμ is the current density of holes and electrons, and q is the elementary charge. Equations (4) and (5) are the drift-diffusion transport equations, where μ p and μ n These are the mobilities of holes and electrons, E, respectively. p and E n These are the quasi-Fermi levels for holes and electrons, respectively.

[0052] By calculating the Poisson equation and the continuity equations for electrons and holes, the relevant parameters of a triple-junction solar cell can be solved. In the non-equilibrium state, the continuity equations for electrons and holes are:

[0053]

[0054] Where, τ n and τ p D represents the average lifetime of minority carriers (electrons) in the p-region and the average lifetime of minority carriers (holes) in the n-region, respectively. n and D p G is the diffusion coefficient of electrons and holes. n (x) and G p (x) is the generation rate of electrons and holes.

[0055] To simulate nonradiative recombination in the semiconductor bandgap caused by irradiation, the Shockley-Reed-Hall (SRH) recombination model is used, and its expression is as follows:

[0056]

[0057] Among them, R SRH It is the SRH recombination rate, R A and R D , where are the recombination rates of acceptor defects and donor defects, respectively, and m and n are the number of acceptor defects and donor defects, respectively. i Where is the intrinsic carrier concentration, k is the Boltzmann constant, T is the absolute temperature (K), g is the degradation factor, and E is the intrinsic carrier concentration. i and E t These are the Fermi level and defect level of intrinsic charge carriers, respectively.

[0058] (3) Compare the electrical parameters obtained from the TCAD simulation in step (2) with the electrical characteristic curves obtained from the experiment. Further optimize the model structure by changing the process parameters such as the battery material composition, thickness, and doping concentration of each layer of material to obtain the battery electrical parameters that match the experimental results. The deviation between the two is less than 5%. The electrical parameters include typical electrical parameters such as the battery's open-circuit voltage and short-circuit current. Figure 4 As shown, an electrical simulation model of a GaAs triple-junction cell without irradiation is obtained.

[0059] (4) Based on Geant4 simulation of energy deposition with different neutron fluences, the energy is converted into defect concentration using a formula. The defect parameters are then input into TCAD to obtain irradiation simulation models of GaAs triple-junction cells under different neutron fluence irradiation conditions:

[0060] The defect density can be obtained using the non-ionization energy deposition calculated by G4, i.e.:

[0061]

[0062] In the formula: D T 1 is the defect density, NIEL is the non-ionization energy loss, Ed is the displacement energy, which is the minimum energy required for an atom to leave the crystal lattice, and V is the volume.

[0063] Therefore, by means of equation (11) and Figure 5 The energy deposition results calculated by G4 shown can be used to calculate the defect density required for TCAD.

[0064] By inputting the defect information into TCAD for simulation, a neutron irradiation simulation model of the battery under different irradiation flux conditions can be obtained, and the simulation results can be further optimized by combining the experimental results. Figure 6 The figure shows a comparison between the experimental and simulated IV curves before and after irradiation. It can be seen that the simulation results are in good agreement with the experimental results. Therefore, the accuracy of the neutron irradiation simulation model has been verified.

[0065] (5) The specific distribution of internal parameters of GaAs triple junction cells is obtained based on the neutron irradiation damage model. Figure 7 and Figure 8 These are the electron concentration distribution and hole concentration distribution, respectively. Figure 9 The composite rate distribution is as follows: Figure 10 This represents the distribution of the band structure.

[0066] By combining experimental results with simulation results derived from a neutron irradiation damage model, the laws and mechanisms of irradiation damage are studied. Combining experimental and simulation results, we can determine, at the macroscopic level (IV characteristic curve), which irradiation conditions cause more severe battery damage. Furthermore, at the microscopic level, the changes in various internal parameters of the battery after irradiation can be obtained through the simulated damage model. Combined with the macroscopic conclusions, we can further study the laws and mechanisms of irradiation damage. Figure 7 and Figure 8 The figures show the electron concentration distribution and hole concentration distribution, respectively. It can be seen from the figures that the electron concentration in the junction region and the base region of the GaInP top cell and the GaAs middle cell are significantly reduced. This is because the base region is P-type doped, and the minority carriers are electrons. Non-radiative recombination mainly leads to a decrease in minority carrier concentration, with the GaAs cell showing the most severe decrease in carrier concentration. Figure 9The figure shows the recombination rate distribution. As the neutron flux increases, the recombination rate of the GaInP top cell base region increases the most significantly, while the recombination rate of the GaAs middle cell junction region increases first and then decreases. Figure 10 The figure shows the band structure distribution. As the neutron flux increases, the band structure of the GaAs cell shifts upward, indicating that displacement damage mainly occurs in the GaAs cell.

Claims

1. A method for joint simulation of neutron irradiation of GaAs triple-junction cells based on Geant4 and TCAD, characterized in that, Comprising the following steps: Step 1, based on semiconductor process simulation and device simulation tool TCAD, a simulation structure model of GaAs three-junction cell is constructed; Step 2, combining physical model and simulation structure model, an electrical characteristic simulation model of GaAs three-junction cell is constructed in TCAD through numerical operation method; Step 3, the electrical parameters of the electrical characteristic simulation model are calibrated and optimized, and an electrical simulation model of GaAs three-junction cell under non-irradiation is constructed based on TCAD; Step 4, based on Geant4 simulation of energy deposition of different neutron fluences, the defect concentration is converted through formula, and the defect parameters are input into TCAD to obtain an irradiation simulation model of GaAs three-junction cell under different neutron fluence irradiation conditions; Step 5, according to the neutron irradiation damage model, the specific distribution of the internal parameters of the GaAs three-junction cell is analyzed; Step 6, combining the results obtained by the experiment and the simulation results obtained by the neutron irradiation damage model, the irradiation damage law and mechanism are studied.

2. The combined simulation method of GaAs triple-junction cell neutron irradiation based on Geant4 and TCAD according to claim 1, characterized in that, The step 1 is specifically: constructing a TCAD two-dimensional model according to the battery structure, defining the thickness, doping concentration, doping type and tunnel junction position of each layer, and adding the material parameters of each layer material, defining the material parameters lacking in the TCAD software, and constructing a two-dimensional structure model of the three-junction GaAs battery; the materials of the fifth layer, the sixth layer, the eleventh layer and the twelfth layer are the tunnel layers of the battery, the band-to-band tunneling is defined, the doping concentration of the tunnel layer is 10 19 cm -3 order of magnitude, the doping concentration of the remaining layers is 10 17 cm -3 -10 18 cm -3 order of magnitude, each layer is uniformly doped; the top electrode of the three-junction GaAs battery is set as the cathode, and the bottom electrode of the battery is set as the anode, to obtain a simulation structure model of the GaAs three-junction battery.

3. The combined simulation method of GaAs triple-junction cell neutron irradiation based on Geant4 and TCAD according to claim 1, characterized in that, Step 2 is specifically: to calculate the related parameters of the three-junction solar cell, the equations included in the theoretical calculation are Poisson equation and carrier continuity equation, as follows: div (εΔψ) = -ρ (1) Wherein equation (1) is Poisson equation, ψ is electrostatic potential, ε is local dielectric constant, and ρ is local space charge density; Equations (2) and (3) are carrier continuity equations, where R p and R n are the recombination rates of holes and electrons, respectively, J p and J n are the current densities of holes and electrons, q is the elementary charge, G n and G p are the electron and hole generation rates, respectively; and equations (4) and (5) are drift-diffusion transport equations, where μ p and μ n are the mobilities of holes and electrons, respectively, E p and E n are the quasi-Fermi levels of holes and electrons, respectively; By calculating the Poisson equation and the continuity equation of electrons and holes, the related parameters of the three-junction solar cell are solved, and in a non-equilibrium state, the continuity equation of electrons and holes is: where τ n and τ p are the average lifetimes of the minority carriers in the p and n regions, respectively, D n and D p are the diffusion coefficients of the electrons and holes, G n (x) and G p (x) are the generation rates of the electrons and holes, n p is the excess electron concentration in the p-type region, and p n is the excess hole concentration in the n-type region. To simulate the non-radiative recombination in the semiconductor band gap caused by irradiation, the Shockley-Reed-Hall recombination model is used, and its expression is: where R SRH is the SRH recombination rate, R A and R D are the recombination rates of acceptor and donor defects, respectively, m and n are the number of acceptor and donor defects, respectively; n i is the intrinsic carrier concentration, k is the Boltzmann constant, T is the absolute temperature, g is the degradation factor, E i and E t are the Fermi level of intrinsic carriers and defect level, respectively.

4. The combined simulation method of GaAs triple-junction cell neutron irradiation based on Geant4 and TCAD according to claim 1, characterized in that, Step 3 is specifically: comparing the electrical parameters obtained by TCAD simulation with the electrical characteristic curve results obtained by experiment, further optimizing the model structure by changing the process parameters of the material composition, thickness and doping concentration of each layer of the cell, and obtaining the electrical parameters of the cell matched with the experimental results.

5. The combined simulation method of GaAs triple-junction cell neutron irradiation based on Geant4 and TCAD according to claim 1, characterized in that, Step 4 is specifically: based on Geant4 simulation of energy deposition of different neutron fluences, the defect concentration is converted through formula, and the defect parameters are input into TCAD to obtain an irradiation simulation model of GaAs three-junction cell under different neutron fluence irradiation conditions: the defect density is obtained by non-ionizing energy deposition calculated by G4, that is: where D T is the defect density, NIEL is the non-ionizing energy loss, Ed is the dislocation energy, i.e. the minimum energy to remove an atom from the lattice, and V is the volume.

6. The combined simulation method of GaAs triple-junction cell neutron irradiation based on Geant4 and TCAD according to claim 1, characterized in that, In step 6: the irradiation damage law and mechanism research includes macroscopic and microscopic levels; the macroscopic level obtains the irradiation condition that makes the cell irradiation damage more serious through the I-V characteristic curve; the microscopic level obtains the changes of each parameter inside the cell after irradiation through the simulated damage model.

7. A computer apparatus comprising a memory, a processor, and a computer program stored on the memory, wherein the computer program, when executed by the processor, causes the processor to perform the method of any one of claims 1 to 6. The processor executes the computer program to realize the steps of the method of claim 1.

8. A computer readable storage medium having stored thereon computer programs / instructions, characterized in that, The computer program / instructions are executed by the processor to realize the steps of the method of claim 1.

9. A computer program product comprising computer programs / instructions, characterized in that, The computer program / instructions are executed by the processor to realize the steps of the method of claim 1. The computer program / instructions are executed by the processor to realize the steps of the method of claim 1.

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