Understanding efficiency improvements of betavoltaic batteries based on 4H-SiC, GaN, and diamond

Wide-bandgap semiconductors are more advantageous for betavoltaic batteries due to their high conversion efficiency and strong radiation resistance. However, there has been little comprehensive analysis of how wide-bandgap semiconductors lead to efficiency improvements. In this work, we proposed a simulation model to predict the output performance of betavoltaic batteries based on 4H-SiC, hexagonal-GaN, and diamond, in which the Monte Carlo code and COMSOL Multiphysics software were combined. The energy deposition of a 63Ni source in semiconductors and the electrical characteristics of p–n junctions were investigated and compared. Our simulation results showed that the mass density and atomic number of semiconductor materials will cause the difference in energy deposition distribution, further leading to the different electron–hole pair generation rates. Then, the internal efficiency of batteries is co-determined by the energy band structure, depletion region width, built-in potential barrier, and minority carrier lifetime. The batteries based on wide-bandgap semiconductors can achieve the larger open-circuit voltage, further leading to higher efficiency. Additionally, to optimize the energy converter structure, the output parameters were calculated with a variation of doping concentrations and thicknesses of each region. Under the irradiation of a 63Ni source, the diamond-based battery with a p–n junction structure has the highest internal efficiency of 31.3%, while the GaN-based battery has the lowest one (16.8%), which can be attributed to the larger carrier recombination rate.