Proton irradiated heteroepitaxial InP solar cells

Heteroepitaxial InP solar cells, processed using GaAs substrates, were proton irradiated over the energy range from 0.2 to 10 MeV. Results for carrier removal, cell performance and minority carrier diffusion length were found to be separable into either dislocation dominated or energy dependent categories. High dislocation densities were dominant in determining low pre-irradiation minority carrier diffusion lengths and cell efficiencies. In addition, dislocations were dominant in determining the increased radiation resistance and carrier removal rate of heteroepitaxial cells when compared to cells processed on InP substrates. A dislocation related, radiation induced defect level, 0.64 eV below the conduction band, was observed, for the first time, in irradiated heteroepitaxial InP. Energy dependent effects included decreased efficiency, decreased diffusion length and increased carrier removal rate with decreasing proton energy. These latter results were found to be consistent with the energy dependence of proton range in InP