Deep-level defects, recombination mechanisms, and their correlation to the performance of low-energy proton-irradiated AlGaAs—GaAs solar cells

A detailed study of deep-level defects, recombination mechanisms, and performance characteristics in low-energy proton-irradiated AlGaAs-GaAs solar cells has been carried out for several proton energies (i.e., 50, 100, 200, and 290 keV) and fluences (i.e., 10¹⁰, 10¹¹, 10¹², and 10¹³p/cm²) using the deep-level transient spectroscopy (DLTS), current-voltage (I-V), capacitance-voltage (C-V), and the scanning-electron microscopy operating in electron-beam induced current (SEM-EBIC) methods. Important defect parameters such as densities and energy levels of defects, thermal emission rates and capture cross sections of electrons and holes in each trap level as well as hole diffusion lengths in n-GaAs LPE layer were determined from these measurements. It is shown that the forward bias dark current was dominated by the recombination of electron-hole pairs via the proton-induced deep-level defects in the junction space-charge region of the cell. The increase in the dark current is directly related to the increase of trap density with increasing proton fluence in the irradiated solar cells. A quantitative correlation between the measured defect parameters and the performance characteristics of the proton-irradiated AlGaAs-GaAs solar cells was obtained from this study.