BASE DOPING OPTIMIZATION FOR RADIATION-HARD SI, GAAS, AND INP SOLAR-CELLS

This paper shows that the nature of radiation-induced point defects and dopant interactions can cause a shift in the optimum base doping concentration for terrestrial and space solar cells. The base doping concentration has been optimized for high-efficiency Si, GaAs, and InP solar cells before and after electron irradiation. A combination of detailed carrier lifetime calculations and cell modeling is used to show that the optimum doping concentration for irradiated cells increases for InP cells, decreases for Si cells, and remain essentially unchanged for GaAs cells compared to their counterpart terrestrial cells. The optimum base doping for Si cells decreases from 8.94 x 10(16) cm-3 to approximately 6.6 x 10(14) cm-1 after 1-MeV electron irradiation. In the case of GaAs, the optimum base doping concentration remains at approximately 2 x 10(17) cm-3 for both irradiated and unirradiated cells. In contrast to Si and GaAs cells, the InP base doping needs to be increased in the range of 2-6 x 10(17) cm-3 from 2 x 10(17) cm-3 for radiation fluences in the range of 10(15) to 10(16) cm-2 in order to achieve highest efficiency after irradiation.