Junction characteristics of electron-irradiated Ga0.5In0.5P n+-p diodes and solar cells

The effects of 1 MeV electron irradiation on n+-p mesa diodes and solar cells fabricated from metalorganic chemical vapor deposition grown Ga0.5In0.5P on GaAs have been studied. Upon electron irradiation, Ga0.5In0.5P n+-p junction dark current increased by more than one order of magnitude, but it could be reduced by about 75% after annealing at 250 °C for 10 min. The increase in junction dark current was mainly attributed to reductions in minority carrier lifetimes. It was also found that Ga0.5In0.5P solar cell open-circuit voltage, short-circuit current, fill factor, and air-mass zero conversion efficiency were all reduced on the average by 11%, 18%, 8%, and 33%, respectively, following exposure to 1016 electrons/cm2. However, a significant improvement in the electron-irradiated Ga0.5In0.5P solar cell efficiency was observed via thermal annealing at 250 °C, demonstrating good potential for a longer solar cell lifetime in space through on-orbit thermal annealing. The degradation in solar cell conversion efficiency following 1 MeV electron irradiation was smaller than that observed in Si and GaAs, but greater than that in InP solar cells.