ANNEALING OF IRRADIATED EPITAXIAL INP SOLAR-CELLS

The annealing behavior of electron, proton, and alpha particle irradia ted, epitaxial n(+)p InP solar cells has been characterized using seve ral techniques. Current-voltage measurements were made under simulated 1 sun, AM0 solar illumination and in the dark. The radiation-induced defect spectra were monitored using deep level transient spectroscopy and the base carrier concentration profiles were determined through ca pacitance-voltage measurements. The irradiated cells were annealed at temperatures ranging from 300 up to 500 K. Some cells were annealed wh ile under illumination at short circuit while others were annealed in the dark. These experiments produced essentially the same results inde pendent of illumination and independent of the irradiating particle. A n annealing stage was observed between 400 and 500 K, in which the rad iation-induced defects labeled H3 and H4 were removed and the carrier concentration recovered slightly, Concurrently there was a small reduc tion in the junction recombination current and a slight increase in th e photovoltaic (PV) output of the cell; however, most of the radiation -induced defects did not anneal, and the overall PV recovery was very small. A full analysis of the annealing data is given, and a model for the radiation response and annealing behavior of the cells is present ed. The results are compared to those reported previously for irradiat ed, diffused junction InP solar cells. Although the radiation-induced degradation mechanisms appear to be essentially the same in the two ee l types, the recovery of the PV output is found to be quite different. This difference in cell recovery is explained in terms of the defect annealing characteristics in the individual cell types. (C) 1996 Ameri can Institute of Physics.