Degradation and annealing of electron-irradiated diffused junction InP solar cells

The degradation and annealing properties of 1 MeV electron-irradiated n+p diffused junction InP solar cells are reported in detail. The solar cells were characterized through current–voltage measurements under simulated solar illumination at 1 sun, AM0. The radiation-induced defect spectra were characterized through deep level transient spectroscopy. At fluences up to 1015 cm−2, cell degradation was primarily due to a decrease in the short-circuit current Isc which occurred during the introduction of the hole trap, H4. Most of this degradation could be removed by minority-carrier injection annealing of the H4 defect at temperatures as low as 225 K. At higher irradiation fluences, up to 1016 cm−2, cell degradation was dominated by a decrease in both the open-circuit voltage Voc and the fill factor. This degradation was caused by a large radiation-induced recombination current and by carrier removal which was associated with the introduction of the hole trap H5 and the electron traps EA, EC, and ED. Most of the effects of the recombination current and some of the carrier removal were removed by concurrent injection and thermal annealing between 373 and 400 K where the residual H4 defect concentration and the H5 defect were removed. Essentially full cell recovery was achieved after subsequent annealing between 450 and 500 K where the electron traps also showed a partial annealing stage. Thermal annealing without illumination in the range of 350–500 K showed the same defect annealing stages suggesting that the cell recovery in this temperature range is due solely to thermal annealing. The data are summarized to give a model for the radiation-induced degradation and annealing of these InP solar cells.