RADIATION EFFECTS IN GA0.47IN0.53AS DEVICES

The effects of irradiating Ga0.47In0.53As solar cells and p-i-n photodiodes with 1 MeV electrons have been measured using Deep Level Transient Spectroscopy (DLTS) and both dark and illuminated (1 sun, air mass zero (AM0)) current-voltage (I-V) measurements. The I-V measurements were made over the range 100K < T < 450K. Fits of the dark I-V data to the two term diode equation before irradiation were satisfactory, yielding an estimated band-gap energy of 0.79 eV. The recombination component of the dark current was found to increase linearly with fluence. The DLTS detected two radiation-induced defect levels, one shallow (E(c)-0.10 eV) and one near mid-gap (E(c)-0.29 eV). Temperature coefficients of the Ga0.47In0.53As photovoltaic parameters are presented which follow the same general behavior as other solar cell materials (e.g. Si and GaAs). However, a sharp decrease in the short circuit current is observed above almost-equal-to 375 K. This temperature is reduced by irradiation. The radiation-induced degradation of the open circuit voltage is shown to be accurately predicted from the dark I-V measurements. Isochronal thermal annealing induced recovery in the photovoltaic parameters at almost-equal-to 400 K, coinciding with an annealing stage of the near mid-gap defect level. The energy dependence of the nonionizing energy loss (NIEL), which has been shown to be useful in correlating displacement damage in other materials, is calculated here for Ga0.47In0.53As.