Effects of electron beam irradiation on transient photoluminescence measurements of GaAs and AlGaAs double heterostructures
We have performed transient photoluminescence measurements on Se doped AlGaAs and GaAs double heterostructure materials (similar to those found in advanced solar cells) as a function of radiation fluence from 1 MeV electrons for total fluences between 1/spl times/10/sup 13/ and 1/spl times/10/sup 15/ e/sup -//cm/sup 2/. We extract the effective minority carrier lifetime from the transient photoluminescence measurements and use these results to obtain lifetime damage coefficients. Carrier lifetimes in the un-irradiated samples range from a few nsec for heavily doped samples to almost 100 nsec for the more lightly doped samples. Bombardment with energetic electrons causes the carrier lifetime to decrease to values in the range of 100-200 psec. Lifetime damage coefficients are obtained for Al concentrations of 0, 10, and 20% and for Se donor concentrations between 3/spl times/10/sup 16/ and 1.5/spl times/10/sup 18/ cm/sup -3/. To our knowledge, these are the first direct measurements of lifetime damage coefficients in GaAs and AlGaAs double heterostructures. The values extracted for lifetime damage coefficients suggest: (1) greater damage than the values obtained from previous measurements using indirect techniques; (2) that the AlGaAs samples are more susceptible to reduction of carrier lifetime than are the GaAs samples; and (3) that the damage depends upon dopant concentration. We discuss the implications of these measurements for solar cell degradation in the space radiation environment.