Difference in space-charge recombination of proton and electron irradiated GaAs solar cells

GaAs component cells, representative of the middle cell in Ga _0.5 In _0.5 P/GaAs/Ge triple junction solar cells, were irradiated with protons and electrons of various energies and fluences. The local ideality factor, calculated from the measured dark J-V curves, exhibits a characteristic signature of the irradiating particle. With the help of an analytical model based on Shockley-Read-Hall statistics, the recombination current in the space-charge region is calculated, and the local diode ideality factor is reproduced accurately. The inclusion of defect levels away from the intrinsic Fermi level in the bandgap is found to be essential, since a classical two-diode model fails to describe the experimental data. On the basis of literature data of known defect levels in irradiated GaAs, the associated lifetimes and defect introduction rates are derived.