Space-charge-limited current analysis of the leakage current and interface states of GaAs p/n diode solar cells

Abstract

GaAs p/n junction solar cells, grown by vapor transport, frequently show a change in efficiency with light concentration that exceeds the predictions of the standard model based on diffusion limited and generation/recombination current-voltage mechanisms. A cell was selected where the efficiency changed from 12 to 22% between 1 and 600 suns concentration or about four times that predicted by the standard model. The dark and light, current-voltage characteristics of this cell were modeled with a trap controlled, space-charge-limited current diode model for the device leakage current. A good fit to the experimental data required a distribution density of electron traps, in the high-resistance p/n junction interface region, on the order of 1018 cm−3 eV−1 with a minimum at 0.4 eV below the conduction-band edge. Since the measured thickness of the high resistance region is 0.1 μm, the equivalent interface state density is on the order of 1013 cm−2 eV−1 .