Effects of heat treatment on the surface carrier density in p-type CdTe

The authors investigate the mechanism by which the carrier density of p-CdTe:P in solar cells decreases due to heat treatment. By successive etching of a heat-treated sample, a carrier-density profile resulting from carrier loss near the surface was found to be a real effect. Experiments with varying cadmium and phosphorous vapor pressures are presented which indicate that compensation occurs through the formation of P_Cd antisite donors. Observations of the reverse reaction by annealing a sample of p-CdTe:P with CdTe powder after first annealing in vacuum shows that it does occur but at a much slower rate than the formation of the P_Cd defects.