Effect of heat treatment on electron traps in n-type GaAs

Annealing of bulk and vapor phase epitaxial (VPE) n-type GaAs at about 600°C for one hour in an apparatus of fused quartz (GE 204 or vitrosil) is seen to cause considerable reduction in the free electron concentration (N_S) and the commonly observed 0.85 eV electron traps (N_T) in these materials. Heating at elevated temperatures in the same environment causes an n-type sample to convert to p-type. The reduction in N_S and N_T is found to be considerably smaller for comparable heat treatments in a vacuum system free from quartz. It is suggested that the observed reduction is caused by in-diffusion of impurities like Cu and Li which are present in the types of quartz used in the experiments.