POSITRON BEAM STUDIES OF ARGON IRRADIATED CDS THIN-FILMS

Depth profiling studies of defects in CdS thin films using a low energ y positron beam are reported. CdS films of 1 mu m thickness on a glass substrate have been grown using the chemical bath deposition method a nd irradiated with 140 keV Ar ions to doses of 5 x 10(14) and 5 x 10(1 6) cm(-2), respectively. The Doppler broadening line shape S parameter in as-grown and irradiated films has been monitored as a function of positron beam energy E-p. S vs E-p curves have been analyzed, using a positron diffusion model in terms of annihilations at surface, epither mal and bulk states. The S parameter at the surface (S-s) is found to be significantly higher than that in the bulk. This is understood as d ue to positron trapping at a large concentration of Cd vacancies in th e surface region, which act as acceptors. The observed reduction of S- s with increasing Ar ion dose seems to indicate the formation of antis ite defects in the surface region, brought about by irradiation. At sa mple depths corresponding to the peak damage layers, the observed beha vior of the S parameter indicates that no large vacancy clusters are f ormed. Isochronal annealing studies have been carried out to investiga te the thermal stability of defects in irradiated and as-grown samples . (C) 1998 American Institute of Physics. [S0021-8979(98)05019-1].