The photo-acoustic spectra of cleaved, polished, etched and air-annealed n-type single crystals were measured at frequencies of between 30 and 312Hz. The spectra which were related to the bulk of the crystals exhibited 5 structures which were due to defects that were also present in p-type crystals. The polishing and etching, as well as the subsequent air-annealing at 100, 200 or 300C, revealed quite complex changes in the defect equilibrium in the near-surface region of the crystals. These included both changes in the relative concentration of existing defects, and the creation of new defects. The results for polished and etched crystals corresponded to the trends which were expected for etching-induced local modifications of the composition and structure, as revealed by electron spectroscopy and ion channelling. It was found that air-annealing affected all of the existing defects, and created up to 5 new defects which could not be explained in terms of a published point defect model.

A.Zegadi, M.V.Yakushev, H.Neumann, M.A.Slifkin, R.D.Tomlinson: Crystal Research and Technology, 1995, 30[4], 517-30