The O vacancies introduced by the homo-epitaxial growth of thin films on titanate substrates were studied by means of positron annihilation. The films were grown by molecular-beam epitaxy, without using an oxidant. The Doppler broadening spectra of the annihilation radiation were measured as a function of the incident positron energy for SrTiO3/SrTiO3 samples fabricated under various growth conditions. The line-shape parameter corresponding to the annihilation of positrons in the substrate was found to be increased by the growth of the film. This increase was attributed to the diffusion of O from the substrate into the film, and the resultant introduction of O vacancies into the substrate. Two different types of defect in the substrate were identified: one was an O multivacancy, such as O divacancies. The other was a complex with Sr vacancies. The concentration of O vacancies in the sub-surface region increased as the substrate temperature during growth decreased below 320C. This was attributed to the decrease in the diffusion length of O at low temperatures, and the resultant accumulation of O vacancies in the sub-surface region.

Study of Oxygen Vacancies in SrTiO3 by Positron Annihilation. A.Uedono, K.Shimayama, M.Kiyohara, Z.Q.Chen, K.Yamabe: Journal of Applied Physics, 2002, 92[5], 2697-702