Variable-energy positron annihilation spectroscopy has been applied to the study of defects in TiO 2/p +-Si structures, in the as-grown state and after annealing in vacuum and in hydrogen, to investigate whether annealing (and film thickness) resulted in an increase of vacancy-type defects in the oxide films. It was found that the concentration of such defects remained unchanged after vacuum annealing for all films studied, but after H 2 annealing more than doubled for 150 nm-thick films, and increased by an order of magnitude for 100 nm-thick films. The nature of the vacancies was examined further by measuring high-precision annihilation lines and comparing them with a reference Si spectrum. The changes observed in the ratio spectra associated with oxygen electrons suggest that the defects are oxygen vacancies, which have been shown to enhance electroluminescence from TiO 2/p +-Si heterostructure-based devices.
Coleman, P. G., Edwardson, C. J., Zhang, A., Ma, X., Pi, X., & Yang, D. (2012). Defects in TiO 2 films on p +-Si studied by positron annihilation spectroscopy. Materials Science and Engineering : B, 177(8), 625-628. https://doi.org/10.1016/j.mseb.2012.02.023