Defects in TiO2 films on p+-Si studied by positron annihilation spectroscopy

Abstract

► Positron spectroscopy of TiO 2 / p + Si films reveals O vacancies at 10 17 –10 18 cm −3 . ► Oxygen vacancy concentration increases with film thickness from 100 to 220 nm. ► No significant change in vacancies is seen after annealing at 500 °C in vacuum. ► After annealing at 500 °C in H the vacancies increase by up to an order of magnitude. ► The observations largely support linking O vacancies with electro-luminescence. 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.