Hydrogen-related defects in KTaO₃

Hydrogen is a ubiquitous impurity in semiconductors, in most cases sitting at interstitial sites and passivating other defects/impurities, changing their charge states. In some semiconductors, such as in wide-band-gap oxides, H can also be found in very unusual sites, such as replacing an oxygen atom (H_O), acting as a source of n-type conductivity. I.e., in these cases, H_O is a shallow donor. Directly probing the presence of H_O has been quite challenging, requiring a combination of experimental techniques. Recent experiments and calculations in SrTiO₃ indicate that H_O can also lead to long-lasting persistent photoconductivity (PPC) at room temperature, an effect that is also quite unusual since PPC is commonly only observed at low temperatures and reported to last for short periods. In this presentation, we report the results of first-principles calculations based on hybrid density functional theory for hydrogen-related defects in KTaO₃, exploring the stability of both interstitial (H_i) and the substitutional H_O configurations, and their interactions with other defects, especially the Ta and K vacancies. We also discuss the effects of optical excitation of the defect stability and present results for the frequencies of the local vibration mode frequencies, aiming at the experimental identification of the different hydrogen impurity configurations.