Effects of Al addition on the native defects in hafnia

Abstract

Two occupied native defect bands are experimentally detected in pure HfO₂. The density of states of band one in the middle of the band gap reduces drastically with the Al addition, while that of band two slightly above the valence-band maximum remains rather unaffected. We attribute the two bands to the charged oxygen vacancy, and the oxygen-interstitial-related defect states of the HfO₂, respectively. We demonstrate that the added Al passivates the V[sub O]⁺ induced midgap states but has little effect on other aspects of the electronic structure of the material.