Comparisons between intrinsic bonding defects in d0 transition metal oxide such as HfO2, and impurity atom defects in d0 complex oxides such as GdScO3

This article addresses O-atom vacancy defects in the d0 transition metal (TM) oxides HfO2 and TiO2, and Ti substitutions for Sc in the d0 complex oxide GdScO3. In each instance this results in occupied TM atoms with d1 state representations. These are important for different aspects of the ultimate scaling limits for performance and functionality in nano-scale Si devices. The occupancy of d1 states is cast in terms of many-electron theory in order to determine the effects of correlation on device performance and functionality. The first section of this article identifies equivalent d-state representations using on an ionic model for the effective valence states of Ti and Hf atoms bordering on O-atom vacancy defects. Removal of an O atom to create a neutral vacancy; this is equivalent to the bonding of two electrons to each vacancy site. This give rise to two coupled d1 states for a mono-vacancy defect. Transitions from these occupied states generate spectroscopic features in the (i) pre-edge shake-up, and (ii) virtual bound state (VBS) shake-off energy regimes in O K edge XAS spectra. The number of states confirm that these are mono-vacancy defects. The second section addresses incorporation of Ti tetravalent impurities into trivalent GdScO3, forcing Ti into a Ti3+ state and generating a d1 electronic structure. Vacancy defect concentrations in HfO2 are generally <1019 cm−3. However, the Ti solubility in GdScO3 is higher, and relative concentrations in excess of 16–17% lead to an insulator to metal transition with a ferri-magnetic electronic structure.