Influence of oxygen vacancies on the electronic structure ofHfO2films

Abstract

We investigated the unoccupied part of the electronic structure of the oxygen-deficient hafnium oxide $(\mathrm{Hf}{\mathrm{O}}_{\ensuremath{\sim}1.8})$ using soft x-ray absorption spectroscopy at O $K$ and Hf ${N}_{3}$ edges. Band-tail states beneath the unoccupied Hf $5d$ band are observed in the O $K$-edge spectra. Combined with ultraviolet photoemission spectrum, this indicates the non-negligible occupation of the Hf $5d$ state. However, Hf ${N}_{3}$-edge magnetic circular dichroism spectrum reveals the absence of a long-range ferromagnetic spin order in the oxide. Thus, the small amount of $d$ electron gained by the vacancy formation does not show intersite correlation, contrary to a recent paper [M. Venkatesan et al., Nature 430, 630 (2004)].