Influence of oxygen vacancies on the electronic structure of HfO2 films

We investigated the unoccupied part of the electronic structure of the oxygen-deficient hafnium oxide (HfO similar to 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 , Nature 430, 630 (2004)].