Process-dependent band structure changes of transition-metal (Ti,Zr,Hf) oxides on Si (100)

The Ti, Zr and Hf oxides were deposited on ultrathin (∼0.5 nm) SiO ₂ buffer layers. The metastable states which give rise to large changes in the band alignments of these oxides with respect to the Si substrate were identified. It was shown that the magnitude of the shift of high-k valence band differs for the three materials and is dependent on both the SiO ₂ buffer layer thickness and annealing temperature. A model was proposed where excess oxygen accumulates near the high-k-SiO ₂ interface providing electronic states, which are available to electrons that tunnel from the substrate.