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

In this study, we have deposited Ti, Zr, and Hf oxides on ultrathin (similar to0.5 nm) SiO2 buffer layers and have identified metastable states which give rise to large changes in their band alignments with respect to the Si substrate. This results in a potential across the interfacial SiO2 layer, significant band bending, and large shifts of the high-k valence band. The magnitude of the shift differs for the three materials and is dependant on both the SiO2 buffer layer thickness and annealing temperature. We propose a model where excess oxygen accumulates near the high-k-SiO2 interface providing electronic states, which are available to electrons that tunnel from the substrate. (C) 2004 American Institute of Physics.