First principles study of the HfO2/SiO2 interface:: Application to high-k gate structures

Density functional theory simulations of HfO2/SiO2 interfaces predict the presence of midgap states associated with nonbonding Hf d electrons which result from the reduced oxygen coordination of near-interface Hf ions. These states are expected to be unoccupied in actual device structures, producing a high density of positive fixed charge during the operation of Si field effect devices containing high permittivity HfO2 dielectrics. Our results further demonstrate how the segregation of electronegative species to the HfO2/SiO2 interface can remove gap states by accepting the nonbonding electrons. (c) 2007 American Institute of Physics.