Electron states in MOS systems (Invited)

The properties of charge carrier traps in the oxide bulk, at high-k/silicon transition regions, at the silicon interface and as dipoles are discussed from physical and electrical perspectives. In order to elucidate the charging properties of oxide traps, the statistical mechanics for occupation is derived based on a constant pressure ensemble and used to interpret the influence of negative-U states occurring in high-k oxides. For the transition region close to the silicon interface, the existence of unstable traps in the continuous shift of the energy bands between SiO2 and HfO2 is pointed out. The physical background for electrical measurements on interface states is examined and, finally, dipoles constituted by traps in high-k dielectrics for regulating threshold voltage of MOS transistors are considered