Band alignment at the interfaces of Al2O3 and ZrO2-based insulators with metals and Si

Abstract

Internal photoemission of electrons was used to determine the band alignment in metal (Mg, Al, Ni, Cu, Au)-oxide-silicon structures with Al2O3- and ZrO2-based insulators. For Al2O3- and ZrO2 layers grown on Si by atomic layer deposition the barrier height between the Si valence band and the oxide conduction band was found to be 3.25 and 3.1 eV, respectively. Thermal oxidation of the Si/oxide stacks results in a barrier height increase to ≈4 eV for both cases due to formation of a silicate interlayer. However, there is a significant sub-threshold electron emission both from silicon and metals, indicating a high density of states in the band gap of the insulators. These states largely determine the electron transport across metal oxides and may also account for a significant dipole component of the potential barrier at the metal/ZrO2 and metal/Al2O3 interfaces.