Internal photoemission at interfaces of high-κ insulators with semiconductors and metals

Abstract

Internal photoemission spectroscopy provides the most straightforward way to characterize the relative energies of electron states at interfaces of insulators with metals and semiconductors by measuring the spectral onset of electron/hole photoemission from one solid into another. The article reviews the application of this technique for characterization of advanced nanometer-thin insulators prospected to be used in microelectronic devices. Fundamental aspects and technical features of the internal photoemission experiments are discussed together with basic electronic properties of a number of investigated high-permittivity insulating films and their interfaces in semiconductor heterostructures. Significant differences are found in the electronic properties of nanometer-thin amorphous insulating layers as compared to the known bulk phase characteristics. The band alignment at the interfaces of these insulators with metals is found to be highly sensitive to the surface preparation procedures. By contrast, at semiconductor/oxide interfaces the parameters of occurring interlayers affect the energy barriers only marginally at least in the case of studied oxides with close bandgap width $(5.6–5.9\mathrm{eV})$ . The latter finding is in favor of the models describing the band offsets at semiconductor/insulator interfaces on the basis of the bulk density of electron states. Deviation of metal/oxide interfaces from this simple behavior is explained by (unintentional) formation of a polarization layer at the interface which may contain uncompensated charges and dipoles affecting the barrier height.