Spectroscopy of electron states at interfaces of (1 0 0)Ge with high-κ insulators

The fundamental and imperfection-related components of the electron state density at interfaces of (1 0 0)Ge with several high-κ oxides have been investigated by a set of complementary methods to reveal general trends in their evolution. Internal photoemission studies indicate that the band-derived states determining the interface band offsets and, accordingly, the carrier tunnelling rate, have similar energy band diagrams for oxides with close bandgaps (5.6–5.9 eV for HfO2, Gd2O3, La2Hf2O7) characterized by conduction and valence band offsets of 2.0 and 3.0 eV, respectively. Another studied metal oxide CeO2 was found to have an optical bandgap only slightly exceeding 3 eV and does not provide the required electrical insulation. The dominant component of the interface state spectrum is found to be associated with oxide traps. At the same time the electron spin resonance results suggest that the semiconductor surface dangling bond defects play only a marginal role in (1 0 0)Ge/high-κ oxide system which is quite dissimilar to (1 0 0)Si/oxide interfaces.