On the electric-dipole contribution to the valence-band offsets in semiconductor-oxide heterostructures

The continua of interface-induced gap states (IFIGS) determine the band-structure lineup at semiconductor interfaces. Hence, both barrier heights of Schottky contacts and valence-band offsets in semiconductor heterostructures are composed of a zero-charge-transfer and an electric-dipole term. The analysis of experimental barrier heights and valence-band offsets yields IFIGS branch-point energies of 3.51±0.07eV for SiO2 and 2.98±0.26eV, 2.27±0.14, and 2.87±0.14eV for the high-κ oxides Al2O3, HfO2, and ZrO2, respectively. In the oxide heterostructures, the electric-dipole terms come up to 30% of the valence-band offsets and can thus not be neglected.