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 +/- 0.07 eV for SiO2 and 2.98 +/- 0.26 eV, 2.27 +/- 0.14, and 2.87 +/- 0.14 eV for the high-kappa 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. (C) 2007 American Institute of Physics.