Interface-induced gap states and band-structure lineup at TiO2 heterostructures and Schottky contacts

The band-structure lineup at semiconductor interfaces is explained by the continuum of the intrinsic interface-induced gap states (IFIGS) which derive from the complex band structures of the semiconductors. Hence, the valence-band offsets of semiconductor heterostructures and the barrier heights of metal-semiconductor or Schottky contacts are composed of a zero-charge transfer and an electrostatic-dipole term, which are determined by the IFIGS's branch-point energies and the electronegativity difference of the two materials in contact, respectively. The analysis of experimental valence-band offsets at TiO2 heterostructures yields the p-type branch-point energy of TiO2 as 2.34 +/- 0.41 eV. This empirical value also explains the experimental valence-band offsets of TiO2/Si double heterostructures with SiO2, Al2O3, and Si3N4 interlayers and of metal-TiO2 Schottky contacts. The experimental valence-band offsets of Si3N4 heterostructures yield the p-type branch-point energy of this insulator as 1.53 +/- 0.11 eV.