Dipole formation and band alignment at the Si(111)/CuInS2 heterojunction

Heterojunctions between Si(111):H faces and molecular beam epitaxy grown CuInS2 thin films were investigated. The interface formation was studied by means of photoelectron spectroscopy and low energy electron diffraction. Initial sulfur exposure of the Si substrate at 750 K leads to a surface dipole of (0.61±0.10) eV. Upon subsequent CuInS2 deposition, an interface dipole of (1.0±0.2) eV is observed. The valence band offsets between Si and CuInS2 films of different [Cu]/[In] ratios were determined and an average valence band offset of (0.08±0.15) eV is obtained. Comparison with model considerations points out that the experimental values of the valence band offset are consistent with the observed interface dipole.