Irradiation- or Native-Defect-Induced Gap States

Native defects can be generated in the bulk of semiconductors by irradiation with energetic particles. It was found that the Fermi levels shift to the same saturation position with increasing irradiation time, irrespective of whether the semiconductors are initially doped p- or n-type. The gap states of the irradiation-induced native defects result from the complex band structure in the same way as the interface-induced gap states. Therefore, it is not at all surprising that the irradiation-induced saturation positions of the Fermi levels agree with the calculated branch-point energies as well as the experimental values resulting from the experimental Schottky barrier heights and valence-band offsets. The conclusion of Walukiewicz that the alignment of the band-structures at semiconductor interfaces is caused by defects cannot simply be drawn from this correlation. It ultimately proved to be false, as no experimental evidence for the existence of interface-induced defects was found.