Evidence for compositional heterogeneities in hydrogenated amorphous silicon nitride films

It is found that the negative effective correlation energy (−U) model for the K defects in hydrogenated amorphous silicon nitride (a-SiNx:H) cannot explain the observed subgap absorption in the optical spectra. An alternative model which describes a-SiNx:H as a compositionally heterogeneous material with spatial band-gap fluctuations is suggested. This model allows a qualitative explanation of the experimental results without having to assume a negative sign for the defect correlation energy. Other semi-insulating amorphous semiconductors, such as a-SiOx:H, also show evidence for compositional heterogeneities.