Comparative studies of the influence of hydrogen incorporation on the electronic properties of a-Ge:H films prepared by two different techniques

We present the results of a detailed investigation of hydrogen incorporation and optical absorption in the 0.6-1.3 eV range for two series of hydrogenated amorphous germanium films (a-Ge:H) deposited by reactive sputtering (series A) and by plasma-enhanced chemical vapor deposition from germane (series B). Our results clearly show that the series samples are characterized by a larger bonded hydrogen concentration (CH), a more rapid gap variation with increasing CH, a smaller refractive index, and a lower density than [he series B samples. We also compare in ijelail the energy distribution of the localized states in the pseudo-gap and the deep-defect states density as deduced from a decomposition of the optical absorption spectra based on a theoretical model for the gap states density in amorphous tetracoordinated semiconductors.