Dielectric functions and electronic band states of a-Si and a-Si:H.

We have measured dielectric spectra of unhydrogenated (a-Si) and hydrogenated (a-Si:H) amorphous silicon films grown by dc magnetron sputtering deposition, using in situ spectroscopic ellipsometry. We have determined the bulk dielectric functions, using information on the film surface and bulk morphology obtained from in situ real-time ellipsometry. Compared with the a-Si film, the a-Si:H films display a decrease in the peak height of the imaginary part of the dielectric spectrum and a shift in the peak postion toward higher photon energy.We derive the density of states in both the valence band and conduction band