Structure and electronic states in a-Si:H thin films

The hydrogenated amorphous silicon (a-Si:H) thin films were prepared by plasma enhanced chemical vapor deposition at various substrate temperatures. This paper examined the relationship between structural evolution and electronic states of the tested thin films. Raman spectroscopy was used to evaluate the structural evolution in amorphous network. Meanwhile, Fourier transform infrared spectroscopy was applied to explore the change of hydrogen in thin films. Results show that the order of network on short and intermediate scales, the content and bonding mode of bonded hydrogen, as well as the intrinsic stress and silicon coordination defects, and closed rings in the thin films, vary with the deposition temperature. The dielectric spectra of samples were measured using SE850 spectra ellipsometer. The density of electronic band states (DOS) in both valence band and conduction band for a-Si:H thin films was obtained by fitting the measured dielectric spectra. The results, verified by optical measurement, reveal that the effect of hydrogenation on band edge DOS is predominant in comparison with that of network relaxation.