TEMPERATURE-DEPENDENT RAMAN STUDIES OF HYDROGENATED-AMORPHOUS-SILICON FILMS

We report here the temperature-dependent Raman-scattering studies of the hydrogenated amorphous silicon (a-Si:H) films in the range 77-623 K. The bandwidth (GAMMA) of the optic phonon obtained from the measured Raman spectra was found to have a nonlinear behavior when plotted versus the temperature and displayed a minimum magnitude (GAMMA(min)) when the Raman-measurement temperature equaled the deposition temperature. Furthermore, the GAMMA(min) was found to be nearly independent of the H concentration. These results are therefore attributed to the postdeposition effect of an extrinsic stress that originates from the difference in thermal expansion of the film and substrate. The extrinsic stress is proposed to induce additional density of weak bonds, which may enhance the degradation of optoelectronic properties of a-Si:H. Furthermore, if the extrinsic stress effects are eliminated, the minimum width of the bond-angle deviation is expected to reduce to approximately +/-6.