Influence of cw CO 2 -laser radiation on the amorphous-to-microcrystalline phase transition in a-Si:H films: a Raman spectroscopic study

A detailed Raman spectroscopic study of the amorphous-to-microcrystalline phase transition in hydrogenated silicon thin films on glass substrates is presented. Crystallization is induced by exposing the film surface to a continuous wave CO 2 -laser working at 10.6 μm, at constant irradiation time/variable power density and at constant power density/variable irradiation time. The induced crystallization is followed quantitatively by analyzing the Raman spectra of the exposed area. The crystallite size distribution and the film stress are then estimated using a parametric fitting procedure. The pertinent microcrystal geometry of the samples after CO 2 -laser treatment has been directly correlated to Raman spectroscopic data. Variations of several spectral features, such as bandwidths and band frequencies have been interpreted in terms of three different mechanisms including the local heating due to the CO 2 -laser heating, the reduction of crystallite size and the tensile stress of μc-Si:H films. The results are discussed in the context of recent experimental and theoretical works concerning the bond polarizability.