Effect of small crystal size and surface temperature on the Raman spectra of amorphous and nanostructured Si thin films deposited by radiofrequency plasmas

A detailed analysis by Raman spectroscopy of amorphous and nanostructured silicon (Si) thin films deposited by PECVD is presented. The nanostructured Si films, also referred as polymorphous Si. were obtained under plasma conditions where Si nanoparticles and radicals contributed to the film growth. Such films consist of nanometric ordered domains embedded in an amorphous matrix, as demonstrated by TEM [1]. However, these films seem to be non-structured by Raman spectroscopy analysis, as revealed from the spectra performed at very low laser power density (similar to 1 kW/cm(2)). where structural modifications are sure to be not induced. Higher laser powers are found to produce the film crystallization. From these Raman spectra, the surface temperature reached by the sample during laser irradiation, Si-crystallite size and crystalline volume fraction can be determined. Nevertheless, care is needed to well quantify the Raman spectra, because both crystal size and surface temperature affect the crystalline Raman peak in different extent. In this study, a method to quantify the Raman spectra is proposed. The most conventional models for calculations are critically reviewed. (C) 2002 Elsevier Science B.V. All rights reserved.