Raman spectra of intrinsic and doped hydrogenated nanocrystalline silicon films

Abstract

Raman scattering characteristics of intrinsic and doped hydrogenated nanocrystalline silicon films which prepared by a plasma-enhanced chemical vapor deposition system are investigated. Results indicate that Raman spectra depend intensively on microstructure and impurity in the films. Taking into account phonon confinement effect and tensile strain effect in Si nanocrystals, peak redshift of measured transverse optical modes in Raman spectra of intrinsic films can be well interpreted. With respect to Raman scattering from doped samples, besides phonon confinement effect, the peak of experimental transverse optical mode further downshifts with heightening doping level, which can be primarily assigned to impurity effect from doping. In addition, the increase in relative integral intensity ratio of transverse acoustic branch to transverse optical mode and that of longitudinal acoustic branch to transverse optical mode with decreasing mean dimension of nanocrystals and heightening doping ratio, respectively, can be ascribed to disorder. Furthermore, at the same doping level, incorporation of boron can induce higher disorder than incorporation of phosphorus in nc-Si:H films.