Onset of microcrystallinity in silicon thin films

Abstract

The onset of microcrystallinity in silicon thin films was realized via an amorphous-to-microcrystalline phase transition. Undoped films have been deposited by the plasma-enhanced chemical vapor deposition (PECVD) technique from silane diluted with hydrogen. Substrate temperature was set as the variable parameter in the deposition. The films were characterized by Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The presence of both amorphous and crystalline phases is indicated in the Raman spectra and the signature of grain boundary regions is not prominent for the transition films. The dominance of monohydride bonding in the amorphous matrix is revealed by FTIR spectra. TEM confirms the presence of small grains (∼50 Å) embedded in the amorphous matrix for the films prepared at the transition region. At the onset of crystallinity, films have a higher order of dark conductivity than a typical amorphous film, but are still photosensitive. Better stability under illumination is observed compared to amorphous silicon.