Crystal size and temperature measurements in nanostructured silicon using Raman spectroscopy

In this work we present a detailed structural characterization by Raman spe ctroscopy of hydrogenated amorphous silicon (alpha -Si:H) and of nanostruct ured silicon (ns-Si:H) thin films grown in radio-frequency plasma. The ns-S i:H thin films, also called polymorphous Si thin films, consist of a two-ph ase mixture of amorphous and ordered Si. The Raman spectra were measured at increasing laser intensities. Very low laser power densities (similar to1 kW/cm(2)) were used to thoroughly analyze the structure of as-deposited thi n films. Higher Raman laser powers were found to induce the crystallization of the films, which was characterized by the appearance of a sharp peak ar ound 500 cm(-1). This was attained faster in the alpha -Si:H than in the co nventional a-Si:H thin films because the silicon-ordered particles cause a heterogeneous nucleation process in which they act as seeds for crystalliza tion. The laser power densities for film crystallization, crystal size, and surface temperature were determined from this Raman analysis. The validity and application ranges of the different models that can be used to calcula te these parameters are critically discussed. (C) 2001 American Institute o f Physics.