Structural characterization of wavelength-dependent Raman scattering and laser-induced crystallization of silicon thin films

In this report, we present a detailed structural characterization of hydrogenated amorphous silicon (a-Si:H) and microcrystalline silicon (μc-Si:H) thin films grown using high working pressure plasma-enhanced chemical vapor deposition. It is shown that the volumetric crystalline fraction of deposited μc-Si:H thin films measured by Raman scattering differs significantly for three different excitation laser wavelengths (514.5, 632.8, and 785.0 nm) owing to differences in penetration depth due to absorption, and optical confocal depth. The results demonstrate that selection of the correct excitation wavelength for Raman experiments is a highly important factor for gaining an accurate understanding of the relationship between internal microstructures and solar cell performance. In addition, the use of a high power laser was found to induce the crystallization of a-Si:H thin films due to local sample heating during the Raman measurements, which was characterized by the appearance of a sharp peak around 500 cm− 1. It was found that both photon energy (laser wavelength) and photon flux (laser power) were important factors in inducing crystallization of the films.