Dependence of Micro-Raman Spectra on Hydrogenation in Nanocrystalline Silicon

Abstract

Nanocrystals in a variety of hydrogenated nanocrystalline silicon films noticeably undergo a light-induced change. Micro-Raman spectra were measured for different levels of laser excitation to observe not only the nanocrystallization but also the temperature change and structural disordering in nanocrystalline silicon. Depending on the rates of hydrogenation, the films exposed to a laser whose excitation levels vary from 6.4 to 64 kW/cm(2) experience the following changes: Delta omega (Raman shift) = 6.0 similar to 18 cm(-1), Delta T (temperature) = 212 degrees C, Delta omega(0) = 518 similar to 519.2 cm(-1), and alpha = 0.028 similar to 0.088 cm(-1)/degrees K, with omega(0) and alpha being disordering parameters. The measurements of light-induced change indicated that while the laser excitation led through the self-diffusion of silicon atoms to the recrystallization of amorphous networks for a lightly hydrogenated nanocrystallin silicon film, it helped mobile hydrogen atoms not only dislocate from their present sites but also relocate to their new sites in the crystal surfaces for moderately hydrogenated nanocrystalline silicon films.