Crystallization of amorphous Si films for thin film solar cells

Abstract

Amorphous Si films prepared by plasma-enhanced chemical vapor deposition (PECVD) have been fully crystallized by pulsed Nd-YAG laser excitation at wavelengths of 1064 and 532 nm. Crystallite quality was observed by Raman spectroscopy showing a line width of ∼5 cm −1 at 520 cm −1. Transmission electron microscopy (TEM) micrographs show crystallite sizes of several hundred nm and crystalline reflection peaks in X-ray diffraction (XRD) are observed. The quality and size of the crystallites prepared at a wavelength of 1064 nm improved with increasing laser energy density and are most sensitive to the energy density near the threshold energy for crystallization. The optimum laser energy densities are sensitive to the film thickness due to interference effects. A comparison of crystallization at wavelengths of 1064 and 532 nm shows no difference in the crystallite quality, but at 532 nm smoother surfaces are obtained. The laser energies for crystallization at 1064 nm are higher but not as much as expected by comparison of the absorption coefficients at 1064 and 532 nm.