Pulsed laser crystallization of a-Si:H on glass:: A comparative study of 1064 and 532 nm excitation

Amorphous silicon films of a few hundred nm thickness on glass substrates have been crystallized by pulsed Nd-YAG laser excitation of 6 to 8 ns duration at wavelengths of lambda = 532 nm and lambda = 1064 nm. The structural properties of the crystallized films obtained from Raman spectra, X-ray diffraction data and transmission electron microscopy micrographs reveal crystallites of good structural quality and several hundred nanometers in size. The best quality and size of the crystallites is obtained by complete melting of the film. For lambda = 532 nm excitation no sharp threshold for crystallization is obtained and incomplete melting of the films at low energy density leads to small crystallites and large strain in the films. For lambda = 1064 nm pulses the threshold for crystallization is very sharp due to nonlinear absorption effects and the energy density coupled into the film is very sensitive to the film thickness because of interference effects. When films, crystallized at the two wavelengths under optimized conditions are compared, the gross structural properties and crystallite sizes differ only slightly but films crystallized with lambda = 532 nm show much smoother surfaces and a larger tensile strain.