Influence of Laser Beam Profile on Nd3+:YAG Laser Assisted Formation of Polycrystalline-Si Films in Underwater Conditions

Influence of the Gaussian, flat-top and line beam profiles of the second harmonic pulsed Nd3+:YAG laser on the formation of a polycrystalline-silicon (poly-Si) on a-Si thin film in water ambience was investigated. Amorphous silicon (a-Si) thin films with thickness of 1000 nm and 400 nm deposited on crystalline Si (c-Si) substrates were treated with different laser-fluence values under water. In order to induce texturing of surface along with annealing, laser beam overlap technique with different percentages of spot overlap was used. The fluence window for crystallization was experimentally analyzed through in-situ reflectivity measurements. Surface morphology, crystalline characteristics and electrical characteristics were studied to confirm the extent of crystallization. The percentage of improvement in the crystallinity was estimated based on the suppression of the a-Si broad band in the XRD analysis. It was estimated to be 82% corresponding to the laser fluence ranging from approximate to 260mJ/cm(2) to 450 mJ/cm(2) for 50% of spot overlap. The crystalline characteristics of the film obtained with the Gaussian, line and the flat-top beam profiles were comparable for higher percentage of overlapping. However, uniform distribution of the texture height was obtained with the flat-top and the line beam profiles. Results obtained with under-water treatment showed improvement compared to that in the air.