Investigations on Nano- and Pico-Second Laser Based Annealing Combined Texturing of Amorphous Silicon Thin Films for Photovoltaic Applications

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Influence of a nano- (ns) and a pico-second (ps) laser pulse in annealing and texturing of amorphous-silicon (a-Si) films on crystalline silicon substrates by pulsed Nd<SUP>3+</SUP>:YAG lasers is investigated. In theoretical studies, the thermal model was considered for the ns-laser annealing and the plasma model with an appropriate energy relaxation time was used for the ps-laser annealing, as both the processes are different on a time-scale. Crystallization depth was estimated at different wavelengths, and interface temperature between a-Si films and c-Si substrates was compared. Modeling results shows that with a ns-laser annealing at longer wavelength (1064 nm) has a weak absorption and therefore higher laser fluence is required to raise the film temperature to a required level and it was in agreement with the experimental results. Also the estimated heat diffusion region at the a-Si/substrate interface was significant due to the ns-order pulse-width. Whereas, in the case of a ps-laser (1064 nm), it was possible to anneal the a-Si film with a lower laser fluence. In addition, the estimated heat diffusion length at the a-Si film/substrate interface was lower than the ns-laser assisted treatment.