Underwater annealing and texturing for enhancing electrical characteristics of n-aSi/p-cSi using Nd³⁺:YAG laser beam-overlap technique with a wavelength of 532 nm

The influence of the laser beam profile on simultaneous wide-area crystallization and texturing of amorphous silicon (a-Si) thin films in water ambience is investigated by using a pulsed laser-beam-overlap technique. A Q-switched Nd3+:YAG laser with the second harmonic wavelength of 532 nm and different beam profiles, namely Gaussian and flat-top, was used for the annealing of 1-μm thick a-Si films deposited on crystalline silicon (c-Si) substrates. High density and smaller-sized conical spikes with an increase in grain size of around 25% and improved photoconductivity characteristics (9% to 17%) were observed after laser treatment was carried out in water when compared with that in air. Further, crystalline characteristics were also improved with the flat-top beam profile as compared with that of the Gaussian beam profile. The necessary laser fluence range based on the thermal modeling in the underwater ambience is in good agreement with the experimentally measured values between 150 and 600 mJ/cm2. The improvement in morphological, crystalline, and electrical characteristics of a-Si films clearly show that underwater annealing and texturing with the Nd3+:YAG laser beam-overlap of 30% to 50% is suitable for photovoltaic applications.