Effect of hydrogen concentration on structure and photoelectric properties of a-Si:H films modified by femtosecond laser pulses

Abstract

The crystallization of hydrogenated amorphous silicon films with femtosecond laser pulses is one of the promising ways to produce nanocrystalline silicon for photovoltaics. The structure of laser treated films and their hydrogen content are the most important factors for determining the photoelectric properties of materials. In this work we investigated the effect of femtosecond laser irradiation of a-Si:H films with different fluences on crystalline volume fraction, hydrogen concentration, and photoelectric properties of this material. Our results point out that hydrogen out-diffusion accompanies the crystallization process. The increase of hydrogen concentration in the initial a-Si:H films structure affects the kinetics of the crystallization process, but does not lead to a substantial increase of hydrogen concentration remaining in the film after the treatment. The deficiency of hydrogen in the films’ structure results in degradation of their photoconductivity, thus other strategies of a-Si:H laser crystallization or postprocessing should be found to obtain device-quality films using ultrafast laser processing.