Absorption Strengths of Si-H Vibrational Modes in Hydrogenated Silicon

Abstract

ABSTRACTInfrared absorption data of various Si:H samples involving several series of a-Si:H films as well as µc-Si:H and c-Si:H samples were analyzed to obtain ratios of the absorption strengths A of the Si-H stretching modes at 2000 and 2100 cm−1 and of the Si-H wagging mode at 640 cm−1. Hydrogen effusion measurements were used to obtain the absolute values of A. The results suggest essentially equal absorption strengths for the two Si-H stretching modes and a ratio of wagging and stretching absorption strengths independent of hydrogen density NH. Films with predominant 2100 cm−1stretching absorption show a stronger sample dependence of A than observed for samples with predominant 2000 cm−1absorption. A slight increase of the absorption strength of the Si-H wagging and stretching modes with rising hydrogen concentration is observed for a-Si:H films and is attributed to the decrease of the refractive index. Enhanced A values of µc-Si:H samples compared to a-Si:H samples point to the presence of molecular hydrogen.