Similarities between amorphous and microcrystalline forms of hydrogenated silicon from periodic DFT modelling: coupled Si–H vibrations in (SiH)X groups, X = 2–4

Abstract

ABSTRACTMicrostructure factor (MF) is one of the most important properties of hydrogenated silicon (HS) used in industry. It is expressed via vibrational intensities of low stretching modes (LSM) of Si–H and high stretching modes (HSM) of SiH2/SiH3 bonds, i.e. MF = IHSM/(ILSM + IHSM). Mixed character of HSM due to Si–H contributions (together with SiH2/SiH3 ones) is confirmed by vibrational analysis of Si–H valence bonds in a 120Si:18H model of amorphous HS at the Perdew-Burke-Ernzerhof (PBE)/projector augmented wave (PAW)level. Comparison with precedent solutions for di- and poly-vacancies in microcrystalline HS shows that the redistribution of its Si–H modes between HSM and LSM bands depends on the extent of perturbation of the vacancies. This relation between the HSM/LSM repartition and HS distortion explains possible MF dependence from short or medium range ordering and its link with crystallisation kinetics.