Development of structural analysis method based on reverse Monte Carlo simulation and its application to catalytic chemical vapor deposition hydrogenated amorphous silicon

A method of constructing a model of three-dimensional (3D) atomic configuration is systematically studied for hydrogenated arnorphous-silicon (a-Si:H). The study is based on Reverse Monte Carlo (RMC) simulation, by which 3D atomic models can be constructed using X-ray diffraction (XRD) data. However, since the RMC models have ambiguities, the coordination number in the model is determined by infrared absorption measurement, to obtain a unique and correct final model that can satisfy various experimental results. This method is applied to the analysis of the structure of a-Si:H films prepared by catalytic chemical vapor deposition (Cat-CVD). It is confirmed that the 3D atomic model constructed by this method is correct and that it is consistent with the results obtained in other experiments such as Raman, infrared absorption (IR) and small-angle X-ray scattering (SAXS) measurements. From the 3D structure of Cat-CVD a-Si:H, the angles between two nearest neighbor Si atoms from a single silicon (Si) atom (Si-Si-Si angles) are spread widely and the root-mean-squire (rms) deviation of such a Si-Si-Si angle is about 15.7 deg and the mean Si-Si-Si angle is 107.7 deg, smaller than the tetrahedral angle of 109.5 deg in crystalline Si.