The long-range ordering, electron spectrum, and properties of amorphous silicon films – II. Defect states and optical parameters

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Abstract In the first part of this article, the semi-empirical generalized Skettrup model (GSM) was presented and used to simulate the effect of a spatial extent of long-range potential fluctuations (LRPF) on the parameters of the single-electron spectrum N ( E ) of non-homogeneous amorphous silicon (a-Si:H) films. Here, the GSM is applied to the modelling of optical parameters and structural defects (dangling bonds) of such films. The spectral dependence of the optical absorption coefficient, simulated by N ( E ) convolution, was found to contain the Tauc, Urbach and ‘defect’ sub-ranges. Changes in temperature and spatial extent of the LRPF provide almost linear dependencies of the optical gap versus the Urbach tail slope in the model. Simulated parameters of the a-Si:H films prepared by both radio frequency sputtering (RFS) and glow discharge (GD) decomposition of silane showed good agreement with existing experimental data. The optical gap and Urbach tail slope energies under the GSM model were found to be typical of ‘device quality’ a-Si:H films when the LRPF spatial extent was of the order of 1 μm. Differences in the properties of a-Si and a-Si:H films, specific features of the GD and RFS a-Si:H materials, as well as the fundamental nature of the ‘hydrogen dilution’ regime were also interpreted within the framework of the GSM.