Morphology, Phonon Confinement and Properties of a-Si:H Films

Abstract

ABSTRACTIt is usually assumed that optical and electrical properties of amorphous semiconductors are determined by the short-range-order (SRO) parameters of atomic structure. The SRO parameters behavior is considered here as governed by morphology geometrical parameters (MGP) variations. Generalized Skettrup model is developed for a quantitative description of the MGP influence on the density of electron states distribution N(E). Common N(E) relation for the power, exponential and the ‘defect’ regions of the dependence is derived both for adiabatic (optical) and non-adiabatic (thermal) electron excitation processes. The simulated (by the N(E) convolution) spectral dependence of the opti-cal absorption coefficient contains the Tauc, Urbach and the ‘defect’ parts. The optical gap and the Urbach tail slope energies are typical for the ‘device quality’ a-Si:H films at the average morphology geometrical parameters values of order of 1 μm. Nearly linear the optical gap versus the Urbach tail slope energies dependence is obtained at the mor-phology geometrical parameters and temperature changes. Good agreement of experi-mental and the simulation results is achieved for a-Si:H films, prepared both by the RF sputtering and by the silane decomposition.