Abstract
The influence of long-range potential fluctuations (LRPF) on the optical and electrical properties of hydrogenated amorphous silicon (a-Si:H) has been discussed for more than three decades. Traditionally, the single-electron spectrum N ( E ) of a-Si:H materials has been assumed to be determined by the short-range atomic order. In the present study, a semiempirical adiabatic model for the quantitative description of the N ( E ) dependence on the LRPF geometry is developed. Formation of morphological features such as columns or cones leads to the appearance of LRPFs as a result of the simultaneous long-range spatial confinement of all longitudinal branches of the acoustic thermal and ‘frozen-in’ phonons. The Gibbs grand canonical distribution and the local equilibrium assumption are used to describe the statistical properties of the confined disorders. Within the model, the formula derived for the single-electron spectrum reproduces both the ‘algebraic’ and exponential N ( E ) subranges observed experimentally. The parameters characterizing the simulated N ( E ) dependencies are found to be typical of ‘device-quality’ a-Si:H materials at the LRPF spatial extent of the order of 1 μm.
Published Version
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