Effect of gap-state parameters in intrinsic a-Si:H

The effect of various gap-state parameters in a thin layer of a-Si:H in thermodynamic equilibrium has been investigated computationally. Gap states considered are conduction- and valence band tail state, and donor- and acceptor-like dangling-bonds. The tail-state slopes, and dangling-bond amplitudes, energies and distribution widths are the parameters that have been varied, with reference to a set of symmetrical parameters that give truly intrinsic a-Si:H. For these various parameter values we calculate the position of the Fermi level in the gap (for the truly intrinsic layer the Fermi level is precisely at midgap). We find that variations in all of the parameters are capable of inducing either an n-type or a p-type character in the a-Si:H. Variations in the dangling-bond energies and amplitudes have a particularly significant effect, whereas variations in tail-state slopes have only a slight effect.