POTENTIAL FLUCTUATIONS IN AMORPHOUS-SILICON

Recent measurements of the electron and hole drift mobilities and the optical absorption in hydrogenated amorphous silicon have strongly supported the presence of long-range potential fluctuations (LRPF) in a-Si:H. Independently, such fluctuations were suggested as the cause of the exponential energy distribution of localized tail states in amorphous semiconductors. These two problems are analyzed theoretically, and it is shown that the experimental results on the optical absorption can, indeed, be well accounted for, even quantitatively, by the classical theory of LRPF. However, this theory does not predict a purely exponential dependence for the density of states. Such a dependence could only appear in the transition range from a Gaussian shape, which for shallow states is caused by typical classical fluctuations, to a weaker dependence caused by quantum mechanical fluctuations for deeper localization energies.