Hole dangling-bond capture cross-sections in a-Si:H

It is demonstrated that the occupation statistics for a Gaussian distribution of dangling bond states may account for the measured variation of hole mobility-lifetime values in hydrogenated amorphous silicon as the Fermi energy is systematically varied by doping from about 0.55 eV to 1.05 eV below the conduction band edge. An assessment of how the deduced dangling bond parameters may be influenced by underlying doping effects suggests that the minimum cross-section ratio for hole capture into charged (sh-) and neutral (sh0) dangling bond states requires that sh-/sh0 = 5. The capture of holes is consequently dominated by charged dangling bonds provided the Fermi energy lies within the upper half of the band-gap. Both sh- and sh0 are observed to depend upon temperature (T) as sh ? T-ß which may indicate the presence of tunnelling transitions between valence band tail states and dangling bonds.