The mobility-lifetime products of electrons and holes, and the response time of the photocurrent and the electron drift mobility, were numerically simulated as a function of the dangling-bond density and temperature in hydrogenated amorphous material. All of the possible recombination and re-emission processes which occurred between extended and localized states were considered. It was found that the simulated results were in good agreement with experimental data. The mobility-lifetime products of holes in undoped amorphous hydrogenated material were insensitive to the dangling-bond density, at low levels of the latter, unlike the mobility-lifetime products of electrons. This asymmetrical dangling-bond density-dependence of the mobility-lifetime products of electrons and holes was attributed to an inherent asymmetry of the density-of-states distribution of the conduction- and valence-band tails. The mobility-lifetime products and the response time of the photocurrent decreased with the generation rate, whereas the electron drift mobility increased. It was noted that the effect of thermal broadening of the band-tail states had to be taken into account in simulations; especially an increase in the characteristic energy of the conduction band-tail states with temperature. As well as the defect states, the band-tail states played a very important role in the determination of the photocarrier lifetimes. In the range of low dangling-bond densities, recombination via the band-tail states predominated over that via dangling bonds, while dangling bonds became the predominant recombination centers in the range of high dangling-bond densities. The transition, from tail-state dominated to defect-state dominated recombination processes, depended essentially upon the defect density, the temperature, the generation rate, and the Fermi-level position.

F.Wang, R.Schwarz: Physical Review B, 1995, 52[20], 14586-97