Transient photoconductivity in amorphous silicon

Transient photoconductivity measurements in a coplanar electrode configuration in undoped a-Si:H are explained by two decay channels. The first one, operative at excess charge carrier concentrations smaller than ${10}^{16}$ ${\mathrm{cm}}^{\mathrm{-}3}$, is ascribed to deep trapping, presumably in neutral dangling bonds. The second one, operative at higher excess charge carrier concentrations, is ascribed to electron-hole recombination where the availability of free holes controls the decay process. The transport parameters deduced from these measurements agree satisfactorily with those deduced from time-of-flight measurements. The, at first sight, paradoxical increase of transient lifetimes in material with larger densities of dangling bonds can be explained within the model presented here by an additional decay channel for free holes.