Role of dangling bond charge in determining μτ products for a-Si:H

Abstract By using a model of recombination via dangling bond states, one shows that the steady-state μτ products deduced from photoconductivity and ambipolar diffusion length measurements executed on uniform a-Si:H layers, are products of the form: band mobility × recombination time . The latter are dependent on the occupation functions f + , f o , f − of dangling bond states. They are not material constants and their values differ considerably according to the specific experimental situation. The μτ products of the form band mobility × capture time are those that have a direct significance for material quality and device calculations, since f + , f o and f − do not enter into their definitions. Particulat conditions on f + , f o and f − are required so that recombination times are reduced to capture times, in other cases a connection procedure is necessary. The situation for μτ products derived from time of flight measurements is shown to be similar, except that here one has to consider the occupation functions f + , f o and f − in the dark state rather than under illumination. An illustrative example based on experimental data is given.