ROLE OF DANGLING BOND CHARGE IN DETERMINING MU-TAU PRODUCTS FOR A-SI-H

By using a model of recombination via dangling bond states, one shows that the steady-state mu tau products deduced from photoconductivity a nd ambipolar diffusion length measurements, executed on uniform a-Si:H layers, are products of the form: band mobility x 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 va lues differ considerably according to the specific experimental situat ion. The mu tau products of the form band mobility x 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 defini tions. Particular conditions on f(+), f(o) and f(-) are required so th at recombination times are reduced to capture times, in other cases a connection procedure is necessary. The situation for mu tau products d erived 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 illustrativ e example based on experimental data is given.