Free carrier ambipolar diffusion length in amorphous semiconductors

Abstract An expression for the ambipolar diffusion length (Lamb)in amorphous semiconductors involving explicitly the densities of free carriers and their band mobilities is derived. Thus, Lamb and the photoconductivity [sgrave]photo can be related to the same set of transport parameters (band mobilities and carrier lifetimes). The formal equivalence between the expression derived here for Lamb and the one previously used in the literature (and involving drift mobilities and ‘total carrier lifetimes’) is shown. The expression derived here for Lamb served together with that for [sgrave]photo as a basis for (1) determining to what extent the characteristic electronic transport behaviour of a given film corresponds to that of a ‘truly intrinsic’ film, or not and (2) deducing a parameter μ0τ0 that characterizes intrinsic layer quality for use in p-i-n solar cells.