FREE-CARRIER AMBIPOLAR DIFFUSION LENGTH IN AMORPHOUS-SEMICONDUCTORS

An expression for the ambipolar diffusion length (L-amb) in amorphous semiconductors involving explicitly the densities of free carriers and their band mobilities is derived. Thus, L-amb and the photoconductivi ty sigma(photo) can be related to the same set of transport parameters (band mobilities and carrier lifetimes). The formal equivalence betwe en the expression derived here for L-amb and the one previously used i n the literature (and involving drift mobilities and 'total carrier li fetimes') is shown. The expression derived here for L-amb served toget her with that for sigma(photo) as a basis for (1) determining to what extent the characteristic electronic transport behaviour of a given fi lm corresponds to that of a 'truly intrinsic' film, or not and (2) ded ucing a parameter mu(0) tau(0) that characterizes intrinsic layer qual ity for use in p-i-n solar cells.