A diffusion model for carrier transport in a polycrystalline film

Abstract

A model for carrier transport across the grain boundary of a polycrystalline film is developed, based on a diffusion mechanism and a constant inherent mobility in the space charge region. A linear current-voltage relation is obtained, valid for small applied bias. An effective mobility is derived for the neutral crystallite-space charge composite region, which is believed to be a more accurate description of the mobility behaviour than the exp (- vb) expression. Also, a drift velocity distribution is obtained, showing a maximum at the grain boundary, but falling off rapidly away from the space charge region, in particular, at large barrier potentials. The diminishing role of the grain boundary in limiting the effective mobility as grain size increases is demonstrated. Our theory also provides a new interpretation to the low mobility as observed from Hall-conductivity measurements. © 1984.