The pre-exponential factor in the conductivity of undoped hydrogenated amorphous silicon

In recent papers, Mott has suggested that the pre-exponential factor σ0 in the conductivity of a-Si: H, expressed in the form σ=σ0 exp [-(E c–E F)/kT], should be σ0 = 0·03 e 2/hL i, where L i is the inelastic diffusion length. Using experimental estimates of the time between collisions he finds sigma;0 16 ω−1 cm−1. In this work the transport results derived from 70 undoped a-Si: H specimens prepared by different research groups have been examined. Taking into account the temperature dependence of both the mobility edge and the Fermi energy it is shown that experimental σ0 values agree very well with Mott's estimate.