The pre-exponential factor in the conductivity of amorphous silicon

Abstract

The pre-exponential factor σ₀ in the conductivity of a-Si:H, together with the mobility μ_ext at the mobility edge (E _c) are discussed. On the assumption (Mott 1984) that σ₀ = 0·03 e ²/hL _i, where L _i is the inelastic diffusion length, and using experimental values of the time between collisions, it is found that σ₀ = 16 Ω⁺¹ cm⁺¹ and μ_ext = 8 cm²V⁺¹ S⁺¹. Experimental values, within a factor of 2, seem consistent with this, except for the much greater value given by Silver and co-workers (1982, 1984). The hypothesis (Cohen et al. 1984) that polarons are necessarily formed at an energy above E _c is also examined.