Non-Arrhenius anomalous hopping electronic transport in hydrogenated amorphous silicon and composite amorphous/nanocrystalline thin films

The temperature dependence of the dark conductivity of hydrogenated amorphous silicon (a-Si:H) thin films and a-Si:H films containing germanium or silicon nanocrystalline inclusions are examined. Analysis using the reduced activation energy provides clear evidence that conduction is non-Arrhenius, and is more accurately described by an anomalous hopping expression σ (T) = σ 1 exp [- (T 0 / T) κ] where the exponent is κ ∼ 0.75 ± 0.05. This observed temperature dependence is discussed in terms of alternative models for electronic transport in amorphous semiconductors.