The thickness dependence of excess carrier lifetime and mobility in amorphous silicon junctions

Abstract

Fast transient methods have been used to determine the electron drift mobility μ_e and lifetime τ_e in a-Si p-i-n junctions ranging in thickness from d ≃ 0·4 to 15 μm Similar data were obtained for holes on the thinner specimens. For d <4 μm, μ_e τ_e ≃ μ_h, τ_h and both are proportional to d². It is shown that the thickness dependence of μ_e τ_h arises almost entirely from that of τ_e. For d≳ 10 μm, τ_e tends towards a constant value of 1–2 μs, which represents the true electron lifetime of the material with respect to deep centres. The free lifetime is about 100ns. A possible explanation for the observed thickness dependence of μ_e τ_e is given.