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

Fast transient methods have been used to determine the electron drift mobility μe and lifetime τe 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, μe τe ≃ μh, τh and both are proportional to d2. It is shown that the thickness dependence of μe τh arises almost entirely from that of τe. For d≳ 10 μm, τe 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 μe τe is given.