The metal-semiconductor transition in amorphous Si1-xCrxfilms-scaling behaviour and minimum metallic conductivity

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Abstract
Amorphous Si1-xCrx films with 9, ..., 19 at.% Cr were prepared by means of electron beam evaporation. The electrical conductivity was measured in the regions 2, ..., 4.2 and 14, ..., 20K. If the conductivity is smaller than sigma 0=270+or-50 Omega -1 cm-1, which corresponds to about 14 at.% Cr, its temperature dependence can be described by a scaling law, sigma (T)= sigma 0 phi (T/T0), where only T0 depends on the Cr content and preparation conditions. The asymptotic behaviour for T to 0K is given by sigma (T)= sigma 1 exp (-(T0/T)alpha ) with sigma 1=110+or-20 Omega -1 cm-1 and alpha =0.47+or-0.05. Hence, if the conductivity is smaller than sigma 0, there should be only one conduction mechanism. This mechanism is thermally activated. Thus, sigma 0 should be interpreted as the minimum metallic conductivity.