Investigations of the electron transport behavior in microcrystalline Si films

Fully crystallized dense μc-Si:H films with no trace of amorphous silicon have been obtained on glass substrates by standard rf glow discharge plasma CVD technique using a mixture of SiF4, Ar and H2 at 200 °C. Temperature dependence of the dark conductivity (σd) has been measured from 20 to 440 K on samples having different thicknesses. Above room temperature (300–440 K), the carrier transport is found to be thermally activated with a single activation energy. At low temperature (300–80 K) the thicker films (>500 nm) show tunneling of carriers through barriers similar to what is observed in granular metals. Thinner samples exhibit a continuous bending in the σd at low temperatures that has been explained in terms of the Meyer–Neldel rule. Results can be understood in terms of an increased degree of disorder in thinner samples.