ELECTROCONDUCTIVITY OF AMORPHOUS-CARBON FILMS CONTAINING SILICON AND TUNGSTEN

Data on the electron transport in insulating amorphous carbon films containing silicon and tungsten atoms are presented. The films were grown by plasma-assisted chemical vapour deposition. The tungsten atoms were introduced into the growing film from the hot filament. The structure of these films consists of an atomic-scale composite of carbon and silicon random networks. The carbon network is stabilized by hydrogen and the silicon network is stabilized by oxygen. Such self-stabilized C-Si amorphous structures form an ideal matrix for the introduction of metals, in particular transition metals. These metals are distributed as separate atoms or as separate disordered networks. The addition of metal atoms allows the electrical resistivity to be changed from 10(14)-10(15) Ohm cm down to 10(-4) Ohm cm in a controlled way. Various electron transport mechanisms and percolation phenomena are observed in the diamond-like nanocomposite. It was found that in the temperature range 150-350 K the electroconductivity is of thermo-activated Pool-Frenkel nature and is characterized by two values of activation energy, 0.32 and 0.2 eV. The observed saturation of the current vs. temperature on increasing the electric field is connected with the predominance of tunnelling effects (activationless hopping conductivity and direct tunnelling at the mobility threshold). The week magnetoresistance proportional to the square of the magnetic field can be explained by the small value of localization radius at the Fermi level.