ELECTRONIC TRANSPORT IN THERMALLY CRYSTALLIZED SIC FILMS ON SAPPHIRE

Fine-grained (d approximate to 0.1 mu m), polycrystalline (pc) SiC films were prepared on top of insulating and optically transparent sapphire substrates by a thermal crystallization technique (SiCOS films). Unlike high-temperature deposited pc-SiC films, SiCOS films exhibit a very low d.c. conductivity in the dark (sigma approximate to 10(-8) Ohm(-1) cm(-1)) and an efficient photoconductivity on illumination with short-wavelength UV light. Relatively high n- or p-type conductivities (sigma approximate to 1 Ohm(-1) cm(-1)) were obtained after implantation of N, P and Al ions. It is argued that the electronic transport in the thermally crystallized films is limited by a grain-boundary-dominated conduction process in which thermal activation across potential barriers competes with tunnelling through these same barriers.