ELECTRONIC TRANSPORT IN THERMALLY CRYSTALLIZED SIC FILMS ON SAPPHIRE

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