Electronic transport in thermally crystallized SiC films on sapphire

Fine-grained (d ≈ 0.1 μm), 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 (σ ≈ 10−8 Ω−1 cm−1) and an efficient photoconductivity on illumination with short-wavelength UV light. Relatively high n- or p-type conductivities (σ ≈ 1 Ω−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.