Schottky barrier formation in liquid-phase-sintered silicon carbide

Liquid-phase-sintered SiC materials, all doped with 3 vol.% YAG (Y3Al5O12) and sintered under identical conditions but processed in different furnaces (laboratory vs. industrial furnaces), revealed a variation in electrical resistivity of five orders of magnitude (10(2) vs. 10(7) Omegacm). It was expected that, due to different cooling rates, different interface structures had evolved that strongly affected electrical resistivity, i.e., changes in intergranular film chemistry and corresponding thickness. In order to verify this hypothesis, the materials were characterized employing various techniques. High-resolution transmission electron microscopy of SiC interfaces revealed an unexpected result: clean interfaces for all samples. Elemental analysis confirmed yttrium and aluminum segregation at grain boundaries. Electron holography and Fresnel-fringe imaging revealed a change in mean inner potential across SiC interfaces. It is concluded that the segregation of acceptor ions at interfaces lowers the grain-boundary Fermi energy, resulting in the formation of potential barriers (Schottky barriers) along SiC interfaces, which in turn strongly affect electrical resistivity of SiC polycrystals.