Electronic Conduction in Silicon Carbide

Pure silicon carbide was prepared by decomposition of the vapors of silicon tetrachloride and toluene on a hot carbon filament. Various n- and p-type impurity atoms were introduced by the addition of volatile metallic chlorides during the preparation. For the pure substance either n- or p-type crystals could be obtained by varying the ratio of the reaction constituents. The results show that semiconductivity in silicon carbide may be due either to nonstoichiometric proportions of silicon and carbon, or to the presence of impurity atoms, or (as probably occurs in the commercial product) to both circumstances simultaneously. A theoretical model for electronic conduction in silicon carbide is proposed, which satisfactorily explains the magnitude of the low and high temperature activation energies observed, their different ratios in n- and p-type crystals, the occurrence of conduction at one of the disturbance energy levels, and the anomalous low Hall constant at low temperatures found in black but not in green silicon carbide. The model may be applicable to other semiconductors in which disturbance centers can give rise to electrons in unlocalized excited states.