On the preparation of vanadium-doped semi-insulating SiC bulk crystals

Vanadium doped and B/V codoped 6H-SiC bulk crystals were grown under high purity conditions to obtain SiC with semi-insulating properties. The incorporation of V and donor/acceptor impurities and the resulting impact on electrical behavior was studied. In nominally undoped crystals, the nitrogen concentration decreases exponentially with growth time. For boron doping, the B concentration roughly remains constant during growth. Adding V directly to the starting SiC material, the dopant source depletes completely during growth. This can be avoided by lowering the growth temperature to decrease partial pressure. For vanadium compensating nitrogen impurities, trap activation energies of 700... 850 meV were obtained. V-related peaks are observed in near infrared absorption spectra. Specific resistivities at room temperature range from 2 x 10(10) Omegacm up to about 6 x 10(11) Omegacm, while resistivity mappings reveal imhomogeneities. As vanadium compensates boron in B/V codoped crystals, trap activation energies of 1.3... 1.6 eV were found in the main parts of the bulk crystals.