Heavily-doped 6H-type crystals were annealed in vacuum, at temperatures of about 1900C, without Si vapor. The physical properties of the as-received and annealed crystals were studied by using Hall-effect measurements, optical transmission and photoluminescence techniques. In annealed crystals, the carrier concentration was reduced by 3 orders of magnitude and the mobility was increased several-fold. It was supposed that the reduction in carrier concentration was caused partly by the diffusion of impurity atoms, from the bulk to the surface; from which they were then removed by evaporation. It was observed that the main donor level changed from about 0.1 to about 0.7eV during annealing. The origin of the new deep-donor level was unclear, but was suggested to be due to a complex which was related to the Si vacancy and N impurity.

Effect of Annealing on the Impurities of 6H-SiC Single Crystals. D.H.Shin, S.I.Vlaskina: Japanese Journal of Applied Physics - 2, 1999, 38[8A], L861-3