Heavily-doped 6H-type crystals were annealed in vacuum at temperatures near to 1900C, without Si vapour. The physical properties of the as-received and annealed crystals were studied by means of 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 suggested that the reduction in carrier concentration was caused partly by the diffusion of impurity atoms from the bulk to the surface; from whence they were then removed by evaporation. The main donor level changed from 0.1 to 0.7eV during annealing. The origin of the new deep donor level was unclear, but was suggested to be due to a complex which involved a 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