Isochronal annealing and the thermal evolution of electron- and proton-induced defects in semi-insulating 4H-polytype samples were investigated by using positron annihilation techniques. Positron lifetime and Doppler-broadening measurements were used to investigate the thermal stability of the radiation-induced defects, as well as possible clustering mechanisms during isochronal annealing. The as-grown samples contained vacancy-type defects which exhibited a positron lifetime of about 248ps; yielding a mean lifetime of 142ps. The observed lifetimes suggested the presence of complexes having a divacancy nature. The concentrations of these defects were of the order of 3 x 1016/m3. A value of 138ps was found for the bulk lifetime. The mean lifetime exhibited an increasing dependence upon the radiation dose. The grown-in defects were found to be stable even at 1600C. The annealing behaviour of irradiated semi-insulating samples was quite different to that observed in n- or p-type samples.

Microstructural Evolution of Radiation-Induced Defects in Semi-Insulating SiC During Isochronal Annealing. W.Puff, A.G.Balogh, P.Mascher: Materials Science Forum, 2000, 338-342, 965-8