Influence of impurities and intrinsic defects on physicomechanical properties of silicon carbide single crystals

Microindentation with a Vickers diamond pyramid was used in a study of mechanical properties of 6H-SiC with different concentrations of impurities (nitrogen and aluminium) and of intrinsic defects generated by irradiation or during growth under nonstoichiometric conditions. It was found that SiC crystals containing nonstoichiometric and radiation defects, as :yell as samples with high nitrogen concentration (C-N similar or equal to 10(20) cm(-3)), have a greater tendency for cracking, which results in deterioration of the microstrength characteristics. An analysis of the results obtained leads to the conclusion that the observed changes are primarily caused by intrinsic defect clusters rather than dislocations. (C) 1997 Elsevier Science Limited and Techna S.r.l.