AN INVESTIGATION OF POINT-DEFECTS IN SILICON-CARBIDE

Positron lifetime measurements on bulk samples of single crystal SiC w afers have shown that both 6H and 4H polytypes exhibit a bulk lifetime of 150 +/- 2 ps. All samples contained a second, defect-related lifet ime component, ranging in value from 250 to about 300 ps with rather l ow intensities. The defect structure exhibited by the nanocrystalline samples is, not unexpectedly, much more complex. Positron beam experim ents on Electron Cyclotron Resonance Chemical Vapour Deposited (ECR-CV D) SiC thin films showed that the positrons are very sensitive to chan ges in important film parameters as a function of the deposition condi tions. It was found that the film density is lower than expected, prob ably due to hydrogen incorporation; variations in composition among di fferent films were detected through variations in the S parameters, an d differences were observed in the electric field at the film-substrat e interface due to hydrogen passivation of dangling bonds and differen t substrate resistivities.