C +-damaged diamond: electrical measurements after rapid thermal annealing to 500°C

Abstract

C +-damaged diamond layers were generated in natural type IIa diamonds by means of ion-implantation at liquid nitrogen temperature followed by rapid thermal annealing to 500°C. The resistance behaviour of these layers was then studied as a function of C +-ion dose. It was found that the postulated graphitisation threshold of 10 22 cm −3, as simulated by the TRIM computer program, could be exceeded by a large margin before such a layer became graphite when annealed at temperatures higher than 500°C. Variable range hopping conduction, ascribable to intrinsic defects, could be measured below the graphitisation threshold. The results indicate that at low doses the density of these hopping centres N( E F) relates to the wave functions (with radial extent α) of individual vacancies. At higher doses α 3 N( E F) started to decrease. This may be attributed to the formation of extended, vacancy-rich regions that act as single hopping centres. In one of the diamonds implanted, the latter process seems to have dominated up to the highest C +-CIRA ion dose of 1×10 16 cm −2 used in this study. Only at this dose did the layer become graphitic during subsequent higher temperature anneals. In the latter case, the equivalent vacancy density corresponded to ≈7×10 22 cm −3.