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

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 degreesC. 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 degreesC. 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 alpha) of individual vacancies. At higher doses alpha N-3(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 x 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 approximate to 7 x 1022 cm(-3). (C) 2001 Elsevier Science B.V. Ah rights reserved.