Metal-insulator transition in boron-ion implanted type IIa diamond

Electrical conductivity measurements for selected boron-ion dopant concentr ations have been made on type IIa diamond specimens in the temperature rang e 1.5-30 K. Samples have been implanted using the CIRA (cold implantation-r apid annealing) process, in which small implantation increments were used f ollowed by high-temperature annealing to achieve a significant reduction in the levels of implantation-induced radiation damage and to obtain maximum boron activation. Further post anneals at temperatures up to 1700 degrees C were carried out. Using this procedure, we have recorded, for the first ti me, metallic conductivity behaviour in implanted surface layers in single-c rystal diamond specimens with boron concentrations measured by secondary-io n mass spectrometry to be of the order of n = 10(21) cm(-3). The occurrence of a metal-insulator transition in this system is discussed. (C) 1999 Publ ished by Elsevier Science S.A. All rights reserved.