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

Abstract

High purity natural type Il a diamond specimens were used in this study. Conducting layers in the surfaces of these diamonds were generated using low-ion dose multiple implantation-annealing steps. The implantation energies and the ion-doses were spread evenly to intermix the point-defects, thereby increasing the probability of interstitialvacancy recombinations and promoting dopant-interstitial-vacancy combination resulting in activated dopant sites in the implanted layers. The process used to prepare our samples is known as cold-implantation-rapid-annealing (CIRA). Carbon-ion and boron-ion implantation was used to prepare the diamond specimens, and de-conductivity measurements in the temperature range of 1.5-300 K were made following each CIRA sequence. An electrical conductivity crossover from the Mott variable range hopping (VRH) to the Efros-Shklovskii VRH conduction was observed when the temperature of insulating samples was lowered. The conductivity crossover temperature Tcross decreases with increasing concentration of the boron-ion dose in the implanted layers, indicating the narrowing of the Coulomb gap in the single-particle density of states near the Fermi energy. (Abbreviation abstract)