Ion-damaged diamond, with a point-defect density smaller than a critical density of 1022/cm3, exhibited a defect-related electrical conductivity that obeyed an Arrhenius law. After isochronal annealing, the activation energy for this conductivity increased from 0.35 to 1.15eV as the annealing temperature was increased from 200 to 1200C. A quantitative explanation this increase was based upon the fact that, when a vacancy in diamond was neutral, it had a deep localized state which was occupied by an electron

with higher-lying states. This could trap an additional electron and result in higher-lying energy levels within the band-gap. These states could form an energetically higher-lying band (the D– band) in which electrical conduction could take place. The energy gap between the Fermi level and the mobility edge of the D– band was related to the observed activation energy for conductivity. Since the shift of the Fermi level, and the width and shape of the D– band, depended upon the density of defects, the observed activation energy depended upon the defect concentration (and therefore the degree of defect annealing). This model could account for the experimentally observed variation in the activation energy for conductivity. It could also explain some of the measured large variations in activation energy reported for diamond which had been ion-implanted with dopant atoms. These had previously been interpreted as representing different energy states of the dopants, but were now attributed to unannealed residual implantation-related defects.

Model for the Defect-Related Electrical Conductivity in Ion-Damaged Diamond. E.Baskin, A.Reznik, D.Saada, J.Adler, R.Kalish: Physical Review B, 2001, 64[22], 224110 (9pp)