Ion-Implantation-Induced Defects in Diamond and Their Annealing: Experiment and Simulation

The nature of damage induced by ion-impact and its annealing are studied both experimentally and theoretically. The experimental methods employed include measurements of the changes in electrical conductivity, in material density and in Raman spectra. These are measured for natural type IIa diamonds containing different amounts of ion-implantation induced damage and subjected to different annealing temperatures (up to 1300 K for 20 min). The simulations performed are based on Molecular Dynamics (MD) computations using the Tersoff potential. A deeply buried highly damaged region is created inside the diamond sample by imparting high momenta to lattice atoms aimed towards the same point in the crystal. The nature of the damage so created is statistically analyzed yielding information on the formation of threefold-coordinated atoms in the damage region. The transformation that the damaged region undergoes as a result of “annealing” (up to 4000 K for 50 ps) is investigated. Both experiment and theory show that diamond which contains a low density of point defects can anneal back to diamond whereas, for damage levels beyond a certain level, it tends to graphitize. The stable defect in damaged diamond seems to be, according to both experiment and theory, the 〈100〉 split interstitial. Electrically, point defects in diamond act as donor centers.