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 bo th experimentally and theoretically. The experimental methods employed incl ude measurements of the changes in electrical conductivity, in material den sity and in Raman spectra. These are measured for natural type IIa diamonds containing different amounts of ion-implantation induced damage and subjec ted to different annealing temperatures (up to 1300 K for 20 min). The simu lations performed are based on Molecular Dynamics (MD) computations using t he Tersoff potential. A deeply buried highly damaged region is created insi de the diamond sample by imparting high momenta to lattice atoms aimed towa rds the same point in the crystal. The nature of the damage so created is s tatistically analyzed yielding information on the formation of threefold-co ordinated atoms in the damage region. The transformation that the damaged r egion undergoes as a result of "annealing" (up to 4000 K for 50 ps) is inve stigated. Both experiment and theory show that diamond which contains a low density of point defects can anneal back to diamond whereas, for damage le vels beyond a certain level, it tends to graphitize. The stable defect in d amaged diamond seems to be, according to both experiment and theory, the [1 00] split interstitial. Electrically, point defects in diamond act as donor centers.