The radiation damage which was caused by ion implantation was modelled by assuming that an impinging ion left a trail of damaged spheres in its wake which consisted of conducting graphite-like material. The graphitization threshold was reached when the spheres overlapped. This conclusion was based upon a model which assumed that each ion created amorphous regions around its track. Results on Si had shown that amorphous regions nucleated only when a critical ion-dose was exceeded. Because diamond was more radiation-hard than Si, the probability of graphite-like spheres forming was considered to be low. In Si and diamond, the creation and accumulation of radiation damage during ion implantation could be explained by assuming that the primary radiation products in the collision cascades were individual vacancies and displaced atoms. In diamond, at liquid-N temperatures and moderate ion doses, these point defects became effectively frozen into the positions in which they were created. Metastable defect structures were therefore possible. By considering vacancy-interstitial interactions in diamond, it was argued that shallow donor states could be generated by quenching-in suitable atoms after ion implantation. Experiments involving O-ion implantation, followed by annealing, confirmed that O could be activated in this way so as to form donor states. These states were situated at about 0.32eV below the conduction band.

The Nature of Radiation Damage in Diamond: Activation of Oxygen Donor. J.F.Prins: Diamond and Related Materials, 2000, 9[3-6], 1275-81