Competition between damage buildup and dynamic annealing in ion implantation into Ge

In order to investigate the effect of ion flux and irradiation temperature on defect evolution in germanium during the process of ion implantation, a focused ion beam system is used. Channeling implantation of Ga ions is performed at two very different ion fluxes (1012 and 1019 cm-2 s-1), at two temperatures (room temperature and 250 0C), and at five different fluences, ranging from 5x1012 to 5x1014 cm-2. The depth distributions of Ga and the implantation damage are determined by SIMS and micro-RBS/C, respectively. The fluence dependence of the measured range profiles and of the implantation damage is strongly influenced by the ion flux and the implantation temperature. These results are explained by the competition between damage buildup and dynamic annealing during the ion bombardment. For the two implantation temperatures considered, the time scale for intracascade defect relaxation can be estimated. At 250 °C, the maximum lifetime of the defects is less than 10 s. On the other hand, at room temperature no significant annealing is found within the first 10 s after ion impact. The measured Ga depth profiles can be reproduced by atomistic computer simulations using a phenomenological model to describe the probability that an implanted ion collides with a target atom of a damaged region. This probability depends on the total nuclear energy deposition per target atom and on two empirical parameters [1].
[1] M. Posselt, L. Bischoff, D. Grambole, F. Herrmann, Appl. Phys. Lett. 89 (2006) 151918