Samples of n-type material were implanted with 11B, 12C, 16O, 28Si, 74Ge, 76Ge or 120Sn ions, with energies of between 0.4 and 8.0MeV, to doses of between 107 and 1010/cm2. Because of the low doses which were used, single-collision cascades predominated and an analysis of the implanted samples via deep-level transient spectroscopy revealed 2 predominant point defects of vacancy type. These were the di-vacancy (V2) and the vacancy-O (VO) center. The generation of V2 and VO was studied in detail as a function of ion mass, dose, dose-rate, sample depth and sample temperature. It was found that the surface-enhanced annihilation of migrating defects played a large role in depleting the concentrations of V2 and VO centers near to the surface. The concentrations of V2 and VO increased linearly with ion dose, but the generation efficiency per incoming ion decreased at high dose rates after exhibiting a constant value below 108/cm2s. This dose-rate effect exhibited a dependence upon ion mass, and was qualitatively predicted by computer simulations of defect reaction kinetics; involving a model in which the interaction between individual collision cascades was mainly due to rapidly diffusing Si self-interstitials. At dose-rates of less than 108/cm2s, the generation of V2 centers per ion-induced vacancy in the damage peak region was identical, to within ±10%, for all the ion types which were used. However, the V2 centers which were formed by heavy ions were strongly perturbed; as reflected by large deviations from a one-to-one relationship between the 2 deep-level transient spectroscopic peaks that were associated with the singly and doubly negative charge states of V2. There was also a broadening of the 2 peaks. In the case of VO, the numbers of these centers which were generated per ion-induced vacancy decreased with increasing ion mass. This supported the assumption that light ions were more effective in generating point defects than were heavy ions. At high implantation temperatures, a gradual relaxation of the lattice strain occurred; together with recrystallization of the disordered zones. This promoted the formation of unperturbed V2 centers and an increased generation efficiency of VO centers.

B.G.Svensson, C.Jagadish, A.Hallén, J.Lalita: Physical Review B, 1997, 55[16], 10498-507