Samples of epitaxially grown n-type silicon were implanted at room temperature with low doses (106–109/cm2) of He, C, Si and I ions using energies from 2.75 to 46MeV. Deep level transient spectroscopy studies revealed that the generation of divacancy (V2) and vacancy-oxygen (VO) pairs had a distinct ion mass dependence. Especially, the doubly negative charge state of the divacancy, V2(=/−), decreased in intensity with increasing ion mass compared to that of the singly negative charge state of the divacancy, V2(−/0). In addition, the measurements showed also a decrease in the intensity of the level assigned to VO compared to that of V2(−/0) with increasing ion mass. Carrier capture cross-section measurements demonstrated a reduction in the electron capture rate with increasing ion mass for all the three levels V2(−/0), V2(=/−), and VO; but a gradual recovery occurred with annealing. Concurrently, the strength of the V2(−/0) level decreased in a wide temperature range starting from below 200C, accompanied by an increase in the amplitudes of both the VO and V2(=/−) peaks. In order to account for these results a model was introduced where local carrier compensation was a key feature and where two modes of V2 were considered: (1) V2 centers located in regions with a high defect density around the ion track (V2dense) and (2) V2 centers located in regions with a low defect density (V2dilute). The V2dense fraction does not give any contribution to the V2(=/−) signal due to local carrier compensation, and the amplitude of the V2(=/−) level was determined by the V2dilute fraction only. The spatial distributions of defects generated by single-ion impacts were simulated by Monte Carlo calculations in the binary collision approximation, and to distinguish between the regions with V2dense and V2dilute a threshold for the defect generation rate was introduced. The model was shown to give good quantitative agreement with the experimentally observed ion mass dependence for the ratio between the amplitudes of the V2(=/−) and V2(−/0) peaks. In particular, the threshold value for the defect generation rate remained constant (∼1.2vacancies/ion/Å) irrespective of the type of ion used, which provides strong evidence for the validity of the model. Annealing at above ∼300C was found to reduce the spatial localization of the defects and migration of V2 occurred with subsequent trapping by interstitial oxygen atoms and formation of divacancy-oxygen pairs.

Effect of Spatial Defect Distribution on the Electrical Behavior of Prominent Vacancy Point Defects in Swift-Ion Implanted Si. L.Vines, E.V.Monakhov, J.Jensen, A.Y.Kuznetsov, B.G.Svensson: Physical Review B, 2009, 79[7], 075206