Effect of spatial defect distribution on the electrical behavior of prominent vacancy point defects in swift-ion implanted Si

This is the authors' abstract. We don't add key points for this paper.

Samples of epitaxially grown n-type silicon have been implanted at room temperature with low doses (10⁶--10⁹ cm^-2) of He, C, Si, and I ions using energies from 2.75 to 46 MeV. Deep level transient spectroscopy studies reveal that the generation of divacancy (V₂) and vacancy-oxygen (VO) pairs has a distinct ion mass dependence. Especially, the doubly negative charge state of the divacancy, V₂(=/-), decreases in intensity with increasing ion mass compared to that of the singly negative charge state of the divacancy, V₂(-/0). In addition, the measurements show 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 demonstrate 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 occurs with annealing. Concurrently, the strength of the V₂(-/0) level decreases in a wide temperature range starting from below 200 ^∘C, accompanied by an increase in the amplitudes of both the VO and V₂(=/-) peaks. In order to account for these results a model is introduced where local carrier compensation is a key feature and where two modes of V₂ are 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 is 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 is 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 remains constant (~1.2 vacancies/ion/) irrespective of the type of ion used, which provides strong evidence for the validity of the model. Annealing at temperatures above ~300 ^∘C is found to reduce the spatial localization of the defects and migration of V₂ occurs with subsequent trapping by interstitial oxygen atoms and formation of divacancy-oxygen pairs.