Role of codopant oxygen in erbium-doped silicon

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Abstract
The structural and electronic properties of Er-doped Si system with and without the codopant of oxygen are studied theoretically by using the first principle discrete variational cluster method based on the ab initio local-density approximation. Several cluster models are adopted for simulating an Er point defect located at different sites in the Si host with high symmetry. The role of oxygen is especially investigated. The results show that the presence of oxygen changes the binding energy drastically, i.e., a positive energy is needed for the incorporation of an Er defect into Si, but with the existence of surrounding oxygen atoms a negative binding energy is found. This could explain the experimental results that the presence of oxygen can enhance the effective solubility of Er in Si. The electronic structures for different Si:Er configurations with and without oxygen are calculated. Differences are found for the two cases in their density of states and charge distributions.