Theory of Li- and Br-saturated vacancies in radiation damaged silicon

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Abstract
The atomic configuration, electronic states and a local vibrational mode of the Li-saturated vacancy in Si are determined using ab initio calculations. The author finds in agreement with an earlier theoretical suggestion, that this defect consists of a tetrahedral combination of a negatively charged vacancy and four positively charged Li interstitials. A C3V configuration is found to be higher in energy. This confirms recent experimental suggests that a symmetry lowering, which is found in the luminescence spectrum, is due to excitonic effects. The geometric simplicity of this defect complex suggests that it may be universal for irradiated Si doped with column I and (from chemical symmetry) column VII elements. As an example of the latter he considers the structure of the Br-saturated vacancy.