Chain character of vacancy-type defects in silicon

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Abstract
With electron-nuclear double resonance the hyperfine interactions between a paramagnetic defect electron and large numbers of silicon lattice sites have been determined for a number of vacancy-related defects, viz., two charge states of the divacancy and the negative charge states of the vacancy and the oxygen-vacancy complex. In all four cases a prominent series of interactions can be distinguished that can be identified with lattice sites on a single [011]-oriented zigzag lattice chain that emanates on both sides from the vacant lattice site(s). Additional experiments on the negative divacancy have corroborated this picture. The probability density of the electron wave function is by far most pronounced on this chain, while its decrease with distance along the chain is appreciably slower than in any other direction. In all cases about 80% of the unpaired defect electron is localized in such a chain, while within experimental uncertainty the density along the chain decreases exponentially at the same rate for all defects. A comparison with theoretical calculations of charge densities is made. The relation between this one-dimensional extended electronic structure and the so-called fifth-neighbor interaction for the diamond lattice is more firmly established.