The Sn- and S-related DX centers in GaAs are studied from first-principles calculations based on supercell models within the local-density approximation. The calculated emission barrier for the Sn-related DX center with the broken-bond configuration is lower by 0.18 eV than that in Si, in good agreement with the observed value (0.16 eV) from the deep-level transient spectroscopy. This considerably low emission barrier in the Sn-related DX center is attributed to weak s-p hybridization of the Sn dangling bond in the broken-bond configuration. In the case of S, the first-neighbor Ga distorted broken-bond configuration (GaI{V}GaSAs{)}^{{{-}}1}$ has lower energy than the S-distorted broken-bond configuration (${S}IVAs{)}^{{{-}}1}$, and is confirmed to have the lowest energy among the negatively charged geometries. The broken-bond geometry (${Ga}IVGa{S}As)^-1 is found to have a surprisingly (0.11 {}) shorter Ga-S bond length than the shallow center. This prominent feature of GaAs:S provides important insight for the explanation of results of an extended x-ray-absorption fine-structure measurement. Finally, we reveal that the chemical trend in the stability of the broken-bond geometries of the DX center is closely related to the degree of the s-p hybridization inherent to the distorted atom.
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Saito et al. (1993) studied this question.