CHEMICAL TRENDS AND S-P HYBRIDIZATION IN THE DX CENTER IN GAAS

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. 1 8 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 (Ga(I)V(Ga)S(As))-1, has lower energy than the S-distorted broken-bond configuration (S(I)V(As))-1, and is confirmed to have the lowest energy among the negatively charged geometries. The broken-bond geometry (Ga(I)V(Ga)S(As))-1 is found to have a surprisingly (0.11 angstrom) 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.