Validity of the broken-bond model for theDXcenter in GaAs

The validity of the broken-bond model for the DX center is examined by performing supercell calculations within the local-density approximation for column-IV donors in GaAs. We confirm that the broken-bond geometry is the most stable among the atomic structures accompanied with large lattice relaxation. The calculated bond length between the dopant and the As atoms as frequency of the local vibrational model (LVM) in the broken-bond geometry agree with extended-x-ray absorption-fine-structure and Fourier-transform–infrared-absorption measurements, respectively, supporting the broken-bond model for the DX center. Furthermore we predict from the present calculation that there exists another infrared light active LVM with 274 ${\mathrm{cm}}^{\mathrm{-}1}$ in the broken-bond geometry. Detection of this mode would be clear evidence for the broken-bond model of the DX center.