Orthorhombic symmetry DX centers in S-doped GaSb, GaAs, and AlxGa1-xAs

We identify a different type of deep donor DX center with orthorhombic C-2v symmetry in m-V semiconductors. The center is predicted to occur only for anion site dopants, especially S. Its atomic structure, obtained from ab initio calculations, is characterized by cation-cation dimer-bond formation. Experimental data on S-doped GaAs and GaSb are shown to provide support for this type of DX structure. Theoretical results for DX centers with orthorhombic and trigonal symmetries in S-, Se-, and Te-doped GaSb, GaAs, and AlxGa1-xAs alloys are examined.