Theory of the DX center in AlxGa1-xAs and GaAs crystals

It is argued that (1) the so-called DX center is a simple substitutional donor which is displaced from its normal, centered, lattice position, (2) its deep state is derived from a triplet of symmetry T2, not A1 as is generally assumed, and (3) the donor displacement, driven by the energy of an occupied antibonding orbital, resembles a strong Jahn-Teller effect but differs because of the large potential barrier between the centered (T2) donor state and the distorted deep state. This model provides a natural explanation for the bulk of the data published on DX centers, especially the large barrier for thermal capture and the far-infrared absorption spectra reported by Theis et al. for the 1s-2p transition in Si-doped AlxGa1-xAs. The far-infrared absorption spectra indicate that the lowest state of symmetry A1 lies where it is expected, about 70 meV below the L conduction-band edge, or nearly 100 meV above the deep DX level. © 1986 The American Physical Society.