Large- versus small-lattice-relaxation models of theDXcenters inGa1−xAlxAs

The first observation of a metastable delocalized bound state of DX centers in ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Al}}_{\mathrm{x}}$As:Te pinned to the X minimum of the conduction band is reported. DX centers are therefore the first defects in covalent semiconductors that bind carriers in two barrier-separated states which are either strongly localized or delocalized. This validates the general Toyozawa model of extrinsic self-trapping for covalent materials, as well as the large-lattice-relaxation model of these centers.