First Principle Calculation of the DX-CenterGround-States in GaAs, AlxGa1-xAs Alloysand AlAs/GaAs Superlattices

Abstract

The atomistic nature of the deep donor levels referred to as DX centers in GaAs, Al x Ga 1- x As alloys and AlAs/GaAs superlattices is investigated by applying the ab initio self-consistent pseudopotential method to 64-atom super cells. The total energy and force calculations reveal that the most stable state is the T d -distorted atomic configuration around a substitutional donor with the neighbouring bond relaxation given by the effective ionic radius (0.7% for Si G a ). On the contrary, a negatively charged donor with broken-bond configuration is shown to give a metastable state and not the ground state even under high hydrostatic pressures. It is found that a deep A 1 level attributable to the DX center is induced by a simple substitutional donor with the obtained optimal lattice configuration. The theory successfully explains experimental results on the thermal and optical ionization energies for the DX centers.