Physical origin of the <i>D</i> <i>X</i> center

Abstract

When intervalley mixing effects are large enough, they induce a sharp shallow deep instability for a substitutional impurity. We show that this is the case in GaAs for the ground state associated with the L valleys, which becomes located in the forbidden gap under hydrostatic pressure or in GaAlAs alloys, whereas the donor states associated to the Γ and X valleys remain shallow. This result accounts for the behavior of the so-called DX center.