Physical origin of the D X 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.