Magnetic freeze-out study of the DX-linked shallow level in Si-doped AlxGa1-xAs under hydrostatic pressure

Magnetic freeze-out experiments under hydrostatic pressure have been performed in the temperature range 4.2-77 K on direct-band-gap Si-doped AlGaAs samples. Successive illuminations have been used to monitor the concentrations of the metastable shallow states arising from the DX centres. With increasing concentrations of those states, evidence is given for an insulator-metal transition confirming the Gamma character of these shallow impurity states. Moreover a shallow-deep transition is shown to hold at X=0.32 as a result of the appearance in the gap at x=0.30 of a localized level also originating from the DX centre but with no potential barrier for carrier capture.