Evidence for localized Si-donor state and its metastable properties in AlGaN

Transport studies of AlxGa1-xN (0.5 < x < 0.6) doped with Si have been perf ormed in the pressure range up to 1.4 GPa. For these alloys, the Si dopant forms two donor states. One of them has an effective mass character and the other one represents the localized state strongly coupled to the crystal l attice (metastable state). The localized state of Si forms the correspondin g level in the gap for x exceeding 0.5. For the higher x, an increase of th e activation energy of this state occurs. Metastable properties of the loca lized state of Si lead to a persistent photoconductivity effect and to a pr essure induced freeze-out of electrons. (C) 1999 American Institute of Phys ics. [S0003-6951(99)00725-1].