LOW-TEMPERATURE OCCUPATION OF A DONOR STATE RESONANT WITH THE CONDUCTION-BAND IN AL0.35GA0.65AS

n(H) (Hall) and n(CV) (capacitance-voltage) electron density data are compared in a Si-doped Al0.35Ga0.65As sample having an N-d - N alpha = 2.8 x 10(18) cm(-3) net donor density. Data taken during low-temperature photoionization of DX centers and during temperature variations in the persistent photoconductivity regime (T < 50 K) suggest that as the density of photoexcited electrons increases the Fermi energy rises until a Si-related D-o donor bound state, resonant in energy with the Gamma conduction-band valley, becomes populated. During the initial stage of isothermal capture transients, n(H) is found to decrease at a slower time rate than n(CV), since electrons are continuously supplied in the Gamma valley by the:depopulation of the DO level. During the final stage of the capture, when D-o is empty, n(CV) and nH are found to coincide. The analysis based on an equilibrium distribution of the photoexcited electrons between the Gamma valley and the D-o level gives for this latter an energy of 40.6 +/- 0.5 meV; above the <Gammar> minimum (T = 0). The possibility that the D-o state is linked to the X secondary minima of the conduction band is discussed.