Relaxation of persistent photoconductivity inAl0.3Ga0.7As

Stretched-exponential decay of persistent photoconductivity (PPC) has been observed in ${\mathrm{Al}}_{0.3}$ ${\mathrm{Ga}}_{0.7}$As in the temperature region T<90 K. The decay time constant and exponent have been measured at different temperatures. Experimental results show that the thermal activated capture of electrons at the DX centers becomes negligible at T<40 K. However, a transition from a thermally activated to a nearly-temperature-independent tunneling capture at a temperature on the order of 40 K has been observed for the first time for ${\mathrm{Al}}_{0.3}$ ${\mathrm{Ga}}_{0.7}$As, which is consistent with the multiphonon-emission model for DX centers of large lattice relaxation.