Charging of deep-level centers and negative persistent photoconductivity in modulation-doped AlGaAs/GaAs heterostructures

The relaxation kinetics of persistent photoconductivity in AlGaAs/GaAs modu lation-doped heterostructures due to charging of EL2- and DX-centers is inv estigated over a wide range of temperatures and excitation photon energies. The light-induced charging of these deep centers was found to lead to accu mulation of positive and negative localized charges, which give rise to pos itive and negative persistent photoconductivities, respectively. These posi tive and negative charges are accumulated in different parts of the heteros tructure. Their different characteristic times, and the different temperatu re dependences of these times, result in nonmonotonic time and temperature dependences of the persistent photoconductivity. Charging of EL2-centers in the GaAs buffer layer leads to negative persistent conductivity in the tem perature range 180-300 K, while the negative photoconductivity observed at the temperatures below 180 K is caused by excited states of DX-centers in t he n(+)-AlGaAs. (C) 1999 American Institute of Physics. [S1063-7826(99)0150 1-X].