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

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Abstract
The relaxation kinetics of persistent photoconductivity in AlGaAs/GaAs modulation-doped heterostructures due to charging of EL2-and DX-centers is investigated over a wide range of temperatures and excitation photon energies. The light-induced charging of these deep centers was found to lead to accumulation of positive and negative localized charges, which give rise to positive and negative persistent photoconductivities, respectively. These positive and negative charges are accumulated in different parts of the heterostructure. Their different characteristic times, and the different temperature 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 temperature range 180–300 K, while the negative photoconductivity observed at the temperatures below 180 K is caused by excited states of DX-centers in the n+-AlGaAs.