Negative and persistent photoconductivity in p-type Al0.5Ga0.5As/GaAs/Al0.5Ga0.5As heterostructures under uniaxial stress

Illumination of a double p-Al0.5Ga0.5As/GaAs/Al0.5Ga0.5As heterostructure b y a red light emitting diode results in a negative photoconductivity that, after the diode is switched off, slowly relaxes to a positive persistent ph otoconductivity, characterised by an approximately 1.5-fold increase of the two-dimensional hole concentration. This metastable state may be explained with a model in which deep electron traps are supposed to be located above the Fermi level on the inverted heterointerface. Under uniaxial compressio n the hole concentration in the persistent photoconductivity state, as well as in the dark state, demonstrates the same linear decrease.