Deep levels in MBE grown AlGaAs/GaAs heterostructures

We have studied the deep levels in modulation-doped GaAs/Al0.33Ga0.67As heterostructures grown on (0 0 1) GaAs substrates with a high-mobility two-dimensional electron gas (2DEG), by means of current-mode deep level transient spectroscopy (I-DLTS). Five major traps have been identified and their effect on the 2DEG electron mobility and density has been assessed by comparing results from devices grown with different As/Ga ratios (25, 40 and 48). Two so-called "hole-like" traps have also been observed and we suggest they are linked to the different threshold voltages observed in the different devices studied. By utilizing different polarization conditions we were able to assign an origin to some of the traps and to advance hypotheses on their localization within the GaAs/Al0.33Ga0.67As heterostructures.