NONEQUILIBRIUM RANDOM TELEGRAPH SWITCHING IN QUANTUM POINT CONTACTS

We have investigated nonequilibrium transport through quantum point co ntact structures in high mobility GaAs/AlGaAs heterostructure. For low source-drain bias the current-voltage characteristics show the expect ed conductance quantization. At biases above approximately 6 mV, condu ctance instabilities in the DC current-voltage characteristics are obs erved which depend on the thermal and light exposure history of the sa mple. Time-dependent measurements in the regions of instability reveal that random telegraph switching (RTS) between well-defined differenti al conductance states is occurring. The RTS has been studied as a func tion of source-drain and gate bias, as well as temperature. The averag e time in the low and high states is found to depend exponentially on the source-drain and gate bias around some critical bias point. This c ritical point appears to correspond to a transition when an extra quas i one-dimensional subband crosses the Fermi level. The origin of the s witching is believed to be associated with the charging and dischargin g of shallow donor defects due to DX centers in the AlGaAs.