Nonequilibrium random telegraph switching in quantum point contacts

We have investigated nonequilibrium transport through quantum point contact structures in high mobility GaAs/AlGaAs heterostructure. For low source-drain bias the current-voltage characteristics show the expected conductance quantization. At biases above approximately 6 mV, conductance instabilities in the DC current-voltage characteristics are observed which depend on the thermal and light exposure history of the sample. Time-dependent measurements in the regions of instability reveal that random telegraph switching (RTS) between well-defined differential conductance states is occurring. The RTS has been studied as a function of source-drain and gate bias, as well as temperature. The average 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 critical point appears to correspond to a transition when an extra quasi one-dimensional subband crosses the Fermi level. The origin of the switching is believed to be associated with the charging and discharging of shallow donor defects due to DX centers in the AlGaAs.