Negative differential conductance in quantum waveguides

We discuss far-from-equilibrium electron transport in quantum waveguide structures at low temperatures. On slowly cooling the devices in the dark, the current-voltage characteristics are found to be similar to those of a quantum point contact. Exposure to light at low temperature alters the characteristics dramatically, with one or more regions of current-controlled negative differential conductance occurring. The characteristics can be returned to their prelight condition by annealing the samples above 120 K, which indicates that the effect is associated with the occupancy of DX centers in the AlxGa1-xAs. We argue that the negative differential conductance arises from hot-electron bistabilities due to puddles of charge trapped in the waveguide by potential inhomogeneities associated with ionized DX centers.