Current Controlled Negative Differential Conductance in Electron Waveguide Structures

An investigation of the current-voltage characteristics of electron waveguides formed in 2-dimensional electron gas was performed at low temperatures. The nanometer scale waveguides were fabricated using a split-gate technique on GaAs/AlGaAs uniformly modulation doped heterostructure. Depending upon the thermal and illumination histories of the waveguide device, the current-voltage characteristics fell into two categories; ideal point contact behavior and current controlled negative differential conductance. In some cases multiple current controlled negative differential conductance behavior was found. The current-voltage characteristics could be controllably and reversibly changed from one category to the other by a combination of illumination and annealing of the device. This suggested that ionization of the donor atoms determined the type of current-voltage behavior observed. Ionized donors were believed to cause inhomogeneities in the background electrostatic potential of the waveguide. When the gates were biased sufficiently negative, the formation of a puddle of electrons in the waveguide was possible if inhomogeneities in the confinement potential were present. The current controlled negative differential conductance was believed to be due to the thermal runaway of hot carriers heated by electrons thermionically emitted into the puddle. Some devices showed current-voltage characteristics with multiple regions of current controlled negative differential conductance. These were attributed to the interaction of two or more puddles of heated electrons in the waveguide.