Stable conductance plateaus from ridge wires grown on a patterned substrate

A (100)-GaAs substrate was prepatterned with Hall-bar mesas incorporating a constriction, subsequent molecular beam epitaxial overgrowth of a GaAs∕AlGaAs quantum well resulted in narrowed constrictions and creation of conducting wires. Constrictions parallel, perpendicular, and diagonal to [01¯1], of up to 30μm in length, were investigated. Cross-sectional scanning electron microscopy images were correlated with the electrical conductance characteristics. Quantized conductance plateaus were only observed in the [01¯1] oriented wires, where the growth process formed an apex. Measurement stability was achieved by returning to a large negative top gate voltage, thus, plateaus reproducibly retraced themselves as a function of top gate voltage, and were flat and well resolved.