Engineering lateral quantum interference devices using electron beam lithography and molecular beam epitaxy

Abstract

Various new lateral quantum interference devices (QIDs) have been facbricated using high resolution electron beam lithography and molecular beam epitaxy. These QIDs utilize various nanometer scale electrodes to introduce electrostatic potential barriers in the electron gas at an AlGaAs/GaAs heterojunction. At low temperatures, as the electron mean free path approaches the dimensions of the gate electrode, quantum interference of the electron wave with the barriers and wells creates quasibound states that result in conductance oscillations as the gate voltage is scanned. High resolution electron beam lithography is used to define the nanometer gates, readily allowing the definition and alignment of different electrodes on the same wafer. A planar implantation isolation step is used to facilitate the liftoff of the Ti/Au gates patterned in polymethyl methacrylate (PMMA). Several novel QIDs will be described; emphasis will be on a new lateral double barrier resonant tunneling diode formed by two 80 nm gates separated by 100 nm. At 4.2 K, structure in the drain current is seen as the gate voltage is scanned for drain voltages less than 5 mV.