Fabrication of Quantum Wires by Ga Focused-Ion-Beam Implantation and Their Transport Properties

Quantum wire structures are defined on a modulation-doped AlGaAs/GaAs wafer grown by MBE using highly resistive regions formed by focused-Ga-ion-beam scanning and subsequent annealing. These fabricated wires show positive magnetoconductance and universal conductance fluctuations at low temperature. A Schottky electrode is placed on these wires and magnetoresistance characteristics are measured by changing the gate voltage at a fixed temperature. Ballistic electron transport is confirmed for a short wire, 0.6 µm in length, whereas universal conductance fluctuations are observed for a long wire, 2.4 µm in length, and the relationship between the phase coherent length and the conductance is obtained asLin∝G0.7from the gate voltage dependence on fluctuation amplitude.