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High-Mobility Quantum Wires Fabricated by Ga Focused Ion Beam Shallow Implantation

High-mobility quantum wires are fabricated using shallow implantation of a low energy focused Ga ion beam into a modulation doped AlxGa1-xAs/GaAs heterostructure. Lowering the implant energy keeps the implanted ions away from the two-dimensional electron gas and reduces crystallographic damage. The electron mobility is 5.0×105 cm2/V·s for the wires 10 µm long with an effective width of 0.152 µm, which is much higher than that for previous wires. The effective wire width is independently derived from two measurements: (1) four-terminal conductance at zero-magnetic field and (2) the magnetic depopulation effect in the Shubnikov-de Haas oscillation. As the implantation dose decreases, the electron mobility increases with an effective width of more than 2.1-µm, while it is nearly constant for narrower wires. This suggests the existence of unintentionally implanted neutral Ga atoms and/or stray Ga ions.