Transport in GaAs heterojunction ring structures

In earlier work we have shown that the split gate GaAsAlGaAs heterojunction FET has been a very useful system for obtaining 1D transport.^1,2 We have now extended this work to the construction of ring structures. Here, a ring of resist (outside diameter 2.2μm, inside diameter 0.4μm) is formed on the AlGaAs surface using Electron Beam Lithography, and is covered with metal, thereby forming a Schottky gate inside and outside the ring. Application of a negative voltage to the gates depletes the high-mobility 2D electron gas at the interface, except in a narrow annulus between the gates. The width of this ring-shaped 2D electron gas can be varied by changing the gate voltage. The magnetoresistance has been measured for T<100 mK and magnetic fields up to 13 Tesla. Aharonov-Bohm oscillations are observed with amplitudes approaching 5% of the total ring resistance, depending on gate voltage, and extending out to B∼1T. The quantum Hall effect is seen at high fields and yields unexpected non-zero plateaux in R_xx for narrow channels.