Gated Magnetotransport in a Very-High Mobility GaAs/AlGaAs Quantum Well

The ability to control electron density and potential profile in a very-high mobility, modulation-doped GaAs/AlGaAs 2D electron system by potential gates is a key ingredient in realizing confinement of quasiparticles in the fractional quantum Hall effect. In this study, top-gated Hall bar samples were constructed on a 20-nm GaAs/AlGaAs 2D electron gas quantum well (QW) using a Si$_{3}$N$_{4}$ dielectric layer. Before the gate was processed, the wafer had an electron density $n=6.3\times 10^{11}$ cm$^{-2}$ and a mobility $\mu =1\times 10^7$cm$^{2}$/Vs at 300 mK. By magnetotransport measurements in the quantum Hall region we found that electrons can be depleted uniformly (from 5.64 to $0.6\times 10^{11}$cm$^{-2})$, and the $n$ vs. gate-potential shows simple capacitive characteristics in this range. The \textit{$\mu $} vs. $n$ can be described by a power law, $\mu =A\cdot n^{1.9}$. We discuss the applications of the gate technique for quantum transport studies in very-high mobility QWs at ultralow temperature region produced by nuclear demagnetization refrigerator. Ref. R. L. Willett, et al, Appl. Phys. Lett. 89, 242107 (2006)