n⁺-GaAs Back-Gated Double-Quantum-Well Structures with Full Density Control

We present the fabrication of a novel double-quantum-well (DQW) structure, in which the upper electron layer is supplied via modulation doping while the lower one is fully induced through the field effect from an n ⁺-GaAs back gate. Low-temperature transport measurements demonstrate that two-dimensional electron gases with equally high mobilities are successfully formed in the lower as well as in the upper QWs. By this approach, the electron density in the lower layer can be controlled over a wide range with a small back-gate bias, and hence the electron-density distribution in the DQW can be tuned arbitrarily by using a front gate in conjunction with the back gate.