Planar quantum transistor based on 2D–2D tunneling in double quantum well heterostructures

We report on our work on the double electron layer tunneling transistor (DELTT), based on the gate control of two-dimensional–two-dimensional (2D–2D) tunneling in a double quantum well heterostructure. While previous quantum transistors have typically required tiny laterally defined features, by contrast the DELTT is entirely planar and can be reliably fabricated in large numbers. We use a novel epoxy-bond-and-stop-etch flip-chip process, whereby submicron gating on opposite sides of semiconductor epitaxial layers as thin as 0.24 μm can be achieved. Because both electron layers in the DELTT are 2D, the resonant tunneling features are unusually sharp, and can be easily modulated with one or more surface gates. We demonstrate DELTTs with peak-to-valley ratios in the source-drain I–V curve of order 20:1 below 1 K. Both the height and position of the resonant current peak can be controlled by gate voltage over a wide range. DELTTs with larger subband energy offsets (∼21 meV) exhibit characteristics that are nearly as good at 77 K, in good agreement with our theoretical calculations. Using these devices, we also demonstrate bistable memories operating at 77 K. Finally, we briefly discuss the prospects for room temperature operation, increases in gain and high speed.