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Three different elements, silicon, selenium, and tellurium, are ion-implanted in gallium arsenide to form a conducting layer that serves as a back-gate to a molecular beam epitaxy overgrown two-dimensional electron gas. While the heavy ion tellurium creates too many defects in the gallium arsenide to form a conducting layer, both silicon and selenium show promising results combined with MBE-grown high-quality 2DEGs. Similar 2DEG mobilities compared to non-implanted reference samples are achieved for both silicon and selenium implanted structures. Individual contacts to the back-gate are challenging. However, silicon implanted structures, annealed before the MBE growth, result in a functional back-gate, and the electron density of the 2DEG can be tuned via the structured back-gate. [ABSTRACT FROM AUTHOR]

Two dimensional electron gases (2DEGs) realized at GaAs/AlGaAs single interfaces by molecular-beam epitaxy (MBE) reach mobilities of about 15 million cm2 V s−1 if the AlGaAs alloy is grown after the GaAs. Surprisingly, the mobilities may drop to a few millions for the identical but inverted AlGaAs/GaAs interface, i.e. reversed layering. Here we report on a series of inverted heterostructures with varying growth parameters including temperature, doping, and composition. Minimizing the segregation of both dopants and background impurities leads to mobilities of 13 million cm2 V s−1 for inverted structures. The dependence of the mobility on electron density tuned by a gate or by illumination is found to be the identical if no doping layers exist between the 2DEG and the respective gate. Otherwise, it differs significantly compared to normal interface structures. Reducing the distance of the 2DEG to the surface down to 50 nm requires an additional doping layer between 2DEG and surface in order to compensate for the surface-Schottky barrier. The suitability of such shallow inverted structures for future semiconductor-superconductor hybrid systems is discussed. Lastly, our understanding of the improved inverted interface enables us to produce optimized double-sided doped quantum wells exhibiting an electron mobility of 40 million cm2 V s−1 at 1 K. [ABSTRACT FROM AUTHOR]