1 research outputs found
The improved inverted AlGaAs/GaAs interface: its relevance for high-mobility quantum wells and hybrid systems
Two dimensional electron gases (2DEGs) realized at GaAs/AlGaAs single
interfaces by molecular-beam epitaxy (MBE) reach mobilities of about 15 million
cm^2/Vs 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 cm^2/Vs for inverted
structures. The dependence of the mobility on electron density tunes 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 50nm 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 cm^2/Vs at 1K.Comment: 19 pages, 9 figure