  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 (MBE) overgrown two-dimensional electron gas (2DEG).
While the heavy ion Tellurium creates too many damages 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 mobility compared to
non-implanted reference samples is 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 function back-gate, and the electron density of the 2DEG is tuned via the
back-gate.
