Tailoring ballistic injection

Efficient electron injection into nanoscale devices is difficult to experimentally characterize at the local scale. We discuss here how little modifications of the electrostatic potential landscape in the vicinity of a nanodevice injection leads can drastically enhance electron transmission, by tuning semi-classical trajectories and directly re-orienting charge flow in the desired paths. In this context, quantum rings (QRs) appear as interesting geometries since, in a semiclassical view, most electrons bounce against the hard-wall potential of the central QR antidot directly after injection. We found that a local partial depletion of the QR close to this hard-wall can counter-intuitively ease ballistic electron flow. On the contrary, local charge accumulation can focus the flow on the hard wall potential and increase back-scattering. Simulating current density distributions in the ring gives insights on these peculiar transmission conditions. Using a voltage-polarised scanning gate to tune in situ the ballistic electron flow in a QR patterned from a high mobility 2D electron system, we find a remarkable direct experimental confirmation of this particular phenomenology.