  Electrostatic gates are of paramount importance for the physics of devices
based on high-mobility two-dimensional electron gas (2DEG) since they allow
depletion of electrons in selected areas. This field-effect gating enables the
fabrication of a wide range of devices such as, for example, quantum point
contacts (QPC), electron interferometers and quantum dots. To fabricate these
gates, processing is usually performed on the 2DEG material, which is in many
cases detrimental to its electron mobility. Here we propose an alternative
process which does not require any processing of the 2DEG material other than
for the ohmic contacts. This approach relies on processing a separate wafer
that is then mechanically mounted on the 2DEG material in a flip-chip fashion.
This technique proved successful to fabricate quantum point contacts on both
GaAs/AlGaAs materials with both moderate and ultra-high electron mobility.
