  We present overlapping top gate electrodes for the formation of gate defined
lateral junctions in semiconducting layers as an alternative to the back
gate/top gate combination and to the split gate configuration. The optical
lithography microfabrication of the overlapping top gates is based on multiple
layers of low-temperature atomic layer deposited hafnium oxide, which acts as a
gate dielectric and as a robust insulating layer between two overlapping gate
electrodes exhibiting a large dielectric breakdown field of > 1E9 V/m. The
advantage of overlapping gates over the split gate approach is confirmed in
model calculations of the electrostatics of the gate stack. The overlapping
gate process is applied to Hall bar devices of mercury telluride in order to
study the interaction of different quantum Hall states in the nn', np, pn and
pp' regime.
