A simple and reliable process for ohmic contacts to AlxGa1-xAs/GaAs he
terostructures is presented. The key feature is the use of niobium ref
ractory metal as a barrier between the eutectic AuGe alloy and the cap
ping Au layer, leading to excellent contact morphology and good electr
ical properties. Such ohmic contacts fabricated for a two-dimensional
electron gas have achieved a resistance of 0.2 Omega mm. The smooth mo
rphology allows subsequent electron beam lithography alignment to the
ohmic level, and is crucial for short-gate transistors.