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The study of electron transport in low-dimensional systems is of importance,not only from a fundamental point of view, but also for future electronic andspintronic devices. In this context heterostructures containing atwo-dimensional electron gas (2DEG) are a key technology. In particularGaAs/AlGaAs heterostructures, with a 2DEG at typically 100 nm below thesurface, are widely studied. In order to explore electron transport in suchsystems, low-resistance ohmic contacts are required that connect the 2DEG tomacroscopic measurement leads at the surface. Here we report on designing andmeasuring a dedicated device for unraveling the various resistancecontributions in such contacts, which include pristine 2DEG series resistance,the 2DEG resistance under a contact, the contact resistance itself, and theinfluence of pressing a bonding wire onto a contact. We also report here arobust recipe for contacts with very low resistance, with values that do notchange significantly for annealing times between 20 and 350 sec, henceproviding the flexibility to use this method for materials with different 2DEGdepths. The type of heating used for annealing is found to strongly influencethe annealing process and hence the quality of the resulting contacts.

Robust recipe for low-resistance ohmic contacts to a two-dimensional electron gas in a GaAs/AlGaAs heterostructure