On the annealing mechanism of AuGe/Ni/Au ohmic contacts to a two-dimensional electron gas in GaAs/AlxGa1-xAs heterostructures

Ohmic contacts to a two-dimensional electron gas (2DEG) in GaAs/AlxGa1-xAs heterostructures are often realized by annealing of AuGe/Ni/Au that is deposited on its surface. We studied how the quality of this type of ohmic contact depends on the annealing time and temperature, and how optimal parameters depend on the depth of the 2DEG below the surface. Combined with transmission electron microscopy and energy-dispersive x-ray spectrometry studies of the annealed contacts, our results allow for identifying the annealing mechanism. We use this for proposing a model that can predict the optimal annealing time when our commonly applied recipe is used for a certain heterostructure at a certain temperature.