Ohmic contact penetration and encroachment in GaAs/AlGaAs and GaAs FETs

Hypoeutectic AuGe/Ni ohmic contacts on GaAs and GaAs/AlGaAs were characterized by SEM, TEM, and energy dispersive X-ray analysis. The two main components of the contact were confirmed to be NiGeAs islands distributed in an Au-Ga alloy. The NiGeAs islands were larger and more evenly distributed on GaAs MESFETs than on GaAs/AlGaAs MODFETs. Vertical penetration was impeded but not halted by AlGaAs. Since the contacts did not melt during the alloying cycle, there was no lateral encroachment observed.<
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