Electrical and thermal stability of AuGeNi ohmic contacts to GaAs fabricated with in situ RF sputter cleaning

In situ RF sputter cleaning of the GaAs surface before the AuGeNi deposition gave low contact resistance Rc {reversed tilde equals} 0.1 Ω-mm. When the contacts were annealed at 400°C for 57 hours, Rc ≤ 0.6 Ω-mm was obtained. This is still an acceptable value for 1 μm gate MESFET process. With low sputtering voltages or short sputtering times, contact resistance was large and non-uniform. Normally a short alloying time of 2 min at 440°C is used for ohmic contact formation. For the process described here, alloying times as long as 15 min at 430°C gave low contact resistance Rc {reversed tilde equals} 0.2 Ω-mm. When the AuGe films were deposited from two separate sources of Au and Ge ("layered" process) low contact resistances Rc {reversed tilde equals} 0.2 Ω-mm were obtained. However, this "layered" process did not show the same kind of uniformity and low contact resistance that was obtained when the AuGe film was deposited from a single "eutectic" source. © 1986.