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Effects of alloying and bias stress on the base contacts of AlGaAs/GaAs HBTs

The stability of AlGaAs/GaAs Heterojunction Bipolar Transistors (HBTs) with discretion to different base metal ohmic contact systems were studied by means of thermal alloying and current stress. The ohmic contacts studied were Au/Zn/Au and Ti/Au. It was found that after thermal alloying, though the Au/Zn/Au base contacts gave the lower base resistance, devices with Ti/Au contacts were more thermally reliable. With current stress, though alloyed Ti/Au devices gave a more reliable performance than Au/Zn/Au, they are still not optimum for long term device operation.