Reliability characteristics of mesa-etched isolated emitter structure AlGaAs/GaAs HBTs with Be-doped base

High-temperature bias stress tests were carried out on AlGaAs/GaAs heterojunction bipolar transistors (HBTs) with a 5*10/sup 19/ cm/sup -3/ Be-doped base. It was shown that HBTs with a mesa-etched isolated emitter structure were more durable than ion-implanted isolated emitter structure HBTs in terms of switch-on voltage stability. This result implies that the base/emitter junction edge, which makes contact with the ion-implanted defect-rich region, plays an important role in reliability characteristics. The lifetime of mesa-etched isolated emitter structure HBTs was also considered. It was found that the lifetime was determined by a reduction in hfe. The mean time to failure was estimated at 9.6*10/sup 5/ hours at 25 degrees C.<
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