Reliability analysis of GaAs/AlGaAs HBTs under forwardcurrent/temperature stress

摘要

The reliability of GaAs/AlGaAs heterojunction bipolar transistorsis investigated by accelerated life-testing of discrete devices underforward bias stress at elevated temperatures. The DC devicecharacteristics are monitored to evaluate the effect of bias/temperaturestress on a large number of devices fabricated on MBE (molecular beamepitaxy) grown material. The primary degradation observed in somedevices is a reduction in the current gain which appears to be due to anelectric field-aided diffusion of interstitial Be from the base into thebase-emitter graded region. Other devices with optimal epitaxialmaterial show stable current gain after DC bias stress at hightemperature. Ohmic contact degradation, with or without bias, is alsoobserved at the emitter contact, resulting in an increased emitterseries resistance