An on-ledge Schottky potentiometer for the diagnosis of HBT emitterpassivation

摘要

A Schottky diode, which contacts the emitter passivation ledgedirectly, is used as a potentiometer to monitor the effectiveness of theemitter/base junction passivation in AlGaAs/GaAs heterojunction bipolartransistors (HBTs). The function and mechanism of this on-ledgepotentiometer are carefully examined and analyzed. With this on-ledgeSchottky diode, the emitter ledge potential (V_Ledge) can bemeasured directly as a function of the base-emitter bias voltage (VBE)By relating V_Ledge to V_BE, We are able to quantifythe extent of the ledge depletion down to a few angstroms (<10Å) in precision. The outstanding detectivity of the on-ledgepotentiometer makes itself a very powerful tool in the diagnosis of HBTproblems in both device operation and long-term reliability. Theseproblems are not detectable or distinguishable with prior monitoringtechniques