Performance and Stability of MOVPE-Grown Carbon-Doped InP/InGaAs HBT's Dehydrogenated by an Anneal after Emitter Mesa Formation

A high-temperature anneal of 500°C for 5 min after emitter mesa formation is effective in completely reversing the hydrogen passivation of carbon acceptors in InP/InGaAs heterostructure bipolar transistors. Fabricated devices show a base hole concentration as high as 5 ×1019 cm-3 and a maximum oscillation frequency above 200 GHz. However, this technique simultaneously causes damage to the emitter mesa surface and degrades current gain. In order to avoid such undesirable effects, one has to carefully optimize the anneal conditions and/or select the optimum crystallographic orientation of the emitter mesa so as to increase the thermal stability of InP sidewalls. Preliminary bias-temperature stress tests were also performed to examine the stability of base-emitter junctions. The results show that the stability strongly depends on the emitter mesa orientation. Promising results are obtained from devices whose emitter orientation is parallel to the Primary Flat of (100)-oriented InP substrates.