ABSTRACT
Nonalloyed ohmic contacts: Au/Ti, Pt/Ti, and Au/Pt/Ti, have been found to be thermally unstable and unreliable on a 500Å-thick p+-InAsGa base of InP/InGaAs/InP HBTs at 400°C. Pt contact failed at 350°C. Pt or Ti penetrated through the thin base causing a serious leakage short across the base-collector junction and rendering the devices no longer functional. Using Au/Pt/Ti/W as contact, HBTs have been shown to remain functional after a 400°C anneal with no apparent shift in the turn-on voltage for the emitter and collector junctions.
