Metallurgical stability of ohmic contacts on thin base InP/InGaAs/InP HBT's

The metallurgical stability of ohmic contacts: Pt, Pt/Ti, Au/Ti, Au/Pt/Ti, and Au/Pt/Ti/W, on a 500 /spl Aring/ thick p/sup +/-InGaAs base of InP/InGaAs/InP HBTs have been investigated as a function of anneal temperature. All contacts were stable after a 300/spl deg/C-30 s anneal. Pt contact failed at 350/spl deg/C whereas Pt/Ti, Au/Ti, and Au/Pt/Ti contacts failed at 400/spl deg/C. The failure mechanism was a collector leakage short owing to the penetration of Pt or Ti through the thin base. Only HBTs with Au/Pt/Ti/W contact were still functional after a 400/spl deg/C anneal with no apparent shift in the turn-on voltage for the emitter and collector junctions.