BASE-COLLECTOR LEAKAGE CURRENTS IN INP INGAAS DOUBLE-HETEROJUNCTION BIPOLAR-TRANSISTORS/

For InP/InGaAs HBT's, base-collector leakage current can restrict thei r operation to a narrow emitter-collector voltage range, We studied se veral factors that can degrade the leakage current: the base-collector junction design, the base mesa etching technique, and the base metall ization process. A step-graded base-collector heterojunction offered t he best results, A leakage free multiple step etching process, combini ng wet and dry etching, has been developed. Ti/Pt/Au is a suitable bas e metallization, provided that the platinum layer is not too thick, an d that the contact annealing temperature is not too high, Finally, ver y low leakage current HBT's were fabricated.