D. Caffin et al., BASE-COLLECTOR LEAKAGE CURRENTS IN INP INGAAS DOUBLE-HETEROJUNCTION BIPOLAR-TRANSISTORS/, I.E.E.E. transactions on electron devices, 44(6), 1997, pp. 930-936
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.