BASE METALLIZATION STABILITY IN INP INGAAS HETEROJUNCTION BIPOLAR-TRANSISTORS AND ITS INFLUENCE ON LEAKAGE CURRENTS/

For InP/InGaAs heterojunction bipolar transistors (HBTs), base-collect or leakage current can be quite impairing by restricting their operati onal conditions to a very narrow emitter-collector voltage range. Resu lts of a study on morphological degradations of various p-type metalli zations to InGaAs and their effect on base-collector leakage current o f InP/InGaAs double HBTs are reported here. Two kinds of base contacts were investigated. Mn/Au/Ti/Au induces high leakage current after con tact annealing at temperatures as low as 300 degrees C. This is due to important interdiffusion of the species, and precipitation inside the base layer. Ti/Pt/Au is a good alternative, provided that the platinu m layer is not too thick, and the contact annealing temperature not to o high. Leakage current was found to be related to the strain induced by metal deposition, or to the morphological degradation taking place during annealings at high temperatures (metal precipitates formation i nside the base layer inducing strain, and III-V elements exodiffusion) . However, HBTs with Ti/Pt/Au base contacts annealed at 300 degrees C showed no excess leakage current and almost no morphological alteratio n, and contact resistances below 10(-5) Omega cm(2) were obtained for base doping levels above 10(19) cm(-3). (C) 1997 American Vacuum Socie ty.