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Base metallization stability in InP/InGaAs heterojunction bipolar transistors and its influence on leakage currents

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7 Author(s)
Caffin, D. ; France Telecom, CNET-PAB, Laboratoire de Bagneux, BP 107, 92225 Bagneux Cedex, France ; Besombes, C. ; Bresse, J.F. ; Legay, P.
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For InP/InGaAs heterojunction bipolar transistors (HBTs), base–collector leakage current can be quite impairing by restricting their operational conditions to a very narrow emitter–collector voltage range. Results of a study on morphological degradations of various p-type metallizations to InGaAs and their effect on base–collector leakage current of InP/InGaAs double HBTs are reported here. Two kinds of base contacts were investigated. Mn/Au/Ti/Au induces high leakage current after contact annealing at temperatures as low as 300 °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 platinum layer is not too thick, and the contact annealing temperature not too 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 inside the base layer inducing strain, and III–V elements exodiffusion). However, HBTs with Ti/Pt/Au base contacts annealed at 300 °C showed no excess leakage current and almost no morphological alteration, and contact resistances below 10-5 Ω cm2 were obtained for base doping levels above 1019cm-3. © 1997 American Vacuum Society.

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Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures  (Volume:15 ,  Issue: 4 )