High-speed composite-collector InGaP/InGaAs/GaAs HBTs

This paper describes the design, simulation and measurement of a 100GHz R and Fmax HBT in which a p-type collector is combined with compositional grading in both the collector and base to provide optimum velocity overshoot. The composite-collector HBT (CCHBT) was designed using an in- house 1-D Schrodinger-Poisson-Continuity solver which includes the effects of velocity overshoot and tunnelling through an extended drift-diffusion formalism. The devices were grown by MOCVD on 4" wafers and processed using NORTEL's standard 65/95 GHz Ft/Fmax HBT process. The CCHB'A demonstrated peak values of 103GHz Ft and 102GHz Fmax. Current gains exceeding 200 were measured along with transconductance of over 120 mS for a 6.5x 3mum HBT. The breakdown voltage BVcbo, was in excess of 12V with BVceo and BVebo greater than 6V.