Abstract

Superior DC and RF performance are obtained using InGaP/GaInAsN and InP/GaInAs double heterojunction bipolar transistors with compositionally graded base layers. By grading the base layer energy band-gap, we achieve nearly a 100% improvement in DC current gain and as much as a 15% increase in the unity gain cutoff frequency (ft) relative to baseline constant-composition base layer devices. In InGaP/GaInAsN DHBTs, DC current gains as high as 250 and cutoff frequencies of 60 GHz are demonstrated for devices with a collector thickness of 400 nm and BVceo values of 8.4 Volts. Graded-base InP/InGaAs DHBTs with an ft of 135 GHz are also demonstrated. Estimations of the ft*BVceo figure-of-merit are used to compare performance of these devices to existing technologies.