Performance enhancement of composition-graded-base type-II InP/GaAsSb double-heterojunction bipolar transistors with f T>500 GHz

Abstract

The high frequency performance of type-II InPGaAsSb double heterojunction bipolar transistors (DHBTs) with compositionally graded and uniform 25 nm base layers and 65 nm InP collectors is investigated. The graded base DHBT achieves a peak current gain of 20.5 compared to 14.9 for the uniform base DHBT at current densities near 15 mAμ m2. The peak fT of a graded base device with 0.38×8 μ m2 emitter dimensions improves from 505 GHz at 25 °C to 535 GHz at -55 °C as determined by -20 dBdecade extrapolation. The base grading has reduced the total transit time by 25% compared to the uniform base type-II DHBT. © 2006 American Institute of Physics.