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

摘要

The high frequency performance of type-Ⅱ InP/GaAsSb 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 mA/μm~2. The peak f_T of a graded base device with 0.38X8 μm~2 emitter dimensions improves from 505 GHz at 25℃ to 535 GHz at -55℃ as determined by -20 dB/decade extrapolation. The base grading has reduced the total transit time by 25% compared to the uniform base type-Ⅱ DHBT.