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

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/mu m(2). The peak f(T) of a graded base device with 0.38x8 mu m(2) emitter dimensions improves from 505 GHz at 25 degrees C to 535 GHz at -55 degrees C 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. (c) 2006 American Institute of Physics.