ABSTRACT
InGaP/GaAs heterojunction bipolar transistors (HBT's) with excellent high-frequency performance have been developed. A cut-off frequency fT of 150 GHz is achieved by using an ultra-thin base layer of 15 nm. The base transit time τB is estimated from both DC and RF characteristics and it shows quadratic dependence on the base thickness WB when WB is larger than 30 nm, whereas it tends to show linear dependence at smaller WB. This result indicates that nonequilibrium electron transport occurs at WB of less than 30 nm.
