Over 300 GHz fT and fmax InP/InGaAs double heterojunction bipolar transistors with a thin pseudomorphic base

We describe 150-nm-thick collector InP-based double heterojunction bipolar transistors with two types of thin pseudomorphic bases for achieving high f(T) and f(max). The collector current blocking is suppressed by the compositionally step-graded collector structure even at J(C) of over 1000 kA/cm(2) with practical breakdown characteristics. An HBT with a 20-nm-thick base achieves a record f(T) of 351 GHz at high J(C) of 667 kA/cm(2), and a 30-nm-base HBT achieves a high value of 329 GHz for both f(T) and f(max). An equivalent circuit analysis suggests that the extremely small carrier-transit-delay contributes to the ultrahigh f(T).