Ultra-high f/sub max/ and f/sub T/ InP/InGaAs double-heterojunction bipolar transistors with step-graded InGaAsP collector

Abstract

The high-frequency performance of small scale InP/InGaAs DHBTs with InGaAsP in the collector that has a highly Zn-doped base was investigated using various emitter-widths and lengths as functions of collector current I/sub C/ and collector/emitter voltage V/sub CE/. Narrowing the emitter-width is significantly more effective for increasing f/sub max/ than shortening the emitter-lengths. A DHBT with a narrow 0.8-/spl mu/m emitter-metal has an ultra-high f/sub max/ of 267 GHz and f/sub T/ of 144 GHz at an I/sub C/ as low as 4 mA. This increase in f/sub max/ is attributed to the low product of the base resistance and reduced base/collector capacitance.