Extraction of the average collector velocity in high-speed NpN InP/GaAsSb/InP DHBTs

Abstract

Absfract-In "type-11'' NpN InPiGaAsSbiInP double heterostructure bipolar transistors (DHBTs), the p + GaAsSb base conduction band edge lies dEc above the InP collector conduction band: a small ballistic energy dEc is imparted to collected electrons as they are launched into the collector, The high initial velocity should in principle reduce the collector signal delay time. In the present work, we extract the average collector electron velocity in high-speed lnPiGaAsSbIInP DHBTs, and find a peak average velocity approaching 4 x lo7 c d s across a 2000 8, InP collector. This finding provides the first evidence of the performance advantage afforded by abrupt type-I1 BIC junctions for collector transport when compared to the conventional graded 'launchers' required when a GaInAs base layer is used.