Effects of displaced p-n junction of heterojunction bipolar transistors

Abstract

Two-dimensional simulations that demonstrate the effects of displacements of the p-n junctions from the heterojunctions of symmetrical Al/sub 0.28/Ga/sub 0.72//GaAs double-heterojunction bipolar transistors (DHBTs) are reported. When the emitter and/or collector p-n junctions do not coincide with the AlGaAs/GaAs heterojunctions, the electrical characteristics are shown to be drastically altered due to changes in the potential profiles and to changes in recombination rates both in the neutral base and in the space-charge region of the emitter. The effects of a small displacement of the p-n junction from the emitter-base or the base-collector heterojunctions are examined and results for current gain beta and cutoff frequency f/sub T/ are given that demonstrate enhanced performance for DHBTs with p-n junctions that are not coincident with the heterojunctions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>