Quaternary Graded-Base InP/GaInAsSb DHBTs With <inline-formula> <tex-math notation="LaTeX">${f}_{\text{T}}$ </tex-math> </inline-formula>/<inline-formula> <tex-math notation="LaTeX">${f}_{\text{MAX}}$ </tex-math> </inline-formula> = 547/784 GHz

Abstract

We report a “Type-II” metal-organic chemical vapor deposition (MOCVD)-grown compositionally graded quaternary base InP/GaInAsSb/InP double heterojunction bipolar transistor (DHBT) with simultaneous cutoff frequencies f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> /f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MAX</sub> = 547/784 GHz. Compositional grading of the As/In mole fractions enables stronger quasi-electric fields in the base and favors better RF performance. Consideration of the higher bandstructure reveals new insights on the performance limits of “Type-II” DHBTs: Indium incorporation in a GaAsSb base appears to increase the efficiency of electron injection from the base into the InP collector. The present results correspond to the fastest MOCVD-grown quaternary base DHBTs reported to date for a device with f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MAX</sub> > f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> .