Composition-Graded AlInP/AlGaAsSb/InP Type-II DHBTs With $f_{T}/f_{\rm MAX} = \hbox{450/510}\ \hbox{GHz}$

A type-II AlInP/AlGaAsSb/InP double heterojunction bipolar transistor (DHBT) with composition-graded Al content in the base is designed and grown by molecular beam epitaxy. Compared with composition-graded GaAsSb and InGaAsSb bases in DHBT, the graded AlGaAsSb base can generate a larger built-in electric field, thus reducing base transit time and improving device speed. We have fabricated AlGaAsSb graded base DHBTs and demonstrated f
_T
/f
_MAX
= 450/510 GHz for a 0.3 × 2 μm
²
device.