InP/GaAsSb DHBTs With Simultaneous $f_{\rm T}/f_{\rm MAX}=428/621~{\rm GHz}$

Type-II InP/GaAsSb double heterojunction bipolar transistors (DHBTs) with an f
_MAX
of 621 GHz and a simultaneous f
_T
of 428 GHz are demonstrated. A DC peak current gain β = 19 and a common-emitter breakdown voltage BV
_CEO
=5 V are measured for 0.2 × 4.4-μm
²
emitter devices featuring a 20-nm-thick graded GaAsSb base with a sheet resistance of 1077 Ω/□ and a 125-nm-thick more heavily doped InP collector enabling a higher Kirk current. The present transistors are the first InP/GaAsSb DHBTs with an f
_MAX
in excess of 600 GHz.