Growth of 100 GHz SiGe-Heterobipolar Transistor (HBT) Structures

Abstract

The transit frequency f T of SiGe-heterobipolar transistors (HBT's) was increased from 20 GHz to 100 GHz. This was mainly achieved by thickness reduction of the double heterojunction SiGe-base from 65 nm to 25 nm. The complete vertical structure of the SiGe-HBT's (collector, base, emitter, emitter contact) was grown in one run by Si molecular beam epitaxy (Si-MBE). The growth temperature was varied from 650° C at the collector side to 325° C at the emitter contact side. The different n-type doping levels (10 17 / cm 3 , 10 18 / cm 3 , 10 20 / cm 3 ) were obtained by applying three different Sb-doping techniques (secondary implantation, adatom pre build-up, low temperature doping). The p-type base was doped with boron. The doping level in the base (6×10 19 / cm 3 ) exceeded the emitter doping level by a factor of 30 (doping level inversion).