Novel approach for InP-based ultrafast HBTs

In this paper we propose and demonstrate a novel approach for improving high frequency performance of InP-based HBTs. A new structure, the Metal Heterojunction Bipolar Transistor (MHBT) where the semiconductor is replaced by a metal in the collector layer is described. This structure not only ensures high dynamic characteristics, but also provides satisfactory static behavior. MHBT demonstrators manufactured for this study show at J/sub c/=30 KA/cm/sup 2/ a current gain cutoff frequency, f/sub T/, of 51 GHz and a maximum oscillation frequency, f/sub max/ of 160 GHz despite their thick base (150 nm) and collector (450 nm) layers. The f/sub max/ value is, for this non-optimized structure, in the range of the best values reported for InP-HBTs. In addition the effective delay time (R/sub c/C/sub BC/)/sub eff/=f/sub T//(8/spl pi/f/sub max//sup 2/) is as small as 78 fs.