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_c=30 KA/cm² a current gain cutoff frequency, f_T, of 51 GHz and a maximum oscillation frequency, f_max of 160 GHz despite their thick base (150 nm) and collector (450 nm) layers. The f_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_c C_BC)_eff=f_T/(8πf_max ²) is as small as 78 fs