Type-II InP/GaAsXSB1−X DHBTs with simultaneous FT and FMAX >340 Ghz fabricated by contact lithography

InP/GaAsSb/InP DHBTs with 125 and 150 nm collector thicknesses were fabricated by optical contact lithography in a standard triple mesa process. It is shown that a peak current-gain cut-off frequency f_T = 343 GHz and maximum oscillation frequency f_MAX = 351 GHz were simultaneously achieved on devices with an emitter area of 0.6 × 11.5 μm² and a 150 nm collector. To the best of our knowledge, these are the first InP/GaAsSb DHBTs to offer balanced figures-of-merit exceeding 300 GHz and a current gain β > 60. Similar devices with a thinner collector (125 nm) exhibit a peak f_T = 377 GHz with f_MAX = 318 GHz due to the interplay between a reduced collector transit time and the increased collector-base depletion capacitance. For the devices under study, the extrinsic collector-base capacitance was observed to have a small impact on f_MAX. However, the base mesa over-etching is essential to reduce the extrinsic capacitance and thus improve f_T.