HIGH F-MAX ALGAAS/GAAS HBTS WITH PT/TI/PT/AU BASE CONTACTS FOR DC TO 40 GHZ BROAD-BAND AMPLIFIERS

A low contact resistivity of 4.4 x 10(-7) Omega cm(2) for AlGaAs/GaAs HBTs was realized using Pt/Ti/Pt/Au base metal and a 8 x 10(19) cm(-3) highly-doped base. A high f(max) of 170 GHz was achieved by reducing a base resistance. The formation of oxide-free interface between an AlGaAs graded base and Pt-based metal was demonstrated with Auger electron spectroscopy. The optimization of the growth condition conquered the rapid current-induced degradation in the highly Be-doped HBTs. An extremely wide bandwidth of 40 GHz was attained by a Darlington feedback amplifier fabricated using these high-f(max) HBTs. These properties indicate that the application of AlGaAs/GaAs HBTs can be expected to extend to future ultrahigh-speed optical transmission systems.