A trilevel resist system was employed to fabricate self-aligned, submicron emitter finger In(0.52)Al(0.48)As/In(0.42)Ga(0.58)As(0.77)Sb(0.23)/In(0.53)Ga(0.47)As double heterojunction bipolar transistors (DHBTs). Selective wet-etchants were used to define the emitter fingers and to form an InGaAs guard-ring around the emitter fingers. Due to the low energy bandgap of the InGaAsSb base layer and type II base-collector junction, a low turn-on voltage of 0.38 V at 1 A/cm(2) and a high dc current gain of 123.8 for a DHBT with a 0.65 x 8.65 mu m(2) emitter area were obtained. A unity gain cutoff frequency (f(T)) of 260 GHz and a maximum oscillation frequency (f(max)) of 485 GHz at J(C) = 302 kA/cm(2) were achieved. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3589808]
