Fabrication and Characterization of Self-aligned InAlAs/InGaAsSb/InGaAs Double Heterojunction Bipolar Transistors...

A trilevel resist system was employed to fabricate self-aligned,
submicron emitter finger In0.52Al0.48As/In0.42Ga0.58As0.77Sb0.23/
In0.53Ga0.47As 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/cm2
and a high dc current gain of 123.8 for a DHBT with a 0.65 × 8.65
μm2 emitter area were obtained. A unity gain cut-off frequency
(fT) of 260 GHz and a maximum oscillation frequency (fmax) of 485
GHz at JC = 302 kA/cm2 were achieved.