Fabrication of 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 m2 emitter area were obtained. A unity gain
cutoff frequency
fT of 260 GHz and a maximum oscillation frequency
fmax of 485 GHz at JC
=302 kA/cm2 were achieved.