High-fT AlGaAs/InGaAs HBTs with reduced emitter resistance for low-power-consumption, high-speed ICs

This paper reports on high-performance AlGaAs/InGaAs HBTs with a markedly reduced emitter resistance (R_EE). The result of the emitter-resistivity analysis reveals that a compositionally graded-AlGaAs layer leads to a high resistivity. By improving the emitterdoping profile, the measured R_EE was reduced to 1/4 of that for our conventional HBT. As a result, f_T of 140 GHz for a 7.4 μm² HBT and 112 GHz (f_max of 250 GHz) for a 2.8 μm² HBT were achieved, which are 1.7-2.2 times higher than those of the conventional HBT.