A new InGap/AlGaAs/GaAs composite-emitter heterojunction bipolar transistors

This paper reported a new composite-emitter heterojunction bipolar transistor (CEHBT) with a composite emitter formed of a 0.04 /spl mu/m In/sub 0.5/Ga/sub 0.5/P bulk layer and a 0.06 /spl mu/m Al/sub 0.45/Ga/sub 0.55/As/GaAs digital graded superlattice (DGSL) layer. The CEHBT's exhibit a small collector-emitter offset voltage of 55 mV and a base-emitter turn-on voltage of 0.87 V, which is 0.4 V lower than that of 1.27 V of the InGaP/AlGaAs abrupt-emitter HBT. It is found that CEHBTs exhibits a current gain as high as 250 and is even enhanced to 385 when only a DGSL layer is used for passivation layer.