Forward delay in scaled Al0.48In0.52As/In0.53Ga0.47As heterojunction bipolar transistors

We present experimental measurements and numerical simulations of the intrinsic forward delay as a function of base thickness in abrupt junction n-p-n Al0.48In0.52As/In0.53Ga0.47As heterojunction bipolar transistors. For base thicknesses up to 1350 Å and impurity concentration p=1.5×1019 cm−3 we find that nonequilibrium electron transport ensures that base transit delay is less than that in the 3000-Å-thick collector space-charge region. This provides an opportunity to increase base thickness and reduce base resistance without sacrificing the intrinsic forward delay time.