A new direct method for determining the heterojunction bipolar transistor equivalent circuit model

The authors propose a novel technique for determining the small-signal equivalent circuit of a heterojunction bipolar transistor (HBT). With this technique, the parasitics are obtained independently from special test structures or measured from the transistor. Knowledge of these parasitic elements makes it possible to deembed the intrinsic HBT from the terminal measurements on the transistor and compute the intrinsic element values directly without any curve fitting. This procedure is applied to self-aligned base AlGaAs/GaAs, Npn HBTs with a base doping of 10¹⁹ cm^-3 and emitter dimensions of 2 μm×8 μm. The accurate determination of parameter values allows the device technology to be intelligently modified to optimize device performance