Approach for determination of extrinsic resistance for equivalent circuit model of metamorphic InP/InGaAs HBTs

An improved extraction procedure for determination of the extrinsic resistances of metamorphic InP heterojunction bipolar transistors (HBTs) is presented. This method is a combination of the test structure method and an analytical method but it does not require numerical optimisation. The main advantage of this method is that the extrinsic base resistance and the collector resistance can be obtained by using cutoff mode S-parameter measurements. Bias-dependent empirical models for the intrinsic resistance and extrinsic base-collector capacitance over the whole region of operation are also presented. Good agreement is obtained between simulated and measured results for a metamorphic InP HBT with a 5 × 5 μm ² emitter in the frequency range 50 MHz-40 GHz over a wide range of bias points.