Direct Extraction of InP/GaAsSb/InP DHBT Equivalent-Circuit Elements From $S$-Parameters Measured at Cut-Off and Normal Bias Conditions

A unique direct parameter extraction method for the small-signal equivalent-circuit model of InP/GaAsSb/InP double heterojunction bipolar transistors (DHBTs) is presented. S-parameters measured at cut-off bias are used, at first, to extract the distribution factor X0 for the base-collector capacitance at zero collector current and the collector-to-emitter overlap capacitance Cceo present in InP DHBT devices. Low-frequency S-parameters measured at normal bias conditions then allows the extraction of the external access resistances Rbx, Re, and Rcx as well as the intrinsic HBT elements of the device. The terminal inductances of the device are extracted from high frequency S-parameters by employing the intrinsic HBT elements extracted at low-frequency. Compared to other published direct parameter extraction techniques the proposed method is developed specifically for III-V based HBTs and avoids S-parameters measured at the critical open-collector bias condition. The method is applied to an 1.5 μm emitter width InP/GaAsSb/InP DHBT device and leads to excellent prediction of the measured S-parameters in the 250 MHz - 65 GHz frequency range.