Analytical Base-Col Lector Depletion Capacitance In Vertical Sige Heterojunction Bipolar Transistors Fabricated On Cmos-Compatible Silicon On Insulator

The base-collector depletion capacitance for vertical SiGe npn heterojunction bipolar transistors (HBTs) on silicon on insulator (SOI) is split into vertical and lateral parts. This paper proposes a novel analytical depletion capacitance model of this structure for the first time. A large discrepancy is predicted when the present model is compared with the conventional depletion model, and it is shown that the capacitance decreases with the increase of the reverse collector-base bias-and shows a kink as the reverse collector-base bias reaches the effective vertical punch-through voltage while the voltage differs with the collector doping concentrations, which is consistent with measurement results. The model can be employed for a fast evaluation of the depletion capacitance of an SOI SiGe HBT and has useful applications on the design and simulation of high performance SiGe circuits and devices.