Development of HBT structure to minimize parasitic elements

Abstract

Several approaches to decrease the parasitic base-emitter and base-collector capacitances, and parasitic extrinsic base resistance, of III–V HBTs are reviewed. Base-emitter depletion capacitance reduction is achieved through modifications of the epitaxial layer structure to reduce doping in the emitter. A doping dipole is introduced in order to compensate for effects of conduction band offset that can adversely affect current gain and transconductance in AlGaAs GaAs HBTs. Base-collector capacitance reduction is achieved with compensating implants of hydrogen and helium into the collector and subcollector regions (through the base layer), which decrease the extrinsic portion of the capacitance to a fringe component. Finally, to reduce extrinsic base resistance and to allow base-emitter capacitance reduction, a new structure is presented that allows HBT lateral scaling without excessive emitter edge recombination. This structure is based on multiple epitaxial growths, using GaInP, GaAs and InGaAs selective-area regrowth in the emitter region of the HBT. Concepts and initial experimental results for these approaches are discussed.