BASE AND COLLECTOR LEAKAGE CURRENTS OF ALGAAS/GAAS HETEROJUNCTION BIPOLAR-TRANSISTORS

Base and collector leakage currents are extremely important to AlGaAs/GaAs heterojunction bipolar transistor (HBT) dc characteristics, and a simple model to describe such currents is presented. This study suggests that these currents are originated from the electron and hole leakage through the dielectric-layer (e.g., polyimide, nitride, etc.) interface at the emitter-base and base-collector peripheries, as well as through the n+-subcollector/semi-insulating substrate interface. Five HBTs having similar intrinsic make-ups (i.e., doping concentration and layer thickness) but different extrinsic make-ups (i.e., finger pattern, perimeter, dielectric layer, etc.) are investigated, and with the aid of the model, the possible mechanisms contributing to their leakage behavior identified.