Base and collector resistances in heterojunction bipolar transistors

In heterojunction bipolar transistors (HBTs), the reverse base currents flow from the outer base periphery to the collector. The reverse base and collector resistances are therefore dominated by contact resistance, which is inversely proportional to the outer base and inner collector periphery lengths which are larger than the emitter lengths when the base and collector electrodes surround the emitter element. These resistances can be extracted from reverse Gummel (current vs V-bc with V-be = 0) and from measurements of output resistances at zero collector voltage sweeps. We compare models with measurements where the base and collector peripheries decrease with increasing emitter diameters. (C) 1997 Elsevier Science Ltd.