In heterojunction bipolar transistors (HBTs), the reverse base current
s flow from the outer base periphery to the collector. The reverse bas
e and collector resistances are therefore dominated by contact resista
nce, which is inversely proportional to the outer base and inner colle
ctor 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 collect
or voltage sweeps. We compare models with measurements where the base
and collector peripheries decrease with increasing emitter diameters.
(C) 1997 Elsevier Science Ltd.