ANALYSIS OF THE EMITTER-DOWN CONFIGURATION OF DOUBLE-HETEROJUNCTION BIPOLAR-TRANSISTOR

A two-dimensional numerical study of the parasitic effects on current gain-beta and cutoff frequency f(T) of the emitter-down configuration of AlGaAs/GaAs double-heterojunction bipolar transistors (DHBT's) is reported. The studied structures include: those with and without the extrinsic emitter regions, a structure with oxygen implantation in the extrinsic emitter region, and two structures with P+ dopant implantation of 1000 and 300 angstrom into the extrinsic emitter region. Analysis of the structures with and without the extrinsic emitter region shows that parasitic effects associated with the extrinsic emitter seriously degrade beta and f(T), and lead to an extremely asymmetric operation of the DHBT's. The three structures with the extrinsic emitter region modified by the implantations all exhibit improved beta and f(T) at low bias. However, the effectivenesses of the implant approaches to minimize the parasitics are quite different and are analyzed in this work.