Emitter-Resistance Effect on Cutoff Frequency of Widegap-Emitter Si HBTs

Mamoru UGAJIN  Yoshihito AMEMIYA  

IEICE TRANSACTIONS on Electronics   Vol.E74-C   No.6   pp.1609-1614
Publication Date: 1991/06/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Device and Process Simulation for Ultra Large Scale Integration)

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This paper dicusses the emitter-resistance (RE) effect on the cutoff frequency (fT) of silicon heteroemitter bipolar transistors (Si HBTs) by using two-dimensional device simulation, circuit simulation and small-signal analysis. It is shown that an approximate formula fT=fT0/(1+2πfT0RECC) agrees well with the device and circuit simulation results. The emitter resistance affects the cutoff frequency greatly. The conductance modulation in lightly-doped heteroemitter layers with a heavily-doped backup layer is also analyzed. It is found that the carrier injection from the heavily-doped backup layer into the lightly-doped heteroemitter layer reduces the emitter resistance to one-fourth the value at best. The permissible lower limit of electron mobility in heteroemitter is estimated roughly to be 2 cm2v-1s-1.