Abstract: In this paper,we investigate the importance of including recombination in the base side of the emitter-base space-charge-region(SCR) in the current continuity equation when computing the current gain in abrupt HBTs.Based on the thermionic field-diffusion model,new analytical expressions for the terminal currents are proposed.These new expressions are more accurate in predicting the performance of HBTs operating at high collector current density because of the inclusion of the recombination currents in the current continuity equation.

Key words: HBTs, thermionic-field-diffusion, recombination currents, current continuity equation