On the consistent modeling of band-gap narrowing for accurate device-level simulation of scaled SiGe HBTs

We investigate the modeling of heavy-doping induced band-gap narrowing (BGN) in scaled SiGe HBTs featuring high base doping. An inconsistency between simulation results obtained using either Boltzmann or Fermi-Dirac statistics is identified for two widely used commercial device simulators: MEDICI and DESSIS. A new approach to BGN modeling is introduced to correct this problem, and is successfully implemented in DESSIS, enabling consistency in the DC and RF characteristics simulated using either Boltzmann or Fermi-Dirac statistics in the presence of high doping. The impact of the distribution of BGN between the conduction band and the valence band on the simulated cut-off frequency versus bias current density characteristics is also addressed.