Generation-recombination noise modelling in semiconductor devices through population or approximate equivalent current density fluctuations

Generation-recombination noise modelling of semiconductor devices through t he impedance field method customarily exploits, as microscopic noise source s, approximate equivalent current density fluctuations derived in a homogen eous system; moreover, such an equivalent approach often makes use of a mon opolar (majority carrier) model only, Taking, as a reference model, an accu rate numerical implementation of the Langevin approach wherein electron and hole density fluctuations are applied to a bipolar drift-diffusion physics -based model, we show that the approximate equivalent approach is inaccurat e, even in a uniformly doped sample, unless the effect of the ohmic boundar y conditions is negligible. Moreover, the monopolar equivalent model introd uces further inaccuracies whenever minority carrier fluctuations are not ne gligible; this is shown to occur not only for direct processes, but also fo r trap-assisted transitions involving deep levels in a p- or Ii-doped semic onductor. The equivalent models are finally shown to match the exact approa ch only if the carrier lifetimes and fluctuation spectra are corrected empi rically. (C) 1998 Elsevier Science Ltd. All rights reserved.