On the estimation of base transit time in AlGaAs/GaAs bipolar transistors

1 March 1987

journal article
Published by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Electron Device Letters

Vol. 8 (3) , 90-92
https://doi.org/10.1109/edl.1987.26562

Abstract

Electron diffusion across quasi-neutral p-type base regions representative of those used in n-p-n AlGaAs/GaAs/GaAs heterojunction bipolar transistors is investigated. Monte-Carlo simulation results demonstrate that for realistic base widths ≲ 1000 Å) electron transport cannot be described by Fick's Law. As a result, the conventional estimate of base transit time,\tau_{B} = W\min{B}\max{2}/2D_{n}, will produce substantial errors for base widths typical of those employed in heterojunction bipolar transistors. Estimates based on the ballistic transport of electrons across the base are shown to significantly underestimate base transit time-even for base widths substantially narrower than those presently employed.

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