One-dimensional model to analyze drain current fluctuation. Blue dots represent active As atoms. Lg*, effective gate length; σ = σs + σd, sum of the standard deviations of interatomic distances in the S/D extensions; Ss, the maximum separation between neighboring impurities in the S extension; Sd, that in the D extension; S, that in the S/D extensions. si and di are interatomic distances in the S/D extensions. The effects of the number of As dopants in the S extension (Ns), in the D extension (Nd), and in the S/D extensions (N) are also examined.