Plasmon-induced potential fluctuation is a key limiting factor for device scaling. To evidence such fluctuation and correctly model it, we first simulated a highly doped P-N junction: Esaki tunnel diode by examining its current-voltage characteristics. Better results were obtained by comparing experimental data with the fluctuations taking into account. Then, we introduced our self-consistent Schrödinger and Poisson equation simulator in silicon two-dimensional electron gas, by adding wave-function penetration and non-parabolic corrections to ensure a more realistic modeling. More suitable surface roughness parameters were determined along with physical interpretations. Finally, we examined potential fluctuation phenomenon using our simulator to model how device performance degrades with long-range Coulomb interactions.