Coulomb Blockade in low mobility nanometer size Si:MOSFETs

TL;DR

This study explores Coulomb blockade phenomena in low mobility silicon MOSFETs at very low temperatures, revealing quantum dot formation and resonant tunneling effects that depend on device geometry and size.

Contribution

It demonstrates the formation of impurity quantum dots in Si:MOSFETs and characterizes their Coulomb blockade behavior, linking quantum dot size to channel length and conductance fluctuations.

Findings

Quantum dots form in Si:MOSFETs at G=e^{2}/h.

Coulomb blockade oscillation periodicity inversely proportional to channel length.

Variance of conductance logarithm scales with its mean.

Abstract

We investigate coherent transport in Si:MOSFETs with nominal gate lengths 50 to 100nm and various widths at very low temperature. Independent of the geometry, localized states appear when G=e^{2}/h and transport is dominated by resonant tunnelling through a single quantum dot formed by an impurity potential. We find that the typical size of the relevant impurity quantum dot is comparable to the channel length and that the periodicity of the observed Coulomb blockade oscillations is roughly inversely proportional to the channel length. The spectrum of resonances and the nonlinear I-V curves allow to measure the charging energy and the mean level energy spacing for electrons in the localized state. Furthermore, we find that in the dielectric regime, the variance var(lng) of the logarithmic conductance lng is proportional to its average value <lng> consistent with one-electron scaling models.