Valley-dependent 2D transport in Si-MOSFETs

TL;DR

This paper provides a theoretical analysis of 2D electronic transport in Si inversion layers, highlighting how valley degeneracy influences mobility, conductivity, and magnetoresistance, with implications for high-mobility Si(111) structures.

Contribution

It offers a comprehensive theoretical framework linking valley degeneracy to 2D transport properties in Si-MOSFETs, supported by analytical and numerical results.

Findings

Mobility increases monotonically with valley degeneracy.

Enhanced temperature and magnetic field dependence of conductivity with higher valley degeneracy.

Predictions for magnetoresistance in high-mobility Si(111) inversion layers.

Abstract

Motivated by interesting recent experimental results, we consider theoretically charged-impurity scattering-limited 2D electronic transport in (100), (110), and (111)-Si inversion layers at low temperatures and carrier densities, where screening effects are important. We show conclusively that, given the same bare Coulomb disorder, the 2D mobility for a given system increases monotonically with increasing valley degeneracy. We also show that the temperature and the parallel magnetic field dependence of the 2D conductivity is strongly enhanced by increasing valley degeneracy. We analytically consider the low temperature limit of 2D transport, particularly its theoretical dependence on valley degeneracy, comparing with our full numerical results and with the available experimental results. We make qualitative and quantitative predictions for the parallel magnetic field induced 2D magnetoresistance in recently fabricated high-mobility 6-valley Si(111)-on-vacuum inversion layers. We also provide a theory for 2D transport in ultrahigh mobility Si(111) structures recently fabricated in the laboratory, discussing the possibility of observing the fractional quantum Hall effect in such Si(111) structures.