Electrical transport in two dimensional electron and hole gas on Si(001)-(2x1) surface

TL;DR

This paper investigates the electrical conductance of surface states on Si(001)-(2x1), revealing significant conduction along dimer rows and suggesting surface states dominate transport in silicon nanomembranes.

Contribution

It provides a detailed calculation of surface state conductance on Si(001)-(2x1) using extended Huckel theory and explores directional dependence and implications for silicon nanostructures.

Findings

Conductance along dimer rows is significantly higher due to orbital hybridization.

Surface conductance exceeds bulk conductance near band edges at room temperature.

Transport through surface states may dominate in silicon nanomembranes' STM measurements.

Abstract

Si(001)-(2$\times$1) surface is one of the many two-dimensional systems of scientific and applied interest. It has two surface state bands (1) anti-bonding pi* band, which has acceptor states and (2) bonding pi band, which has donor states. Due to its asymmetric dimer reconstruction, transport through this surface can be considered in two distinct directions, i.e. along and perpendicular to the paired dimer rows. We calculate the zero bias conductance of these surface states under flat-band condition and find that conduction along the dimer row direction is significant due to strong orbital hybridization. We also find that the surface conductance is orders of magnitude higher than the bulk conductance close to the band edges for the unpassivated surface at room temperature. Therefore, we propose that the transport through these surface states may be the dominant conduction mechanisms in the recently reported scanning tunneling microscopy of silicon nanomembranes. We also calculate the zero bias conductance under flat-band condition for the weakly interacting dangling bond wires along and perpendicular to the dimer row direction and find similar trends. Extended Huckel theory is used for the electronic structure calculations, which is benchmarked with the GW approximation for Si and has been successfully applied to Si systems in past.