Disorder-free localization around the conduction band edge of crossing and kinked silicon nanowires

TL;DR

This study investigates ballistic quantum transport in crossing and kinked silicon nanowires, revealing a conduction band tail caused by wave reflections at junctions, independent of atomic disorder.

Contribution

It demonstrates that conduction band tails in silicon nanowires arise from wave effects at junctions, not from oxide interface disorder, using large-scale pseudopotential and transport analysis.

Findings

Ballistic transport edge is tens to hundreds of meV above the LUMO.

Localized states are silicon-derived, not oxide interface related.

Wave reflections at junctions cause conduction band tails.

Abstract

We explore ballistic regime quantum transport characteristics of oxide-embedded crossing and kinked silicon nanowires (NWs) within a large-scale empirical pseudopotential electronic structure framework, coupled to the Kubo-Greenwood transport analysis. A real-space wave function study is undertaken and the outcomes are interpreted together with the findings of ballistic transport calculations. This reveals that ballistic transport edge lies tens to hundreds of millielectron volts above the lowest unoccupied molecular orbital, with a substantial number of localized states appearing in between, as well as above the former. We show that these localized states are not due to the oxide interface, but rather core silicon-derived. They manifest the wave nature of electrons brought to foreground by the reflections originating from NW junctions and bends. Hence, we show that the crossings and kinks of even ultraclean Si NWs possess a conduction band tail without a recourse to atomistic disorder.