Quantum confinement effects and strain-induced band-gap energy shifts in core-shell Si-SiO2nanowires

Abstract

Nanowires are unique objects to explore quasi-one-dimensional electronic systems. In order to obtain quantum-confined excitons in silicon nanowires, we strongly oxidized such nanowires and obtained core-shell silicon-silicon dioxide structures. Low-temperature photoluminescence measurements were performed after each oxidation step to link the band-gap energy to the dimensions of the nanowires. Surprisingly, the electronic band gap first decreases prior to increasing at quantum dimensions (the silicon nanowires, once oxidized, are stressed by the silicon dioxide shell). The controlled nanowire oxidation allowed us to develop an empirical model to estimate the strain-induced gap energy shift. With this model, we extracted the quantum energy as a function of the diameters of smaller nanowires, and its diameter dependence is in agreement with tight-binding calculations.