Atomistic simulations of self-trapped exciton formation in silicon nanostructures: The transition from quantum dots to nanowires

TL;DR

This study uses time-dependent density functional theory to analyze how electron confinement and structure length influence exciton behavior and optical spectra in silicon nanostructures, revealing size-dependent self-trapping phenomena.

Contribution

It provides a systematic investigation of electron confinement effects and exciton self-trapping in silicon nanostructures with varying aspect ratios using advanced computational methods.

Findings

Short nanorods exhibit significant Stokes shifts due to excited state relaxation.

Self-trapped excitons form only in short nanostructures, not in longer wires.

Longer nanowires show delocalized excitons with minimal geometrical distortion.

Abstract

Using an approximate time-dependent density functional theory method, we calculate the absorption and luminescence spectra for hydrogen passivated silicon nanoscale structures with large aspect ratio. The effect of electron confinement in axial and radial directions is systematically investigated. Excited state relaxation leads to significant Stokes shifts for short nanorods with lengths less than 2 nm, but has little effect on the luminescence intensity. The formation of self-trapped excitons is likewise observed for short nanostructures only; longer wires exhibit fully delocalized excitons with neglible geometrical distortion at the excited state minimum.