Direct bandgap optical transitions in Si nanocrystals

TL;DR

This paper models how quantum confinement affects the direct bandgap in silicon nanocrystals, showing a size-dependent red shift that enhances radiative recombination and explaining observed blue emissions.

Contribution

It provides a theoretical model linking quantum confinement to direct bandgap shifts and experimentally confirms the red shift of the F-band in Si nanocrystals.

Findings

Direct bandgap energy decreases with smaller nanocrystals.

Quantum confinement enhances radiative recombination.

Experimental confirmation of the red shift of the F-band.

Abstract

The effect of quantum confinement on the direct bandgap of spherical Si nanocrystals has been modelled theoretically. We conclude that the energy of the direct bandgap at the $\Gamma$-point decreases with size reduction: quantum confinement enhances radiative recombination across the direct bandgap and introduces its "red" shift for smaller grains. We postulate to identify the frequently reported efficient blue emission (F-band) from Si nanocrystals with this zero-phonon recombination. In a dedicated experiment, we confirm the "red" shift of the F-band, supporting the proposed identification.