Size, oxidation, and strain in small Si/SiO2 nanocrystals

TL;DR

This study investigates how size, oxidation, and strain influence the structural, electronic, and optical properties of Si/SiO2 nanocrystals, revealing the significant role of interface oxidation and strain effects on their behavior.

Contribution

It introduces a method to incorporate strain effects into electronic and optical property predictions of Si/SiO2 nanocrystals, highlighting the importance of interface oxidation degree.

Findings

Silica matrix induces strain affecting band gap values.

Quantum confinement dominates in hydrogenated nanocrystals.

Interface oxidation degree significantly influences nanocrystal properties.

Abstract

The structural, electronic and optical properties of Si nanocrystals of different size and shape, passivated with hydrogens, OH groups, or embedded in a SiO2 matrix are studied. The comparison between the embedded and free, suspended nanocrystals shows that the silica matrix produces a strain on the embedded NCs, that contributes to determine the band gap value. By including the strain on the hydroxided nanocrystals we are able to reproduce the electronic and optical properties of the full Si/SiO2 systems. Moreover we found that, while the quantum confinement dominates in the hydrogenated nanocrystals of all sizes, the behaviour of hydroxided and embedded nanocrystals strongly depends on the interface oxidation degree, in particular for diameters below 2 nm. Here, the proportion of NC atoms at the Si/SiO2 interface becomes relevant, producing surface-related states that may affect the quantum confinement appearing as inner band gap states and then drastically changing the optical response of the system.