The theoretical DFT study of electronic structure of thin Si/SiO2 quantum nanodots and nanowires

TL;DR

This study uses theoretical methods to analyze the electronic structures of thin silicon/silica quantum nanodots and nanowires, revealing size-dependent electronic properties and bandgap behavior relevant to nanostructure photoluminescence.

Contribution

It provides a detailed theoretical analysis of the electronic structure of silicon/silica nanostructures, highlighting size effects and the influence of surface oxidation on electronic properties.

Findings

Small silicon quantum dots have TDOS similar to bulk silicon.

Elongated nanodots and nanowires exhibit metallic behavior.

Surface oxidation opens a bandgap in the nanostructures.

Abstract

The atomic and electronic structure of a set of proposed thin (1.6 nm in diameter) silicon/silica quantum nanodots and nanowires with narrow interface, as well as parent metastable silicon structures (1.2 nm in diameter), was studied in cluster and PBC approaches using B3LYP/6-31G* and PW PP LDA approximations. The total density of states (TDOS) of the smallest quasispherical silicon quantum dot (Si85) corresponds well to the TDOS of the bulk silicon. The elongated silicon nanodots and 1D nanowires demonstrate the metallic nature of the electronic structure. The surface oxidized layer opens the bandgap in the TDOS of the Si/SiO2 species. The top of the valence band and the bottom of conductivity band of the particles are formed by the silicon core derived states. The energy width of the bandgap is determined by the length of the Si/SiO2 clusters and demonstrates inverse dependence upon the size of the nanostructures. The theoretical data describes the size confinement effect in photoluminescence spectra of the silica embedded nanocrystalline silicon with high accuracy.