Fuzzy band structure of quantum dots by Bloch Orbital Expansion, unconventional insights into geometry-electronic structure relations

TL;DR

This paper introduces Bloch Orbital Expansion (BOE) as a novel method to analyze quantum dot electronic structures, revealing geometry-dependent orbital characteristics and core/shell band alignments.

Contribution

It demonstrates the application of BOE to transform real-space orbitals into momentum space, providing new insights into quantum dot surface effects and core/shell band structures.

Findings

Unpassivated facets produce mid-gap orbitals from bulk surface states.

Reconstructed facets lead to delocalized orbitals from superposed bulk Bloch orbitals.

BOE enables clear identification of core/shell band alignment.

Abstract

The extension of ab-initio methods like density functional theory (DFT) to quantum dot (QD) geometries has enabled researchers to explore relationships between QD surface termination and electronic structure. However, fully utilizing the data from DFT requires novel classification methods for QD orbitals. Here, we identify relationships between QD geometry and electronic structure by transforming real-space QD orbitals into momentum-space using Bloch orbital expansion (BOE), yielding a fuzzy QD band structure. Comparing with bulk band structures, we show that truncated, unpassivated facets in III-V and II-VI QDs produce mid-gap orbitals derived from bulk surface orbitals; an identification challenging in real space. QDs with reconstructed facets, however, feature delocalized orbitals formed by superposition of bulk Bloch orbitals. Moreover, we prepare for the first time atomistic core/shell QD models and by the BOE expansion we can clearly identify the core/shell band alignment not possible in real space. These findings emphasize BOE as a vital tool for connecting computational and experimental insights in nanocrystal research.