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Computational studies of point defects in aluminium nitride

Zhu, Lei; (2022) Computational studies of point defects in aluminium nitride. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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The aim of this work is to investigate intrinsic point defects systematically in the wide band gap semiconductor material aluminium nitride (AlN) by means of computational molecular modelling techniques. Molecular mechanical (force field method) and the embedded cluster hybrid molecular quantum mechanics/molecular mechanics (QM/MM) method are the two key techniques applied in this study. By using GULP (the MM code), new 2-body and 3-body interatomic potentials for AlN are developed. A broad range of physical properties predicted through the two interatomic potentials agree well with experiment data and other theoretical results. The new interatomic potentials are applied to further investigate the lattice stability, physical properties, defect energetics and defect migration barriers of AlN. The work using the molecular mechanical tool lays the foundation of the subsequent QM/MM studies. By using Chemshell (the QM/MM interface), embedded defective AlN clusters in the QM/MM environment are treated with the density functional theory (DFT) methods with the PBE0, B97-2 and BB1K hybrid functionals to obtain the formation energies of native vacancy, interstitial, and anti-site point defects. We find nitrogen vacancy and N split interstitial are the two most favourable defects in both N-rich and N-poor conditions. Relevant diffuse states, thermodynamic concentrations, and ionization transition processes are discussed. Finally, by constructing the configuration-coordinate diagrams, we are able to assign the luminescence and absorption bands to some of defect states. The optical bands from the electron vertical processes of N vacancy and Al vacancy agree well with many previous experiment and theoretical results. The results of other types of defects also bring new insight into resolving the long-term debate around the role of defects in the material.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Computational studies of point defects in aluminium nitride
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author [year]. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
UCL > Provost and Vice Provost Offices > UCL BEAMS
URI: https://discovery.ucl.ac.uk/id/eprint/10153769
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