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On the properties of point defects in silicon nanostructures from ab initio calculations

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Title: On the properties of point defects in silicon nanostructures from ab initio calculations
Authors: Corsetti, Fabiano
Item Type: Thesis or dissertation
Abstract: In this thesis we apply a variety of computational methods based on density-functional theory (DFT) to the study of defect centres in bulk silicon and silicon nanostructures. Firstly, we discuss the system-size convergence of point defect properties in the supercell method for deep-level defects in bulk silicon; we consider both the vacancy and gold impurity. For the vacancy, we investigate systematically the main contributions to the finite size error that lead to the well-known slow convergence with respect to system size of defect properties, and demonstrate that different properties of interest can benefit from the use of different k-point sampling schemes. We also present a simple and accurate method for calculating the potential alignment correction to the valence band maximum of charged defect supercells by using maximally-localised Wannier functions, and show that the localised view of the electronic structure provided by them gives a clear description of the nature of the electronic bonding at the defect centre. For the gold impurity, we show that the system becomes a non-spin-polarised negative-U centre due to the effect of Jahn-Teller distortion, thus providing a simple explanation for the absent electron paramagnetic resonance signal for gold in silicon. The calculated transition levels are found to be in excellent agreement with experimental measurements. We then investigate the segregation of arsenic impurities in silicon close to an interface with amorphous silica. We employ a multiscale approach, generating a realistic disordered interface structure from Monte Carlo simulation, with a continuous random network model of the system parametrised from DFT. We calculate the segregation energy using DFT for a large number of substitutional sites encompassing all the oxidation states of silicon, and show that the results can be understood with a minimal model based only on the local strain and volume of the defect site.
Content Version: Open Access
Issue Date: Feb-2012
Date Awarded: Jun-2012
URI: http://hdl.handle.net/10044/1/9754
DOI: https://doi.org/10.25560/9754
Supervisor: Mostofi, Arash
Foulkes, Matthew
Sponsor/Funder: Engineering and Physical Sciences Research Council
Department: Materials
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Materials PhD theses

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