First principles simulations of the structure and incorporation of point defects in diamond

Abstract

Diamond is a radiation hard, a wide band-gap semiconductor, with high intrinsic carrier mobilities and high thermal-conductivity, allowing it to be used in extreme radiation environments, high temperatures and high power electronic devices. Additionally, based upon key defects, diamond has also recently emerged as a candidate material for a range of quantum-based applications including quantum information, single photon sources and high-sensitivity magnetometry. Importantly, the growth of diamond both in bulk and film form, has also radically improved over the past decade, so that use of high-quality diamond in a wide range of application is becoming more viable. Diamond synthesis, especially in the context of this thesis from the gas phase via chemical vapour deposition, is only partially understood. The defects which are incorporated during synthesis are specific to the growth method, and some key defects exhibit orientational polarisation relative to the growth surface orientation. Both the structure and polarisation of these defects are key witnesses to the growth mechanisms, and therefore developing atomistic structures is a key step towards a more comprehensive growth model. In this thesis, quantum chemical methods based upon density functional theory are used to determine the structure and incorporation mechanisms for key defect centres. It is crucial that quantum-mechanically based methods are used to provide both sufficient quantitative accuracy and to obtain the electronic properties key to comparison with the relevant experimental data, such as required for electron paramagnetic resonance centres including substitutional and interstitial nitrogen, nitrogen-vacancy and nitrogen-vacancy-hydrogen, and silicon containing centres. For the interstitial centres, it is shown that the models proposed from interpretation of the experimental data for the WAR9 and WAR10 centres are most probably incorrect, as is that of the WAR2 hydrogen-related centre. In contrast, the structures of the P1 epr centre, as well as the NV, NVH and SiV centres are not in dispute, but by simulating these centres in the upper most layers of (110), (111) and (001) diamond surfaces it is shown here that experimentally observed 100% polarisation of the N-related centres, and partial polarisation of the SiV complex can be explained for the (110) surface. The polarisation of defects can give information about how the defects incorporated during diamond growth, which in turn gives some indication of diamond growth mechanisms.