A First-Principles Study on Bulk and Transfer Doping of Diamond
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My Ph.D. thesis is available here as a PDF file:
A First-Principles Study on Bulk and Transfer Doping of Diamond (5.9 MB, PDF).
Abstract
Presented herein are the results of theoretical investigations addressing current issues in the doping of diamond. The work has been conducted using first-principles calculations based on density-functional theory under the local-density approximation. Particular emphasis is placed upon two currently problematic aspects of doping diamond: the lack of a suitable shallow donor impurity for n-type doping of the bulk, and the need for a stable adsorbate material for p-type doping of the diamond surface (transfer doping). Since the latter clearly requires an understanding of the properties of the various diamond surfaces, the effects of atomic geometry and surface termination on the electronic structure of the technologically important diamond surfaces have also been investigated.
This study reproduces the experimentally well-known properties of nitrogen and phosphorus defects in diamond, and proceeds to predict that arsenic and antimony will be shallower donors than phosphorus, which is at present the most successful n-type dopant. However, the practicality of doping with these larger species may be hindered by the difficulty of incorporating their atoms into the diamond lattice, and by their high likelihood of becoming compensated by forming complexes with vacancies or hydrogen. Meanwhile, the controversial sulphur defect is found to be a deep donor, while the recent experimental observations of shallow-donor behaviour in deuterated, boron-doped diamond samples are not explained by any of the boron-hydrogen complexes modelled in this study. Finally, the N–Si4 shallow-donor candidate has been critically investigated.
The effects of hydrogen and oxygen termination on the diamond surface are investigated in detail, and both the structural and electronic properties are shown to agree well with experimental observations. An important distinction is made between bulk- and surface-related electronic properties, and the influence of surface states on band bending and electron emission is discussed.
Regarding p-type transfer doping of diamond, this study finds that buckminsterfullerene (C60) can effect an electron transfer from hydrogen-terminated diamond, when present in the form of one or more closely packed monolayers on the surface. This work also reports the prediction that the greater electron affinities of fluorinated fullerenes (such as C60F36) will enhance the effect, to such an extent that individual molecules may extract electrons from a diamond substrate — a finding that has been borne out in recent experiments.