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The growth and evaluation of epilayers grown by silicon molecular beam epitaxy
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Houghton, Richard F. (1991) The growth and evaluation of epilayers grown by silicon molecular beam epitaxy. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3226676~S1
Abstract
The aim of this work was to evaluate and improve the quality of epilayers grown by silicon molecular beam epitaxy [Si-MBE).
The first thorough study was carried out on substrate preparation, specifically aimed at the unique conditions that arise during MBE growth. This included both ex-situ wet chemical cleans, and by in-situ thermal desorption with the aid of Si evaporation to remove surface oxide. This enabled the development of a low thermal budget cleaning technique which ideally complemented the low growth temperatures attainable during MBE, one of the technique’s major advantages. This cleaning method consisted of ex-situ oxide removal in 2.5% HF solution, followed by in-situ thermal treatment at 700°C for 7 minutes with the aid of a 10A capping layer.
The dependence of residual doping on growth parameters, and the electrical and optical properties of residually doped epilayers were studied in detail for the first time. Knowledge of these factors is vital for the design of devices in which the carriers are separated from the ionised impurities that give rise to them. The background dopant was identified as phosphorus.
The effect or substrate temperature on chemical purity and crystalline perfection was then studied to determine the optimum temperature for growth. The presence of electrically active traps was analysed by deep level transient spectroscopy, and their concentration was found to fall to a minimum above 600°C. Conversely, crystalline perfection, as determined by a defect revealing etch, was found to increase as temperature decreased, reaching a optimum between 500° and 600°C for the growth rates available during this work.
The use of Ga and B as p-type dopants in Si-MBE was studied. The deficiencies of Ga as a dopant in MBE were explored and explained. To overcome boron’s only major weakness, its low vapour pressure, a novel elemental B coevaporation source was designed and constructed, which has now been universally adopted as the method of B coevaporation for MBE. This allows contamination free doping with an industry-standard dopant that exhibits excellent electrical properties. A new model for the incorporation enhancement seen with some dopants during the use of the technique known as potential enhanced doping (PED) is also proposed, involving the incorporation of atoms at damage sites caused by impingent Si+ ions. Computer modelling illustrated the feasibility of the hypothesis compared to secondary implantation, until now the most widely used model.
The development of the new elemental B source enabled the author to grow the first successful p-type atomic layer (delta) doped epilayers. These had considerable advantages over their n-type, Sb-doped counterparts, due to B’s more appropriate incorporation kinetics.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QC Physics | ||||
Library of Congress Subject Headings (LCSH): | Molecular beam epitaxy, Silicon crystals -- Properties, Silicon crystals -- Growth, Semiconductor doping | ||||
Official Date: | 1991 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Department of Physics | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Parker, E. H. C. | ||||
Format of File: | |||||
Extent: | 203 leaves : illustrations, charts | ||||
Language: | eng |
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