On the Interactions of Point Defects, Dopants and Light Element Impurities in Silicon as Stimulated by 200 kV Electron Irradiation.

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Title: On the Interactions of Point Defects, Dopants and Light Element Impurities in Silicon as Stimulated by 200 kV Electron Irradiation.
Author: Stoddard, Nathan Gregory
Advisors: Robert Nemanich, Committee Member
George Rozgonyi, Committee Co-Chair
Gerd Duscher, Committee Co-Chair
Nadia El-Masry, Committee Member
Phil Russell, Committee Member
Abstract: The purpose of this research has been the investigation of atomic manipulation in silicon. It has been demonstrated that bulk vacancies and interstitials are created and spatially separated one Frenkel pair at a time during 200 kV electron irradiation of nitrogen-doped silicon. The mechanism by which the nitrogen pair allows Frenkel pair separation is shown to be a combination of the lowering of the energy barrier to a knock-on event combined with a more stable end-state. Anomalous nitrogen diffusion has been observed as a result of low energy ion milling, and the diffusion of nitrogen is studied theoretically, revealing a new, low energy model for N2 pair diffusion. For the first time, 200 kV irradiation has been demonstrated not only to create Frenkel pairs during broad-beam irradiation, but also to allow the formation of extended defects like voids, oxygen precipitates and interstitial complexes. Using electron energy loss spectroscopy combined with first principles simulations, dark and bright areas induced in Z contrast images by 200 kV irradiation are demonstrated to be due to vacancy and self-interstitial complexes, respectively, with N>2. Finally, the manipulation of dopants in silicon is induced by using the difference in energy transferable from a 200 kV electron to light versus heavy elements (e.g. B vs. Sb). Atomic Force Microscopy is used to demonstrate that n-type regions with a size corresponding to the beam diameter are created in p-type material by short periods of 200 kV e-beam exposure. In this way, a method can be developed to create p-n-p type devices of arbitrary size in codoped silicon using a room temperature process.
Date: 2005-07-21
Degree: PhD
Discipline: Materials Science and Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/5392


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