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Please use this identifier to cite or link to this item: http://hdl.handle.net/123456789/218

Authors: Wondwosen, Tilahun
Advisors: Dr. Sib Krishna Ghoshal
Copyright: 2007
Date Added: 9-Nov-2007
Publisher: Addis Ababa University
Abstract: The purpose of this thesis is to give a coherent explanation of the most debatable issue of highly efficient photoluminescence (PL) in the visible range found in oxidized porous Silicon (p-Si). In order to describe the PL mechanism, we considered three competitive processes, process (A) where in both photoexcitation and photoemission occur in the NSP, (B), in which photexcitation occurs in the NSP and photemission occurs in luminescence centers (LCs), in the Si-oxide layer surrounding the NSP, and (C) in which both photoexcitation and photoemission occur in the LCs. We used the first two processes to explain the optical process by the quantum confinement (QC) and quantum confinement luminescence center (QCLC) models. For the nanoscale Si/SiO2 systems, the radiative recombination rates of processes A and B are compared qualitatively. Process that plays the major role in the PL is determined by the capture cross-section, the luminescence efficiency, and the density of the LCs and size of the NSPs, all of which are dependent on the oxidation degree of the p-Si sample. For a nanoscale Si/Si-oxide system with the LC having certain capture cross-section and luminescence efficiency, it is found that the higher the LC density and the larger the size of the NSPs, the more beneficial for the QCLCM process to surpass the QCM process and vise versa. For certain LC parameters, there is a critical most probable size of the NSPs. In case when the most probable size of the NSPs is larger than the critical one, the QCLCM process dominates the PL on the other hand if the most probable size of the NSPs is smaller than the critical one, the QCM process dominates the PL. Furthermore, if the most probable size is close to the critical one both processes should be taken in to account. In general, for a p-Si sample free from oxidation, the QCM process dominates and the model is important to describe the PL. For most oxidized p-Si, the QCLCM process dominates and the model is useful to describe the PL and when the NSPs in oxidized p-Si samples have very small density or very large size, the process that both photexcitation and photoemission occur in the LCs in the silicon-oxide layer dominating. Hence, the importance of more than one type of mechanism models to describe the PL from oxidized p-Si and NSP embedded in Si-oxide is verified.
Description: A Thesis Submitted to the School of Graduate Studies of Addis Ababa University In Partial Fulfillment of the Requirements for the Degree Of Masters of Science in Physics
URI: http://hdl.handle.net/123456789/218
Appears in:Thesis - Physics

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