Verification of Multiple Mechanism Model for the Photoluminescence of Oxidized Porous Silicon and Nanosilicon Particle Embedded in Silicon Oxide
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Date
2007-07
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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
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Keywords
Mechanism Model for the Photoluminescence