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Title:Optical properties of size selected nanocrystallites in porous silicon
Author(s):Yamani, Zain Hassan
Doctoral Committee Chair(s):Nayfeh, Munir H.
Department / Program:Physics
Subject(s):porous silicon nanocrystallites
dimer model
Abstract:The work in this thesis concentrated on processing and diagnosing porous silicon nanocrystallites that have novel chemical, structural and photoluminescent properties. FTIR and Auger electron spectroscopy showed that while conventional porous films have incomplete hydrogen passivation and tend to be plagued with defects that compete with radiative channels, our "ideal" porous silicon samples are highly passivated and defect free. SEM micrographs showed that crystallite sizes in the ideal porous films are smaller than that prepared by conventional methods. Ideal porous silicon films were found to have a crystallite size gradient along the length of the sample, and appeared (under UV illumination) reddish, orangish, yellowish and greenish as the meniscus was approached. We also presented the results of size selected microsecond lifetime measurements for different emission colors. Our study showed that the decay rate depends on wavelength of emission but is quite insensitive to crystallite size. Reflectivity measurements on ideal porous silicon samples showed nonbulk- like behavior. A reflectivity study involving copper plating, however, provided evidence that the loss of crystalline absorption in the porous films is probably not due to a permanent loss in crystalline structure. Ill We have studied the theoretical photoluminescence predictions of the dimer model. There is a dramatic enhancement in the fluorescence efficiency for sizes below a critical size of 1.4 nm, the size for which the radiative states become stable against tunneling and thermal activation. The fluorescence exhibits a large Stokes shift due to the expansion of the dimers. The emission bandwidth (even for a single crystallite) is found to be quite wide especially for the ultra small crystallites where it encompasses nearly all of the visible spectrum and the near infrared. Our emission, excitation and reflectivity results support the predictions of the dimer model. However, sufficient calculated lifetime predictions are currently unavailable to confirm or reject the measured lifetime results.
Issue Date:1999
Genre:Dissertation / Thesis
Other Identifier(s):4247379
Rights Information:©1999 Yamani
Date Available in IDEALS:2012-05-29

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