Models for Investigation of Electroluminescence from Silicon and Germanium Nanostructures
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Date
2009-06
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Addis Ababa University
Abstract
Bulk silicon (Si) and germanium (Ge) have an indirect band gap transitions; however
when they are miniaturized to nanometeric scale, the energy gap between the highest
occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO)
increases, and hence the transition changes to direct due to confinement. The HOMOLUMO
gap determines the excitation of electrons so that the nanostructures will emit
light.
In this thesis, quantum confinement effects for Si and Ge, some methods of calculating
band structures, comparative analysis of photoluminescence (PL) and electroluminescence
(EL) are presented. The thesis focuses on EL and for comparison purpose, some studies
on PL is touched. Both are the emission of energy in the form of light spectrum of different
wavelength by optical radiation, and current or strong electric field.
The dependence of EL on different parameters like size of the nanocluster, applied
voltage, band gap energy, wavelength, temperature, and time for Si are briefly examined.
The dielectric matrix silicon dioxide has unique optical and electrical properties, as a
result the dependence of EL intensity on the above parameters for Si-terminated with
oxygen and hydrogen is included in the thesis; in fact passivation enhances EL and highly
efficient EL is obtained at low operating voltages (< 6V ), it is also observed that EL
degrades with time. The EL and PL intensities occur at the same energy, however the
EL intensity has sharp Gaussian peak and red shifted compared to the PL intensity. To
get our result, we used the idea of quantum confinement model (QCM) and surface state
model (SSM), that can explain PL and EL on pure Si nanostructures, and Si-terminated
with impurities. Our results are consistent with experimental reports.
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Acknowledgements
I am grateful to my advisor, Dr. S. K. Ghoshal for his critical and constructive suggestion,
well planned follow up, constant support, and friendly approach during this research, he
was tireless, programmed, and ready to encourage me at any time when I consult him
not only in my thesis work but also in my entire graduate study. As an advisor he put a
lot of impression on me that I never forget whenever and wherever in my academic life;
I want to forward my gratitude to Mr. Anteneh Getachew and Mr. Billilign Tsigie for
their unreserved academical and technical support; with out the help of these persons the
work could not be completed duly.
I am indebted to express my heart felt gratitude to the following individuals, who have
been electronic communications with me for providing journals and other materials related
to my thesis; Mr. Ayesheshim Kebie from Alberta University, Canada, Dr. Asdesach
Zenamarkos from Germany, Mr.Getasew Admasu from Antwerp University, Belgium and
Mr. Semere Ayalew from Jimma University.
I want to express my due appreciation to Addis Ababa University, physics department,
for providing this chance, rendering good office service during my stay, and I want to
extend my acknowledgement to the staff members of the department, who devote their
time for academic matters that made my stay very happy in the graduate program.
Finally, with no words for me to express my heart feeling for his patience, I would
deeply like to thank Mr. Solomon H/M, for his great cooperation on conducting many
of my affairs directly or indirectly related to Jimma University on behalf of me and I
want to extend my gratitude to Jimma University, providing sponsorship, for faculty of
education, and Physics department for creating conducive situations to get sponsorship
from the University to my study
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Keywords
Silicon and Germanium Nanostructures