Size controlled germanium nanocrystals in dielectrics : structural and optical analysis and stress evolution
Author
Bahariqushchi, Rahim
Advisor
Gülseren, Oğuz
Date
2017-09Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
Group IV semiconductor nanocrystals, namely silicon and germanium have attracted
much interest in the past two decades due to their broad applications
in photovoltaic, memory, optoelectronic, medical imaging and photodetection
devices. Generally, there are two major features of semiconducor nanocrystals:
First, spatial confinement of charge carriers which leads to the significant changes
in optical and electronic properties of materials as a function of size. This effect
gives the possibility to use the size and shape of the nanocrystals to tune the energy
of electronic energy states. Second feature of nanocrystals, is the increased
of surface area to volume ratio of the nanocrystal with reducing size. This leads
to an enhanced role of the effects related to surface and interface of the nanocrystal.
Furthermore, stress on the nanocrystals can lead modification of the band
structure as well as in
uencing the crystallization of the nanomaterials. Recent
works show that measurement and control of the stress can open the way for
strain engineering of the electronic band structure, thereby opening the way for
new physics and applications. In this thesis, we first carry out a study on the
synthesis of germanium embedded in silicon nitride and oxide matrices. In
uence
of the annealing method as well as germanium concentration on the formation of
nanocrystals is discussed. It was found that Ge concentration and annealing play
important roles in the formation of the Ge nanocrystals. With crystallographic
data obtained from high resolution transmission electron microscopy, quantitative
analysis of stress state of germanium nanocrystals have been done by analyzing
Raman peak shift of embedded nanocrystals taking into account the phonon
confinement effect. Finally, using stressors as buffer layers, superlattices of Ge
nanosheets were studied to understand the effects of the stressors on the stress
state of Ge nanocrystals. We demonstrate that it is possible to tune the stress
on the Ge nanocrystals from compressive to tensile. Finally we showed a three
dimensional Ge quantum solid that can be used in optoelectronic applications.
Keywords
Germanium NanocrystalsDielectric Matrices
Quantum Confinement Effect
Phonon Confinement Model
Phonon Raman Spectroscopy
High Resolution Transmission Electron Microscopy
Strain Engineering
Photoluminescence Spectroscopy
Superlattices