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Optical Properties of Wide Bandgap PerovskitesAl Nasser, Hamza 07 1900 (has links)
Wide bandgap perovskites are emerging as suitable candidates for the technology of tandem solar cells. Understanding their optical properties is a prerequisite for improving the corresponding solar cells’ efficiencies. In this thesis, we employ various steady-state spectroscopies to reveal the optical properties of two wide bandgap perovskites: FA0.83Cs0.17Pb(I0.7Br0.3)3 or PVK1 and FA0.83Cs0.17Pb(I0.5Br0.5)3 or PVK2. The optical properties of interest are the semiconductors’ absorption spectra, the sub-bandgap absorption features, the bandgap energy, the Urbach energy, and the excitonic binding energy. We find that the sub-bandgap absorption can be characterized by a single exponential function. We also find that the Urbach energies and the excitonic binding energies are below the thermal energy at room temperature, which signals that PVK1 and PVK2 are excellent nominees for photovoltaic absorbers. Finally, the bandgap energy is red shifted due to excitonic effects as revealed by the Elliot model.
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Investigation Of Plasma Deposited Boron Nitride Thin FilmsAnutgan, Mustafa 01 August 2007 (has links) (PDF)
Hexagonal boron nitride (h-BN) thin films are deposited by plasma enhanced
chemical vapor deposition (PECVD). Effects of heat treatment and source gases on
the structure and physical properties are investigated. Chemical bonding is analyzed
in comparison with the better understood isoelectronic carbon compound, graphite. It
seems that the basic difference between h-BN and graphite arises from the different
electronegativities of boron and nitrogen atoms. Optical absorptions in UV-visible
range for crystalline and amorphous structures are outlined. The expressions used for
the evaluation of mechanical stress induced in thin films are derived. The deposited
films are considered to be turbostratic as they do not exhibit the characteristic optical
absorption spectra of a crystal. A new system, stylus profilometer, is implemented
and installed for thin film thickness and mechanical stress measurements. Hydrogen
atom density within the films, estimated from FTIR spectroscopy, is found to be a
major factor affecting the order and mechanical stress of the films. Heat treatment of
the films reduces the hydrogen content, does not affect the optical gap and slightly
increases the Urbach energy probably due to an increased disorder. Increasing the
nitrogen gas flow rate in the source gas results in more ordered films. The virtual
crystal of these films is detected to be unique. Relative bond concentrations of the constituent elements indicate a ternary boron-oxygen-nitrogen structure. The
physical properties of h-BN such as high resistivity and wide band gap seem suitable
for optoelectronic applications such as gate dielectrics in thin film transistors and
light emitting devices in the blue region.
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Акустические свойства неупорядоченных и наноструктурных материалов для микро- и оптоэлектроники : магистерская диссертация / Acoustic properties of disordered and nanostructured materials for micro- and optoelectronicsПеревозчикова, Ю. А., Perevozchikova, Y. A. January 2015 (has links)
Объектом исследования являются 3 образца нанокерамики на основе Al2O3, и 4 образца кварцевых стекол: КИ, КВ, КУ, КС-4В.
Цель данной работы – исследование акустических свойств, обусловленных особенностями микро- (нано)структуры двух категорий материалов микро- и оптоэлектроники – нанокерамики на основе Al2O3 и оптических кварцевых стекол.
В процессе работы были: исследованы акустические свойства материалов микро- (нанокерамика на основе Al2O3) и оптоэлектроники (кварцевые стекла), исследованы оптические параметры кварцевых стекол и установлена корреляция между акустическими и оптическими параметрами.
В результате исследования был создан оригинальный измерительный стенд и разработана методика измерения значений скоростей поперечных ультразвуковых волн, определены упругие характеристики нанокерамики на основе Al2O3 и кварцевых стекол, а также оптические параметры стекол. В данной работе удалось установить корреляцию между акустическими и оптическими параметрами. Используя измерения скоростей ультразвука и оптического поглощения, были определены фундаментальные характеристики образцов. Это способствует пониманию структурно-чувствительных свойств, а значит, в дальнейшем и влиять на них, создавая материалы с нужными параметрами для лучшей работы приборов микро- и оптоэлектроники. / Objects of research are 3 samples of nanoceramiсs based on Al2O3 and 4 samples of quartz glasses: KI, KU, KV, KS-4V.
The aim of this work is the study of the acoustic properties due to the peculiarities of micro- (nano)structures of the two categories of micro- and optoelectronics materials: nanoceramics based on Al2O3 and optical quartz glass.
The acoustic properties of materials micro- (nanoceramics based on Al2O3) and optoelectronics (quartz glass) were studied, the optical parameters of quartz glass were investigated, and a correlation between acoustic and optical parameters was found.
The original test stand and the method of measuring the transverse ultrasonic waves velocities were created, the elastic characteristics of nanoceramics based on Al2O3 and optical quartz glass and the optical parameters of glass were determine. In this paper we determined a correlation between acoustic and optical parameters. Using measurements of the velocity of ultrasound and optical absorption fundamental characteristics of the samples were determined. This contributes to an understanding of structure-sensitive properties that will help create materials with the necessary parameters for the best performance of micro- and optoelectronics.
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