Semiconductor nanostructures are currently an active area of research, especially in the field of photovoltaics as they will play a major role in next generation solar devices that break the current theoretical limit for light-to-current conversion. For instance, the efficiency of the nanostructure-based solar cells can be increased due to carrier multiplication, or multiple exciton generation (MEG) process, where absorption of a single energetic photon results in the generation of several charge carriers. In order to design nanostructures with the desired properties, a detailed theoretical approach for studying photoexcited state processes is necessary. The approach developed in this work is based on many-body perturbation theory (MBPT) and the Boltzmann transport equation (BE) in combination with density functional theory (DFT) in order to compute quantum efficiency (QE). Conclusions about QE are made after studying all the major relaxation channels in a photoexcited system, such as exciton-to-biexciton decays, biexciton recombination and phonon-mediated exciton relaxation. In all calculations, excitonic effects have been included by solving the Bethe-Salpeter equation (BSE). Then, by including excitons in the MBPT calculations, the exciton-to- biexciton rates R1→2 as well as the biexciton-to-exciton rates R2→1 are computed by taking into account the singlet fission (SF) process. The methods developed here have been applied to various semiconductor nanostructures such as pristine chiral (6,2), (6,5) and (10,5) and functionalized (6,2) SWCNTs. We predict efficient MEG in the (6,2) and (6,5) SWCNTs within the solar spectrum range starting at the 2Eg energy threshold and with QE reaching ~ 1:6 at about 3Eg, where Eg is the electronic gap. Also, methods for MEG rates calculations have been improved by taking into account exciton-exciton interactions in the intermediate biexciton state, where results show a small (~ 40 meV) red-shift in the biexciton density of states. Finally, the MEG-BE technique is applied in studying charge transfer. Charge transfer has been studied in a doped silicon quantum dot (QD) - functionalized SWCNT system where it was found that an initial excitation localized on either the QD or CNT evolves into a transient CT state. / National Science Foundation (NSF CHE-1413614)

This work investigates transient optical properties of semiconductors and the underlying carrier and lattice dynamics after intense pulsed optical excitation. To this aim, the ex- perimental technique of pump-probe spectroscopic ellipsometry and the corresponding experimental setup is introduced first. The pump-probe scheme yields sub-picosecond temporal resolution while the spectroscopic ellipsometry measurement allows direct ex- cess to the complex-valued optical response, that means real and imaginary part of the dielectric function. The functionality of the experimental setup as well as technical de- tails, capabilities and limitations are discussed. First measurements are demonstrated on the prototypical wide-bandgap semiconductor ZnO and the classical semiconductors Ge, Si and InP. Furthermore, the full dielectric function tensor of optically anisotropic materials can be obtained from ellipsometry measurements, if suitable orientations of the material are measured and collectively analyzed. This capability will be demonstrated for the uniaxial material ZnO. Upon optical excitation, the transient occupation of electronic states is varied which leads to a redistribution of the spectral weight of absorption. This embodies the com- bined intricate effects of inter- and intra-band transitions, carrier scattering with the heated lattice as well as many-body effects such as band-gap renormalization, carrier screening and Pauli blocking. The contributions of these effects are disentangled by means of line-shape analysis of the dielectric function. For ZnO, we additionally find a strong influence of the polar electron-phonon interaction on the dielectric function that are framed as hot-phonon effects in the literature. They exemplify the importance of the lattice in the relaxation process of photo-excited semiconductors. The experimental dielectric functions will be compared to theoretical results from first-principles calcu- lation taking excitonic effects and the photo-excited carriers at elevated temperatures into account. The transient carrier dynamics are additionally supported by simula- tions of the transient carrier and lattice temperature. Moreover, spatial information on the transient carrier dynamics was obtained from pump-probe imaging ellipsometry on ZnO under similar excitation conditions. Here, the photo-excitation enables a delicate interplay between diffusion and ballistic propagation of the carriers, that leads to a non- homogeneous lateral carrier profile. This spatial modulation of the carrier density and subsequently the optical properties challenges the standard assumption of homogeneous lateral excitation in the analysis of pump-probe experiments.:Introduction 1 1 Measurement of transient optical properties 5 1.1 Light polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.2 Optical properties and ellipsometry . . . . . . . . . . . . . . . . . . . . . 6 1.3 Transient optical properties and time-resolved ellipsometry . . . . . . . . 7 1.4 Broadband femtosecond spectroscopic ellipsometry . . . . . . . . . . . . 10 2 Transient charge-carrier and lattice dynamics in photo-excited semicon- ductors 12 2.1 Four regimes of carrier relaxation . . . . . . . . . . . . . . . . . . . . . . 12 2.1.1 Hot-phonon effects in photo-excited wide-bandgap semiconductors 16 2.2 Effects of high carrier density on optical properties . . . . . . . . . . . . 17 2.3 Transient dielectric functions of ZnO . . . . . . . . . . . . . . . . . . . . 21 2.3.1 Ultrafast dynamics of hot charge carriers in an oxide semiconduc- tor probed by femtosecond spectroscopic ellipsometry . . . . . . . 21 2.3.2 Transient birefringence and dichroism in ZnO studied with fs-time- resolved spectroscopic ellipsometry . . . . . . . . . . . . . . . . . 22 2.3.3 Femtosecond-time-resolved imaging of the dielectric function of ZnO in the visible to near-IR spectral range . . . . . . . . . . . . 23 2.4 Transient dielectric functions of Ge, Si and InP . . . . . . . . . . . . . . 24 2.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3 Summary and outlook 29 Bibliography 32 Cumulated Publications 52 Symbols and abbreviations 54 Danksagung 56 Zusammenfassung nach §11 (4) der Promotionsordnung 58 / In dieser Arbeit werden die transienten optischen Eigenschaften von Halbleitern nach gepulster optischer Anregung und die zugrundeliegende Prozesse der Ladungsträgerund Kristallgitterdynamik untersucht. Zu diesem Zwecke wird die experimentelle Methode der femtosekunden-zeitaufgelösten spektroskopische Ellipsometrie eingeführt. Das Pump-Probe-Messschema gewährt eine zeitliche Aufösung von weniger als einer Pikosekunde während es die spektroskopischen Ellipsometrie ermöglicht, direkten Zugang zur komplex-wertigen optischen Antwortfunktion auf eine eintreffende elektromagnetische Welle das heißt Real- und Imaginärteil der dielektrischen Funktion (DF) in einem breiten Spektralbereich zu erhalten. Zu Beginn wird der Messaufbau der zeitaufgelösten spektroskopischen Ellipsometrie vorgestellt. Seine Funktionalität wird durch Untersuchungen am prototypischen weitbandlückigen Halbleiter ZnO und den klassischen Halbleitern Ge, Si und InP demonstriert. Weiterhin können richtungsund polarisationsabhängige optischen Eigenschaften bestimmt werden, wenn entsprechende Orientierungen der Probe gemessen und simultan modelliert werden. Diese Fähigkeit wird ebenfalls an ZnO demonstriert, da es aufgrund seiner hexagonalen Kristallstruktur anisotrope optische Eigenschaften aufweist. Die intensive optische Anregung der Halbleiter bewirkt eine zeitweilige Umverteilung der Besetzung der elektronischen Zustände, welche sich in einer deutlich veränderten Linienform der DF widerspiegelt. Verantwortlich dafür sind unter anderem elektronische Interund Intra-Band-Übergänge und Streuprozesse mit dem aufgeheizten Gitter sowie verschiedene Vielteilcheneffekte wie Bandlückrenormierung, Abschirmung der Ladungsträger und das Pauli-Prinzip. Die Beiträge dieser Effekte können mittels geeigneter Linienformanalyse der DF näher untersucht werden. Am Beispiel von ZnO wird auch die starke Wechselwirkung der Elektronen mit dem aufgeheizten Gitter und deren Auswirkungen auf die DF gezeigt. Die experimentelle DF wird mit theoretischen Berechnungen verglichen, wobei bei exzitonische Effekte und die hohe Überschussenergie der Ladungsträger berücksichtigt werden. Zusätzlich erklären Simulationen der transienten Ladungsträgerund Gittertemperatur den Verlauf der Relaxation der Ladungsträger. Weiterhin werden Information über die räumliche Ausbreitung der Ladungsträger nach optischer Anregung mittels abbildender zeitaufgelöster Ellipsometrie an ZnO gewonnen. Hierbei wird ein komplexes Zwischenspiel zwischen Diffusion und ballistischer Propagation der Ladungsträger beobachtet, welches zu einer ringförmigen Verteilung der Ladungsträger führt.:Introduction 1 1 Measurement of transient optical properties 5 1.1 Light polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.2 Optical properties and ellipsometry . . . . . . . . . . . . . . . . . . . . . 6 1.3 Transient optical properties and time-resolved ellipsometry . . . . . . . . 7 1.4 Broadband femtosecond spectroscopic ellipsometry . . . . . . . . . . . . 10 2 Transient charge-carrier and lattice dynamics in photo-excited semicon- ductors 12 2.1 Four regimes of carrier relaxation . . . . . . . . . . . . . . . . . . . . . . 12 2.1.1 Hot-phonon effects in photo-excited wide-bandgap semiconductors 16 2.2 Effects of high carrier density on optical properties . . . . . . . . . . . . 17 2.3 Transient dielectric functions of ZnO . . . . . . . . . . . . . . . . . . . . 21 2.3.1 Ultrafast dynamics of hot charge carriers in an oxide semiconduc- tor probed by femtosecond spectroscopic ellipsometry . . . . . . . 21 2.3.2 Transient birefringence and dichroism in ZnO studied with fs-time- resolved spectroscopic ellipsometry . . . . . . . . . . . . . . . . . 22 2.3.3 Femtosecond-time-resolved imaging of the dielectric function of ZnO in the visible to near-IR spectral range . . . . . . . . . . . . 23 2.4 Transient dielectric functions of Ge, Si and InP . . . . . . . . . . . . . . 24 2.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3 Summary and outlook 29 Bibliography 32 Cumulated Publications 52 Symbols and abbreviations 54 Danksagung 56 Zusammenfassung nach §11 (4) der Promotionsordnung 58

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第21315号 / エネ博第371号 / 新制||エネ||73(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー応用科学専攻 / (主査)教授 松田 一成, 教授 佐川 尚, 教授 大垣 英明 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

There is currently a great interest to develop and market organic electronic devices, and theoretical models are needed to provide physical insight and quality predictions when designing these materials. Many organic molecules absorb in the UV-vis region of light, and therefore, UV-vis spectroscopy is a relatively simple tool that can help experimentalists "see" the packing arrangements of the molecules within each material, as long as there is a solid theoretical understanding of the photophysics that links the interactions between molecules to changes in optical features. For example, the Kasha spectral shifts have been used for decades to identify J-aggregate and H-aggregate packing arrangements from red- and blue- spectral shifts, respectively. The innate presence of vibronic coupling in organic molecules gives rise to a unique set of additional spectral signatures that are far more reliable than the Kasha spectral shifts for inferring packing arrangements. Moreover, the Kasha shifts are based entirely on Coulomb coupling between molecules, which leads to the creation of delocalized Frenkel excitons. For many π-conjugated organic molecules, however, dispersion forces in π-conjugated chromophores encourage close packing distances of about 3.5-4 Å between organic monomers, which further introduces intermolecular couplings beyond the Coulomb coupling, due to intermolecular charge transfer (CT). Therefore, much theoretical research has focused on incorporating all these effects through a Frenkel-CT-Holstein Hamiltonian, in order to better understand how different packing arrangements within a given material can be identified through specific changes in steady-state absorption and photoluminescence features. In this thesis, the Frenkel-CT-Holstein model is specifically applied to study the absorption and photoluminescent spectra of various derivatives of perylene diimide (PDI), which are of great interest as non-fullerene acceptors in organic photovoltaic design. PDIs display a plethora of packing arrangements and corresponding spectral signatures just by varying the substituents within the PDI core. This thesis first aims to understand the exciton band structure of two different PDI micro-crystals that both experience similar Frenkel-CT interference, but with one system displaying dominant Coulomb interactions while the other undergoes dominant Frenkel-CT coupling. Both are close to what is called a “null”-point, and the work in this thesis explores the photoluminescent signature as a reliable means to track which side of the “null”-point the Frenkel-CT interference lies. While the Frenkel-CT-Holstein model is successful in modeling mostly absorption spectra of aggregates composed of PDI monomers, one challenge has been that aggregates of PDIs often exhibit so-called excimer features in their photoluminescence spectra, which the model cannot account for. Systems that emit broad, structureless and red-shifted excimer peaks typically display inefficient exciton transport in organic semiconductors. The bulk of this thesis has been to expand the model to account for excimer emission, which is made possible by utilizing a Holstein-Peierls (HP) Hamiltonian that incorporates the effects of both local vibronic coupling and nonlocal Frenkel-CT coupling to intermolecular motions within a dimer. The experimental spectra for two different PDI dimer systems that display different excimer features is successfully reproduced with the new theory. This thesis concludes by analyzing how nonlocal coupling, which account for changes in the Frenkel-CT mixing along an intermolecular vibrational mode, can lead to various types of excimers. Different phase relations within the electron and hole nonlocal coupling parameters can combine with different phase relations within the electron and hole Frenkel-CT coupling parameters, leading to a rich array of excimer properties, especially when combined with the additional effects of Coulomb coupling, as well as local intermolecular vibronic coupling, which can either enhance or diminish the excimer photoluminescence. Overall, the Holstein-Peierls approach offers insight into the roles of Frenkel and CT excitons in excimer formation, and highlights the importance of the magnitude and phase of the intermolecular electron and hole transfer integrals in the ground and excited state geometries in producing distinct excimer features. The model provides further insight into the origin of excimers, which lays a foundation for future theoretical and experimental studies in designing organic materials. / Chemistry

<p>Cuprous oxide (Cu₂O) has recently been proposed as a promising solid-state host for ex-<br> citonic Rydberg states with large principal quantum numbers (n) whose exaggerated wave-<br> function sizes (∝ n²) facilitate gigantic, resonant dipole-dipole (∝ n⁴) and van der Waals<br> (∝ n¹¹) interactions, making them an ideal basis for solid-state Rydberg physics and quan-<br> tum technology. Synthetic, thin-film Cu₂O samples are of particular interest because they<br> can be made defect-free via carefully controlled fabrication and are, in principle, suitable<br> for the observation of extreme single-photon nonlinearities caused by Rydberg blockade. In<br> this work, we present the development of a spectroscopy experiment for characterizing the<br> behavior of Rydberg excitons and use it to study a synthetic thin film of Cu₂O grown on a<br> transparent substrate. We present evidence for the presence of states up to n = 8 and conduct<br> the first temperature-dependent study of Rydberg excitons in a thin film. We also propose<br> a technique for studying Rydberg-Rydberg interactions via the creation of high exciton den-<br> sities and establish a set of rate equations for modeling the processes by which excitons are<br> created, interact with each other, and decay. Finally, we conclude with a discussion of the<br> project’s outlook, as well as what future work will be undertaken to study the interactions<br> between Rydberg excitons and utilize them in scalable, integrable, Rydberg-based quantum<br> devices.<br> </p>

No description available.

No description available.

Covalent SP3-hybridization defects in single-walled carbon nanotubes (CNTs) have been prevalent in recent experimental and theoretical studies for their interesting photophysical properties. These systems are able to act as excellent sources of single, infrared photons, even at room temperature, making them marketable for applications to sensing, telecommunications, and quantum information. This work was motivated by recent experimental studies on controllable defect placement and concentration as well as investigating carrier multiplication (CM) using DFT-based many-body perturbation theory (MBPT) methods to describe excitonic relaxation processes. We find that pristine CNTs do not yield appreciable MEG at the minimum threshold of twice the optical gap 2Eg, but covalent functionalization allows for improved MEG at the threshold. Finally, we see that defect-defect interactions within CNT systems can be modeled simply as HJ-aggregates in an effective Hamiltonian model, which is shown to be valid for certain, highly-redshifted defect configurations at low defect-defect separation lengths.

We report on the investigation and observation of Bloch surface wave polaritons, resulting from the interaction between excitons in ZnO and a Bloch surface wave supported by a distributed Bragg reflector (DBR), for temperatures up to 430 K. The samples were fabricated using pulsed laser deposition and consist of a DBR made of 6.5 layer pairs of yttrica-stabilized zirconia and Al2O3 with a ZnO surface layer. We measured the reflectivity of transverse electric modes using a SiO2 prism in Kretschmann–Raether configuration, giving access to high in-plane momenta. Whereas the lower polariton branch was clearly observable, the upper polariton branch was not visible, due to the strong absorption in ZnO above the excitonic resonance. By employing a coupled oscillator model for the interaction between the bare surface mode and exciton, we derived a corresponding Rabi splitting between 100–192 meV at 294 K, which decreases with increasing temperature.

In dieser Arbeit werden Untersuchungen an dem transparenten p-Typ-Halbleiter Kupferiodid (CuI) und den ternären Verbindungshalbleitern CuBrxI1-x und AgxCu1-xI vorgestellt. Im ersten Teil der Arbeit liegt der Fokus auf der Untersuchung der dielektrischen Funktion und der optischen Übergänge dieser Materialien. Basierend auf der Kombination von experimentellen Daten und theoretischen Bandstrukturrechnungen werden die beobachteten optischen Übergänge bestimmten elektronischen Übergängen in der Brillouin-Zone zugeordnet. Die optischen Eigenschaften der ternären Legierungen CuBrxI1-x und AgxCu1-xI , insbesondere die exzitonischen Übergangsenergien am Γ-Punkt werden präsentiert. Es wird gezeigt, dass die Bandlückenenergie beider Legierungen ein nichtlineares Verhalten als Funktion der Legierungszusammensetzung aufweist, welches bei tiefen Temperaturen durch einen quadratischen Krümmungsparameter im Bereich von 0.49 eV bis 0.54 eV beschrieben werden kann. Der Ursprung des beobachteten Krümmungsverhaltens wird im Hinblick auf verschiedene Beiträge wie Bindungslängenänderungen und Ladungsumverteilungseffekte diskutiert. Der Einfluss der Legierungszusammensetzung auf die Spin-Bahn-Aufspaltung wird diskutiert, wodurch Rückschlüsse auf die p-d-Hybridisierung der obersten Valenzbänder am Γ-Punkt ermöglicht werden. Es wird gezeigt, dass der Beitrag der metallischen d-Orbitale zum Valenzbandmaximum mit steigendem Br-Gehalt zunimmt, während mit steigendem Ag-Gehalt das Gegenteil der Fall ist. Des Weiteren wird die Temperaturabhängigkeit der Bandlücke für AgxCu1-xI Legierungen in Abhängkeit der Legierungszusammensetzung präsentiert. Es wird gezeigt, dass die Temperaturabhängigkeit der Bandlückenenergie mit steigendem Ag-Gehalt abnimmt, was hauptsächlich auf die Änderung des Beitrags der thermischen Gitterausdehnung zurückzuführen ist. Im zweiten Teil dieser Arbeit werden die bandkantennahen Emissionseigenschaften von CuI Einkristallen vorgestellt. Die Ergebnisse unterstreichen die Notwendigkeit, Exziton-Polariton-Effekte bei der Interpretation der spektralen Linienform der Emissionsspektren und ihrer zeitlichen Entwicklung nach optischer Anregung zu berücksichtigen. Das unterschiedliche transiente Emissionsverhalten der freien und gebundenen Zustände wird durch deren gekoppelte Wechselwirkung erklärt, was eine Abschätzung der Defektdichte im Material ermöglicht. Die Zunahme der Lebensdauer der freien Exziton-Polaritonen mit steigender Temperatur bis etwa 150K deutet auf eine vorwiegend strahlende Rekombination in diesem Temperaturbereich hin, während die Abnahme der Zerfallszeiten bei noch höheren Temperaturen auf eine Zunahme der nicht-strahlenden Rekombinationskanäle hindeutet.:I Introduction 1 II Basics of the Cumulative Part 7 1 Physical properties and concepts . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.1 Copper and silver halides . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.2 Dielectric function . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 1.3 Exciton-polaritons in semiconductors . . . . . . . . . . . . . . . . . . 17 2 Experimental and computational techniques . . . . . . . . . . . . . . . . . . 21 2.1 Sample preparation techniques . . . . . . . . . . . . . . . . . . . . . . 21 2.2 Structural and electrical characterization . . . . . . . . . . . . . . . . 24 2.3 Optical spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 2.4 Density functional theory . . . . . . . . . . . . . . . . . . . . . . . . . 33 III Cumulative Part 35 [C1] Dielectric function of CuBrxI1-x alloy thin films . . . . . . . . . . . . . . . . . 37 [C2] Epitaxial growth of AgxCu1-xI on Al2O3 (0001) . . . . . . . . . . . . . . . . . 56 [C3] Optical properties of AgxCu1-xI alloy thin films . . . . . . . . . . . . . . . . . 64 [C4] Dynamics of exciton-polariton emission in CuI . . . . . . . . . . . . . . . . . 81 IV Summary and Outlook 95 V Publications 101 1 Publications in the basics of the cumulative part . . . . . . . . . . . . . . . . 103 2 Publications forming the cumulative part with contribution by the author . . 119 3 Further publications with contribution by the author . . . . . . . . . . . . . . 120 List of Abbreviations 121 Author Contributions 123 Zusammenfassung nach §11 (4) der Promotionsordnung der Fakultät für Physik und Geowissenschaften der Universität Leipzig 129 / The present work presents investigations on the transparent p-type semiconductor copper iodide (CuI) and the related ternary compound semiconductors CuBrxI1-x and AgxCu1-xI . The first part of the thesis focuses on the study of the dielectric function and related optical transitions of this family of materials. Based on the combination of the experimental data and first principles band structure calculations the observed optical transitions are assigned to specific electronic transitions in the Brillouin zone. The optical properties of ternary CuBrxI1-x and AgxCu1-xI alloys and in particular the excitonic transition energies at the Γ-point as a function of the alloy composition are discussed in detail. It is shown that the bandgap energy of both alloys exhibits non-linear behavior as a function of alloy composition, which can be described by a quadratic bowing parameter in the range of 0.49 eV and 0.54 eV at low temperatures. The origin of the observed bowing behavior is discussed in terms of various physical and chemical contributions, such as changes in bond lengths and charge redistribution effects. The influence of the alloy composition on the spin-orbit splitting energy Δ0 is also discussed in detail, allowing conclusions to be draw down about the p-d hybridization of the top valence bands at the Γ-point. It is shown that the contribution of the metal d orbitals to the valence band maximum increases with increasing Br-content, while the opposite is true for increasing Ag incorporation. In addition to the transition energies at low temperatures, the temperature dependence of the bandgap for AgxCu1-xI alloys as a function of alloy composition is presented. It is shown that the temperature dependent energy shift of the bandgap decreases with increasing Ag content, which is mainly due to the change in the contribution of lattice thermal expansion. In the second part of this work, the properties of the near-band edge emission of CuI single crystals are presented. The obtained results highlight the importance of considering the exciton-polariton effects when interpreting the spectral line shape of the emission peaks as well as their temporal behavior after an optical excitation. The different transient decay characteristics of the free and bound states are explained by their coupled interaction, allowing an approximation of the defect density in the material. With increasing temperature, an increase in the lifetime of the free exciton polaritons was observed up to ca. 150K, indicating mainly radiative recombination in this temperature range. The observed decrease in the decay time at higher temperatures indicates a rapid increase in non-radiative recombination channels.:I Introduction 1 II Basics of the Cumulative Part 7 1 Physical properties and concepts . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.1 Copper and silver halides . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.2 Dielectric function . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 1.3 Exciton-polaritons in semiconductors . . . . . . . . . . . . . . . . . . 17 2 Experimental and computational techniques . . . . . . . . . . . . . . . . . . 21 2.1 Sample preparation techniques . . . . . . . . . . . . . . . . . . . . . . 21 2.2 Structural and electrical characterization . . . . . . . . . . . . . . . . 24 2.3 Optical spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 2.4 Density functional theory . . . . . . . . . . . . . . . . . . . . . . . . . 33 III Cumulative Part 35 [C1] Dielectric function of CuBrxI1-x alloy thin films . . . . . . . . . . . . . . . . . 37 [C2] Epitaxial growth of AgxCu1-xI on Al2O3 (0001) . . . . . . . . . . . . . . . . . 56 [C3] Optical properties of AgxCu1-xI alloy thin films . . . . . . . . . . . . . . . . . 64 [C4] Dynamics of exciton-polariton emission in CuI . . . . . . . . . . . . . . . . . 81 IV Summary and Outlook 95 V Publications 101 1 Publications in the basics of the cumulative part . . . . . . . . . . . . . . . . 103 2 Publications forming the cumulative part with contribution by the author . . 119 3 Further publications with contribution by the author . . . . . . . . . . . . . . 120 List of Abbreviations 121 Author Contributions 123 Zusammenfassung nach §11 (4) der Promotionsordnung der Fakultät für Physik und Geowissenschaften der Universität Leipzig 129