Optical studies of AlN and GaO based nanostructures using Mueller matrix spectroscopic ellipsometry
Abstract: This thesis explores the diverse optical properties manifested when light interacts with various materials, with an emphasis on circular polarization- and bandgaprelated phenomena. The studies in this work are centered around Mueller matrix spectroscopic ellipsometry, with the objective of synthesizing and characterizing nanostructured and high-quality thin films to expand our understanding of the optical properties arising from their underlying structure and electronic transitions, respectively.Papers I, II, and III of the research address the optical properties associated with circular polarization, emphasizing the importance of the morphology and structure of the sculptured thin films used. To clarify this, AlN-based chiral sculptured thin films are synthesized using glancing angle deposition and magnetron sputtering. The discussion explores the impact of different growth parameters on the morphology and crystal structure of the films. By examining these thin film samples, it is shown how their structure and crystallographic orientation can be designed to reflect narrow spectral bands of circularly polarized light at specific wavelengths. The research also tackles how thin films preferentially reflect one handedness of circularly polarized light over the other with a high degree of circular polarization. A combination of theoretical and experimental studies offers insights into the nuances of growth and light-material interactions, particularly in complex photonic structures.Papers IV and V investigate the optical properties that arise from electronic transitions in thin films, focusing on the complex dielectric function and optical bandgap phenomena. These properties are explored using high-quality single crystalline homogenous thin films of ZnGaO, grown using metal-organic chemical vapor deposition. Various formalisms to calculate bandgap values are evaluated for their precision and applicability. The modified Cody formalism stands out as the preferred choice due to its ability to provide the most linear region for extrapolating bandgap energy values. Through both theoretical calculations and experiments, a critical analysis is provided on the evolution of the crystal structure and optical properties of these thin films when exposed to elevated temperatures. These findings explain the interplay between the structural characteristics of thin films and their subsequent influence on bandgap properties.Altogether, this thesis provides a fundamental understanding of the structural and intrinsic properties of materials that govern light-matter interactions. This research paves the way for the further development of thin film-based polarization filters and advanced optoelectronic device technologies.
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