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In this dissertation, various characterization techniques have been used to investigate many aspects of the properties of III-nitride materials and devices for optoelectronic applications.

The first part of this work is focused on the evolution of microstructures of BAlN thin films. The films were grown by flow-modulated epitaxy at 1010

In this dissertation, various characterization techniques have been used to investigate many aspects of the properties of III-nitride materials and devices for optoelectronic applications.

The first part of this work is focused on the evolution of microstructures of BAlN thin films. The films were grown by flow-modulated epitaxy at 1010 oC, with B/(B+Al) gas-flow ratios ranging from 0.06 to 0.18. The boron content obtained from X-ray diffraction (XRD) patterns ranges from x = 0.02 to 0.09, while Rutherford backscattering spectrometry (RBS) measures x = 0.06 to 0.16. Transmission electron microscopy indicates the sole presence of the wurtzite crystal structure in the BAlN films, and a tendency towards twin formation and finer microstructure for B/(B+Al) gas-flow ratios greater than 0.15. The RBS data suggest that the incorporation of B is highly efficient, while the XRD data indicate that the epitaxial growth may be limited by a solubility limit in the crystal phase at about 9%. Electron energy loss spectroscopy has been used to profile spatial variations in the composition of the films. It has also located point defects in the films with nanometer resolution. The defects are identified as B and Al interstitials and N vacancies by comparison of the observed energy thresholds with results of density functional theory calculations.

The second part of this work investigates dislocation clusters observed in thick InxGa1-xN films with 0.07 ≤ x ≤ 0.12. The clusters resemble baskets with a higher indium content at their interior. Threading dislocations at the basket boundaries are of the misfit edge type, and their separation is consistent with misfit strain relaxation due the difference in indium content between the baskets and the surrounding matrix. The base of the baskets exhibits no observable misfit dislocations connected to the threading dislocations, and often no net displacements like those due to stacking faults. It is argued that the origin of these threading dislocation arrays is associated with misfit dislocations at the basal plane that dissociate, forming stacking faults. When the stacking faults form simultaneously satisfying the crystal symmetry, the sum of their translation vectors does add up to zero, consistent with our experimental observations.
ContributorsWang, Shuo, Ph.D (Author) / Ponce, Fernando A. (Thesis advisor) / Menéndez, Jose (Committee member) / Rez, Peter (Committee member) / McCartney, Martha (Committee member) / Arizona State University (Publisher)
Created2018
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In this dissertation, far UV spectroscopy is applied to investigate the optical properties of dielectric thin films grown by atomic layer deposition. The far UV (120 – 200 nm) reflectance for several dielectric oxides and fluorides, including AlF3, Al2O3, Ga2O3, HfO2, and SiO2, was measured at variable angles and thicknesses.

In this dissertation, far UV spectroscopy is applied to investigate the optical properties of dielectric thin films grown by atomic layer deposition. The far UV (120 – 200 nm) reflectance for several dielectric oxides and fluorides, including AlF3, Al2O3, Ga2O3, HfO2, and SiO2, was measured at variable angles and thicknesses. Multiple optical calculation methods were developed for the accurate determination of the optical constants from the reflectance. The deduced optical constants were used for optical designs, such as high-reflectivity coatings, and Fabry-Perot bandpass interference filters. Three filters were designed for use at 157 nm, 212 nm, and 248 nm wavelengths, based on multilayer structures consisting of SiO2, Al2O3, HfO2, and AlF3. A thorough error analysis was made to quantify the non-idealities of the optical performance for the designed filters. Far UV spectroscopy was also applied to analyze material mixtures, such as AlF3/Al and h-BN/c-BN mixtures. Using far UV spectroscopy, different phases in the composite can be distinguished, and the volume concentration of each constituent can be determined. A middle UV reflective coating based on A2O3 and AlF3 was fabricated and characterized. The reflective coating has a smooth surface (?? < 1 nm), and a peak reflectance of 25 – 30 % at a wavelength of 196 nm. The peak reflectance deviated from the design, and an analysis of the AlF3 layer prepared by plasma-enhanced atomic layer deposition (PEALD) indicated the presence of Al-rich clusters, which were associated with the UV absorption. Complementary techniques, such as spectroscopic ellipsometry, and X-ray photoelectron spectroscopy, were used to verify the results from far UV spectroscopy. In conclusion, this Dissertation demonstrated the use of in-situ far UV spectroscopy to investigate the optical properties of thin films at short wavelengths. This work extends the application of far UV spectroscopy to ultrawide bandgap semiconductors and insulators. This work supports a path forward for far UV optical filters and devices. Various errors have been discussed with solutions proposed for future research of methods and materials for UV optics.
ContributorsHuang, Zhiyu (Author) / Nemanich, Robert (Thesis advisor) / Ponce, Fernando (Committee member) / Menéndez, Jose (Committee member) / Holman, Zachary (Committee member) / Arizona State University (Publisher)
Created2021