Characterization of Ultra-wide Bandgap Semiconductors

Ultra-wide bandgap (UWBG) semiconductors have emerged as critical materials for advancing microelectronics and potentially transforming electrical grids into more resilient, efficient systems. With significantly higher bandgaps than traditional materials such as Si and GaAs, UWBG semiconductors offer significant advantages such as improved power conversion efficiency, high-temperature operation, and reduced device size and weight. Despite their valuable properties such as high critical electric field and high breakdown voltage, these materials present unique challenges for their development. The research of this dissertation focuses on structural and chemical characterization of UWBG heterostructures using electron microscopy methods, addressing problems associated with mitigating structural defects and improvement of device performance and functionality. The materials studied include cubic boron nitride (c-BN)/diamond and aluminum boron nitride (AlBN)/sapphire heterostructures, as well as nanoCarbon contact layers on diamond thin films. For c-BN/diamond heterostructures, the effects of gas precursor concentration, growth temperature, and substrate cleaning on BN phase determination, defect density, and the orientation relationship between c-BN domains and the diamond substrate were investigated. By optimizing these parameters, an almost pure cubic phase with reduced defect density was achieved, though 111-type stacking faults and twinning defects remain problematic.For AlBN/sapphire heterostructures, the impact of growth temperature on crystal quality, and boron incorporation and uniformity in thin films was studied. Films grown at lower temperatures had high defect densities, which decreased with higher growth temperatures but with lower B concentration. Annealing mitigated these defects but caused increased B segregation and phase separation. The structural and chemical properties of nanoCarbon contact layers were studied based on different substrate orientation and applied voltage bias. Higher degree of initial ordered growth was observed on (100) vs. (111) diamond surfaces which led to a higher density of platelets. Changes in applied bias during growth resulted in nominal changes in film morphologies. Overall, this research has contributed to a better understanding of UWBG semiconductor technology by providing improved insights into the connection between growth methods and material properties, including defect mitigation methods, thereby helping to facilitate the development of more efficient and reliable electronic devices.