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Laser-assisted Metal Organic Chemical Vapor Deposition of Gallium Nitride
Due to its unique properties, gallium nitride is of great interest in industry applications including optoelectronics (LEDs, diode laser, detector), high power electronics, and RF and wirelss communication devices. The inherent shortcomings of current conventional deposition methods and the ever-increasing demand for gallium nitride urge extended efforts for further enhancement of gallium nitride deposition. The processes of conventional methods for gallium nitride deposition, which rely on thermal heating, are inefficient energy coupling routes to drive gas reactions. A high deposition temperature (1000–1100 °C) is generally required to overcome the energy barriers to precursor adsorption and surface adatom migration. However, there are certain limitations associated with deposition methods that require high temperatures. As an intensive, coherent and monochromatic light, laser is an ideal candidate for exploring alternative energy coupling pathways. The laser techniques, in some instances, may offer processing advantages that are not available with conventional deposition methods. To address the challenges, the research efforts in this dissertation mainly focused on laser incorporation in metal organic chemical vapor deposition of gallium nitride films, which led to: 1) rapid growth of m-plane gallium nitride nanoplates 2) low-temperature growth of gallium nitride films 3) promotion of energy coupling efficiency; 4) enhancement of gallium nitride deposition; 5) fast growth of gallium nitride epilayers; and 6) realization of high-performance ultraviolet photodetectors based on the as-grown gallium nitride epilayers. The m-plane-oriented gallium nitride nanoplates were successfully grown on silicon substrates at 450 °C, using CO2 laser-assisted metal organic chemical vapor deposition with perpendicular geometries. Vibrational excitations of precursor molecules were realized using a kilowatt wavelength-tunable CO2 laser with a spectrum range from 9.2 to 10.9 µm. The resonant excitation of the NH-wagging mode of ammonia molecules was demonstrated to be more efficient than nonresonant excitations in promoting the deposition rate and improving the gallium nitride quality attributed to a higher energy coupling efficiency. Low-temperature growth of crystalline gallium nitride films on c-plane sapphire substrates was achieved by laser-assisted metalorganic chemical vapor deposition and coupling laser energy into the chemical reactions. A CO2 laser-assisted metal organic chemical vapor deposition approach was also successfully developed for the fast growth of high-quality gallium nitride epilayer on the sapphire (0001) substrate. By optimizing the growth parameters, the ~ 4.3 µm thick gallium nitride films showed excellent thickness uniformity and smooth surface with a root mean square.The ultraviolet photodetectors were also realized based on the as-grown laser-assisted metalorganic chemical vapor deposition gallium nitride layers, which exhibited a high responsivity and a fast response time.
Rabiee Golgir, Hossein, "Laser-assisted Metal Organic Chemical Vapor Deposition of Gallium Nitride" (2017). ETD collection for University of Nebraska - Lincoln. AAI10615178.