| The rising energy cost has pushed for technological advances for high energy-efficiency technology. The United States spends more than ;In this dissertation, methods to achieve high efficiency III-Nitride LEDs emitting in the visible regime, by addressing the second and third challenges as mentioned above have been proposed and investigated. The novel approaches used to overcome the second and third challenges include: (1) reducing the dislocation density of GaN and increasing the internal quantum efficiency of LEDs through the use of a novel abbreviated GaN epitaxy growth mode on nano-patterned AGOG sapphire substrate, and (2) enhancing the light extraction efficiency of LEDs through the use of novel techniques such as SiO2/polystyrene microlens arrays, polydimethylsiloxane (PDMS) concave microstructure arrays, and TiO2 microspheres arrays.;The research works encompass various aspects: modeling and device design, epitaxial growth by metalorganic chemical vapor deposition, materials characterization and analysis, device fabrications, and device characterizations. The use of colloidal-based microlens arrays has led to significant enhancement of light extraction efficiency for both LEDs devices employing the concave and convex-based microlens arrays. The innovation in abbreviated growth mode on patterned substrate has led to the ability of realizing high quality GaN with reduced dislocation density and higher LED output power by employing a lower cost growth technique. |
