Growth, processing and chracterization of gallium nitride based coaxial LEDs grown by MOVPE
Gallium nitride (GaN) based coaxial (core-shell type) light emitting diodes (LEDs) offer a wide range of advantages. The active region of these LEDs is located on non-polar, {1-100} m-plane GaN sidewalls, which helps eliminate the quantum confined Stark effect (QCSE) and improve the radiative recombination efficiency of LEDs. The recent evolution of a catalyst free, scalable, repeatable and industrially viable device quality GaN nanowire and nanowall metal organic vapor phase epitaxy (MOVPE) growth process has enhanced the possibility of these LEDs going into production from laboratory. Previous work has shown that these nanowires exhibited an intense photoluminescence (PL), in spite of their large surface-area to volume ratio, and lasing was observed when these nanowires were optically pumped at high intensity. In this dissertation, it is shown that as long as the GaN three dimensional (3D) structures have their critical dimension below a micron, the threading defect (TD) density along the c- direction approaches zero. A TD that enters into this structure bends towards the surface vii ({1-100} m-plane side wall) in its vicinity, thereby reducing its dislocation line energy. The possibility of growing zero defect GaN templates is extremely important in the breakdown voltage improvement, the reverse bias leakage current reduction and efficiency droop reduction. This growth method has also been extended to device quality micron sized features, thereby presenting us with opportunity to study and explore LEDs of different sizes and shapes. In addition to the microstructure growth, two different repeatable approaches have been identified and demonstrated for the microelectronic processing of these micron-sized LEDs. Despite being far from perfect, the characterization results obtained from these LEDs have been encouraging. The technological challenges associated with the fabrication of the coaxial LEDs are also discussed in this dissertation.
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