Growth and applications of Group III-V nitrides

Autor: Kuo,Chien-Ting, 郭建廷
Rok vydání: 2017
Druh dokumentu: 學位論文 ; thesis
Popis: 105
A site-controlled crystalline InN growth from the V-pits of a GaN substrate was investigated. The V- pits were fabricated by epitaxial lateral growth of GaN over SiO2 disks patterned on a sapphire substrate. InN crystals were found to preferably grow on the inclined {10-11} crystal planes of the V-pits. A V-pit size of 1 μm or less can provide precise site-controlled InN nucleation at the V-pit bottom, while no InN was grown on the rest of the exposed GaN surfaces. The site-controlled nucleation is attributed to the low surface energy point created by the converging six {10-11} crystal facets at the V-pit bottom. When In source supply is below a certain value, this V-pit bottom is the only location able to aggregate enough active sources to start nucleation, thereby providing site-controlled crystal growth. We report two types of crown-shaped with air void in a typical AlGaN-based ultraviolet light-emitting diode (UV-LEDs) with embedded air void array grown by metal–organic chemical vapor deposition are fabricated and investigated. The simulation results demonstrate that the proposed 1.5μm crown-shaped patterned sapphire substrates (CPSS) UV-LEDs (λ~369nm) have better device performances. The concept of introducing air-void structures into AlGaN-based LEDs is well recognized for its ability to enhance the light extraction efficiency (LEE). The LEE analyzed using optical simulation tools based on Monte Carlo method and the ray-tracing simulation results are further validated experimentally by fabricating real devices. The Monte Carlo ray-tracing simulation reveals that the light extraction of the air-voids embedded LED was dramatically increased due to a strong light reflection and redirection by the air voids. The high performance GaN based light-emitting diodes (LEDs) with embedded air void array grown by metal–organic chemical vapor deposition (MOCVD). The transmission electron microscopy images demonstrate that the threading dislocations were significantly suppressed by epitaxial lateral overgrowth (ELOG). The Monte Carlo ray-tracing simulation reveals that the light extraction of the air-voids embedded LED was dramatically increased due to a strong light reflection and redirection by the air voids. The influence of the microstructure geometry of patterned sapphire substrates (PSS) on the light extraction efficiency (LEE) of GaN LED is numerically analyzed. Cone structures of various dimensions are studied, along with dome and mixed microstructures. LEE is found to mainly depend on the microstructure surface slope. LEE rises quickly with slope and flattens out when the slope exceeds 0.6. Scaling down the microstructure has little effect on LEE. Light rays are found to travel longer distances in PSS LEDs, as compared with LEDs grown on a flat substrate. Keeping GaN absorption loss low is important for LEE optimization.
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