Fabrication of GaN-Based Light Emitting Diodes with Decorated Micro-sphere Surface Structures

• Main Authors: Yi-ChunChan, 詹逸群
• Other Authors: Wen-Chau Liu
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/8ek74u

碩士 === 國立成功大學 === 奈米積體電路工程碩士學位學程 === 104 === In this dissertation, for purposes of enhancing the light extraction efficiency (LEE), a series of GaN-Based light-emitting diodes (LEDs) with decorated micro-sphere surface structures are fabricated and studied. Novel materials and device fabrication processes, including fabrication of GaN-Based LEDs with hybrid SiO2 micro-spheres anti-reflection passivation layer by rapid convection deposition, GaN-Based LEDs with specific anti-reflection layer prepared by SiO2 micro-spheres filled in AZO current spreading layer, and GaN-Based LEDs with GaN-etched microhole arrays, are proposed to improve wall-plug efficiency (WPE). Thus, the enhanced performance of GaN-Based LEDs could be obtained. Optical and electrical properties of GaN-Based LEDs are studied and discussed. In addition, fabrication of various SiO2 anti-reflection structures are addressed and discussed in detail. First, GaN-Based LEDs with hybrid SiO2 micro-spheres anti-reflection passivation layer fabricated by rapid convection deposition (RCD) is studied. Without any degradation of electrical properties, the use of SiO2 anti-reflection passivation layer could improve surface roughness and light scattering. The enhanced light extraction of GaN-Based LEDs could be attributed to graded-refractive-index structure. Thus, the total internal reflection (TIR) could be reduced. As compared with a conventional GaN-Based LED at 20 mA, the studied device exhibits a 18.7% and 28.4% enhancement in light output power and luminous flux. Second, it is found that aluminum-doped zinc oxide (AZO) has similar electrical conducting and optical transparent properties with indium titanium oxide (ITO). In addition, due to the higher cost of ITO material, AZO was used for being transparent conducting layer (TCL) instead of ITO in this study. The SiO2 micro-spheres were filled in AZO microhole arrays which is formed by rapid convection deposition. Then, SiO2 thin film was deposited on the surface by DC sputter. Due to the presence of SiO2 anti-reflection layer, photons emitted from the active region could be scattered and redirected in arbitrary directions for light extraction. Thus, Fresnel reflection could be reduced. As compared with a conventional GaN-Based LED at 20 mA, the studied device exhibits a 17.1% and 23.8% enhancement in light output power and luminous flux. Finally, effects of the use of microhole array structure on GaN-Based LEDs are systematically studied and demonstrated in this work. The microhole array structure could expose large active layer on sidewall area, resulting in reduced reflection of light in the microhole array structure. In addition, the use of SiO2 nano-particles deposited on the etched sidewall surface, which could increase opportunity for the light escaping from the inside of LEDs. As compared with a conventional LED at 20 mA, the studied device exhibits 64.8% and 75.0% improvements in light output power and external quantum efficiency. All of these specific approaches, which are fabricated and studied in this dissertation, could improve performance of GaN-Based LEDs. To compete with traditional light sources in applications of solid-state lighting, high-performance GaN-Based LEDs could be expected to have some success.