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

  • 詹 逸群

Student thesis: Master's Thesis

Abstract

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 ?ux 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 ?ux 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
Date of Award2016 Jul 25
Original languageEnglish
SupervisorWen-Chau Liu (Supervisor)

Cite this

'