Improved Light Extraction of LEDs with Nanomesh ZnO Layers and Photonic Crystals

• Main Authors: An-Fei Lee, 李安飛
• Other Authors: Yan-Kuin Su
• Format: Others
• Language: en_US
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/55902403062593880204

碩士 === 國立成功大學 === 微電子工程研究所碩博士班 === 97 === Light-emitting diodes ( LEDs ) are becoming an increasingly attractive alternative to conventional light sources due to their promising potential. Rapid progress in research and development is dedicated to improving LEDs performance through the use of more efficient structures. However, the external quantum efficiency of LEDs has a significant gap due to low light extraction, although internal quantum efficiency has been reach 90% above. Here, we demonstrate an improving in the light extraction of AlGaInP and GaN LEDs using nanomesh ZnO layers and photonic crystals, respectively. Instead of using conventional electron-beam lithography, the nanosphere lithography was utilized to fabricate these nano-scale structures of LEDs due to its high throughput and effective-cost. In part of AlGaInP LEDs with nanomesh ZnO layer, the light output power revealed an increase by 14% at 20 mA injection current. In additional, the graded refractive index structure of ZnO/SiO2 layers also enhanced light output about 24% as compared to conventional AlGaInP LEDs. The improving light extraction were attributed to more light scattering by nanomesh ZnO layer and reduce the total internal reflection at semi-air interface by graded index structure effectively . In part of PC GaN LEDs, the PC patterns with two-dimensional hexagonal-lattice GaN-pillar array were integrated on the p-GaN layer by nanosphere lithography and ICP dry etching. Two types PC structures under the same lattice constant of 220 nm by simulation results of two-dimensional plane-wave expansion were fabricated to study the effect of photonic bandgap ( PBG ) to light extraction. One is PC 150 nm designed to posses a PBG within the blue emission light, the other is PC 180 nm without PBG. The light output power of the PC 150 nm with PBG was significantly enhanced by 13% in comparison to the PC 180 nm without PBG. It indicated that the PC structure with PBG can get further enhancement of light extraction in GaN LEDs due to the PBG effect.