Light Extraction Enhancement of GaN LEDs by Hybrid ZnO Micro-Cylinders and Nanorods Array

Abstract

A hybrid patterned ZnO micro-cylinders and nanorods array (MCNR) was fabricated to improve the light extraction efficiency for high brightness GaN-based light-emitting diodes (LEDs). The light extraction efficiency of the LEDs with the ZnO MCNR is increased by 86.4% compared with conventional planar LEDs. LEDs with ZnO MCNR have greater light extraction efficiency than those only with ZnO micro-cylinders or ZnO nanorods array. The optical-electrical characteristics and far-field radiation patterns are measured and analyzed. The local optical field distribution patterns of the LEDs with ZnO microcylinders, ZnO nanorods, and ZnO MCNR are investigated using confocal scanning electroluminescence microscopy. The higher light extraction enhancement effect of ZnO MCNR is attributed to that it combines the light outputting effect from side walls of ZnO micro-cylinders and the light scattering effect of ZnO nanorods array.Index Terms-GaN-based light-emitting diodes (LEDs), light extraction, zinc oxide (ZnO), patterned micro-cylinders, nanorods array.

Effect of ZnO nanostructures on the optical properties of white light-emitting diodes

“…ZnO nanostructures can be used as gradient refractive index layer because the refractive index of ZnO (n = 2.0) is between GaN (n = 2.5) and air (n = 1). Until now, researchers found that doping ZnO, especially with special nanostructures, into GaN-based blue LEDs was able to improve the light extraction [25][26][27][28][29]. Yin et al [26] applied a hybrid patterned ZnO micro-cylinders and nanorods array on the surface of LED chip to improve the light extraction efficiency for GaN-LEDs.…”

“…Until now, researchers found that doping ZnO, especially with special nanostructures, into GaN-based blue LEDs was able to improve the light extraction [25][26][27][28][29]. Yin et al [26] applied a hybrid patterned ZnO micro-cylinders and nanorods array on the surface of LED chip to improve the light extraction efficiency for GaN-LEDs. Yin et al [28] demonstrated a remarkable enhancement of light extraction efficiency in GaN based blue LEDs with rough beveled ZnO nanocone arrays grown on the planar ITO layer.…”

Fabrication of Polystyrene/ZnO Micronano Hierarchical Structure Applied for Light Extraction of Light-Emitting Devices

“…GaN-based LED chips were fabricated by sequentially growing undoped GaN (u-GaN, 2 μm), n-GaN (2 μm), five periods of InGaN/GaN multiple quantum wells (MQWs), p-GaN (250 nm), indium tin oxide (200 nm), and p- and n-type Cr/Au electrodes on c-plane sapphire substrates (400 μm), using a metal–organic chemical vapor deposition (MOCVD) process. The details of the LED-fabrication process can be found elsewhere. , The fabricated LED chips (set A) and silica glasses (set B) were used as substrates in equal experimental condition for further treatment.…”

Performance of GaN-Based LEDs with Nanopatterned Indium Tin Oxide Electrode

“…To increase the LEE of LEDs, several approaches had focused on fabricating micro-/nanostructures either inside or outside the LEDs [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. For example, roughed GaN surface [3][4][5][6][7], roughed sapphire substrate [8,9], roughed indium tin oxide (ITO) surface [10][11][12], and grown ZnO micro-/nanostructures [13][14][15] have been implemented in LEDs. The common nanoscale patterning techniques, such as electron-beam lithography [16], nanoimprint lithography [17], holographic lithography [18], hydrothermally method [19], and nanosphere lithography (NSL) [20], are used to obtain nanoscale surface textures.…”