Double-Grating Displacement Structure for Improving the Light Extraction Efficiency of LEDs

Abstract

To improve the light extraction efficiency of light-emitting diodes (LEDs), grating patterns were etched on GaN and silver film surfaces. The grating-patterned surface etching enabled the establishment of an LED model with a double-grating displacement structure that is based on the surface plasmon resonance principle. A numerical simulation was conducted using the finite difference time domain method. The influence of different grating periods for GaN surface and silver film thickness on light extraction efficiency was analyzed. The light extraction efficiency of LEDs was highest when the grating period satisfied grating coupling conditions. The wavelength of the highest value was also close to the light wavelength of the medium. The plasmon resonance frequencies on both sides of the silver film were affected by silver film thickness. With increasing film thickness, plasmon resonance frequency tended toward the same value and light extraction efficiency reached its maximum. When the grating period for the GaN surface was 365 nm and the silver film thickness was 390 nm, light extraction efficiency reached a maximum of 55%.

Study of GaN LED ITO Nano-Gratings With Standing Wave Analysis

“…Since GaN has a high index of refraction compared to air, light can only escape from the LED if it approaches the surface within 23 of normal. Adding a material with an index of refraction between the indices of GaN and air to the LED surface increases the limiting angle [3]- [7]. Creating sub-wavelength nanostructures at the LED surface can also increase the limiting angle by having a graded index of refraction between GaN and air that has anti-reflection properties [8].…”

“…However, most publications on transmission gratings are either focused on micro-grating simulation [3] or are experiments in the micro-grating [4]- [9], [4]- [14] or nano-grating [18]- [20], [23], [24] ranges. In their research, the types of gratings vary: some researchers use uniform geometrical patterns [6], [7], [19]- [24], while others use randomly placed geometrical surface features [14], [19], [22]. In a third and simpler approach, researchers roughen the LED surface to increase the number of angles that light can strike the surface [16]- [18].…”

Light Extraction From Scintillating Crystals Enhanced by Photonic Crystal Structures Patterned by Focused Ion Beam

“…Scintillating crystals and other high refractive index materials (e.g. LED) patterned with PhC (Photonic Crystals) shows better light output [2][3][4][5] compared to unpatterned samples. Snell's law states that light can only pass from the medium with higher refractive index to a medium with lower refractive index, when the angle of interaction is smaller than critical angle θC.…”

“…This can be partly overcome by nano-structuring of the interface between materials. By using PhC -gratings it is possible to extract part of the light which normally would be internally reflected [4] [5], this increase the light output from the crystal which can improve the quality of medical imaging. Future accelerators and particle physics experiments can benefit from this technology, which help them to cope with high luminosity and timing constraints.…”

The Influence of Sub-Wavelength Effective Refractive Index Layer on the Transmittance of LYSO Scintillator

“…The light is scattered at the interfaces where the refraction index changes, the scattered light waves are able to interfere with each other (destructively or constructively). One may find number of theoretical and experimental papers devoted to photonic crystals patterns on the surface of LYSO crystals to increase the efficiency of scintillator detectors [10][11][12][13].…”