GaN-based LEDs surrounded with a two-dimensional nanohole photonic crystal structure for effective laterally guided mode coupling

Abstract

Traditional implementation of photonic crystals (PhCs) on LED light emission surfaces results in weak coupling of light with the PhCs. Here we introduce a GaN-based LED surrounded with a nanohole PhC structure along the mesa edges. The laterally guided modes in the epi-structure can be effectively coupled with the two-dimensional periodic structure. The proposed structure results in the improvement of LED light extraction and provides flexibility of radiation directionality control.

High performance GaN-based LEDs on patterned sapphire substrate with patterned composite SiO_2/Al_2O_3 passivation layers and TiO_2/Al_2O_3 DBR backside reflector

“…This small θ c hinders the light extraction seriously, as most of the light beams with an incident angle larger than θ c will be reflected back to the LED and eventually absorbed by the GaN-based epitaxial layers. Therefore, several recent studies have focused on improving the LEE by changing light beam trajectories using various kinds of approaches, such as integration of two-dimensional photonic crystal structures [4][5][6], preparation of patterned sapphire substrate (PSS) [7][8][9][10][11][12], The air-gap DBR structure in LEDs, which acts as a light reflector to redirect light into the escape cones on both front and back sides of the LEDs, has also been developed [30-34]. By using DBR reflectors made of AlN, GaN, and AlGaN, highefficiency LEDs with emission wavelength varied from UV to visible range have been realized [35][36][37][38].…”

Study of GaN/InGaN Light-Emitting Diodes with Specific Zirconium Oxide (ZrO2) Layers

“…[1][2][3][4][5][6][7][8][9] However, based on the remarkable difference in refractive index between the surrounding air (n = 1) and GaN (n = 2.5), the critical angle of total internal reflection (TIR) is only of 23.5°, which seriously suppresses the total light output attributed to the lower light extraction efficiency (LEE) and the lower external quantum efficiency (EQE) of GaN/InGaN LEDs. [10][11][12][13] Recently, various methods, e.g., pattern sapphire substrate, 14 backside reflector, 15 antireflection layer, 16 textured surfaces and sidewalls, 17,18 microhole array, 19 photonic crystal structure, 20 and hybrid surface structure 21 have been reported to upgrade the performance of GaN/InGaN LEDs. Moreover, the current spreading (CS) is an important issue for GaN/InGaN LEDs.…”

Integrated p–n junction InGaN/GaN multiple-quantum-well devices with diverse functionalities

“…Figures 1(c) and 1(d) illustrate the light emission images for both LEDs obtained from the back side at a forward voltage of 5 V. The predominant emission is located at the region underneath the p-electrode. The light guided in-plane is diffracted outside at the mesa facets 19) or escapes into the air at the bottom rough surface caused by reactive ion etching.…”