Elimination of total internal reflection in GaInN light-emitting diodes by graded-refractive-index micropillars

Abstract

A method for enhancing the light-extraction efficiency of GaInN light-emitting diodes (LEDs) by complete elimination of total internal reflection is reported. Analytical calculations show that GaInN LEDs with multilayer graded-refractive-index pillars, in which the thickness and refractive index of each layer are optimized, have no total internal reflection. This results in a remarkable improvement in light-extraction efficiency. GaInN LEDs with five-layer graded-refractive-index pillars, fabricated by cosputtering TiO2 and SiO2, show a light-output power enhanced by 73% and a strong side emission, consistent with analytical calculations and ray-tracing simulations.

Increased Light Extraction From GaN Light-Emitting Diodes by ${\rm SiN}_{{\rm x}}$ Compound Eyes

“…Hence, it was necessary to calculate the TIR and FR according to the geometry of the MLAs and the period of the SWS in order to determine the optimal height of the MLAs and the period of the SWS, respectively. In the case of the calculation of the TIR by ray tracing [21], the model used in this calculation was constructed for SiN x MLAs with diameters of 2 μm and separation lengths of 1 μm, whose valves were determined according to the height of MLAs. Fig.…”

The efficiency of UV LEDs based on GaN/AlGaN heterostructures

“…The main factor limiting the light extraction from the chip and reducing the efficiency of LEDs is total internal reflection [4,5] at the interface of materials with high and low optical density. The effective way to solve this issue is to introduce into the structure the surfaces that scatter light.…”

Shape designing for light extraction enhancement bulk-GaN light-emitting diodes

“…Photons generated from the quantum wells have been majorly trapped as a guided modes, with 66% trapped in the GaN, and 22% trapped in the sapphire substrates. 1 To alleviate these issues, many solutions have been developed, such as ZnO-Nanowire Array, 2 photonics crystal structures, 3 grade-refractive-index, [4][5][6] and surface plasmons. [7][8][9] Geometrical chip shaping [10][11][12][13] was another approach to increase the light extraction efficiency.…”