Two-dimensional photonic quasicrystal on the surface of GaN-based light emitting diodes

Abstract

Two-dimensional (2D) photonic crystal (PhC) patterns in regular four-fold symmetry (2PhC) and dodecagonal symmetric photonic quasicrystal (12PQC) with 970 nm lattice pitch have been formed by electron beam lithography on the surface of GaN-based light emitting diodes (LEDs). The symmetry of a 2D quasicrystal in this work was based on a square-triangle tiling system. The enhancement of light extraction was obtained from both the 2PhC and 12PQC introduced GaN-based LEDs, and 12PQC is favourable compared to 2PhC. To explore the physical properties, we proposed a method for inspecting diffraction behaviours of the PhC arrays. The results supplied a clear representation of the diffraction behaviours of 2PhC and 12PQC that correspond to their lattice symmetry.

Lattice constant effects of photonic crystals on the extraction of guided mode of GaN based light emitting diodes

“…The trapped guided modes are partly out-coupled by 2PhCs, which leads to an improvement in the diffracted transmission of surface. In order to understand our results clearly, we made a simulation on a simplified model of a 2D shallow 2PhC grating whose depth of each PhC pattern was fixed at 150 nm on planar bulk GaN [13,15]. The calculation was obtained by rigorous coupled wave analysis (RCWA) which has been developed to accurately analyze the transmitted and reflected diffraction efficiency of a grating on the planar structures [16].…”

Light transmission from the large-area highly ordered epoxy conical pillar arrays and application to GaN-based light emitting diodes

“…To investigate the optical transmission properties of the nanostructured arrays, we have adopted a convenient approach of inspecting the cone or cylinder arrays on a special configuration of a transparent hemi-cylindrical epoxy sample similar to our previous reports. 13,29 The cone and cylinder arrays are transferred to the flat center of the specially designed transparent epoxy hemi-cylinder. In this way, we could then directly observe and measure the diffracted transmission depending on the incident light from the medium to air.…”

Enhancing light extraction of GaN-based blue light-emitting diodes by a tuned nanopillar array

“…[4] The majority of photons are reflected from the interface, become guided light in a waveguide formed by GaN and get reabsorbed. To increase the light extraction efficiency, various methods, such as roughed p-GaN surface, [5][6][7][8][9] roughed sapphire substrate, [10,11] photonic crystal [12][13][14][15][16] and patterned indium tin oxide (ITO) surface, [17][18][19] have been implemented in InGaN-based LEDs.…”