Photonic bands in two-dimensionally patterned multimode GaN waveguides for light extraction

Abstract

International audienceWe observe experimentally by photoluminescence the band structure and specific emission properties of an in-plane, light-diffracting photonic crystal formed onto a multimode gallium nitride waveguide. Clear-cut two-dimensional photonic crystal effects are reported. Comparison with modeling results in identification of the band structure, provides insight into the light diffraction mechanism and points out design issues for enhancement of the extraction efficiency

Photonic-crystal GaN light-emitting diodes with tailored guided modes distribution

“…9 The filling factor is f = 0.3. As in previously measured PhCs samples, 16 we observe sets of bands stemming from the high-order modes. However, in contrast to previous results, a new, intense band now appears at lower frequency.…”

“…2͒. In contrast to previous measurements, 16 the direct emission from the LED could not be isolated and subtracted here, since the PhC diffracted in all directions. Therefore, the direct emission is present as a gray background ͑modulated by FabryPérot interferences of the GaN layer͒ on the spectra of Fig.…”

“…16 If we label modes by their effective index n eff , and n GaN is the index of GaN, low-order modes ͑say, n GaN Ͼ n eff Ͼ n GaN − 0.15͒ are mostly localized in the core of the GaN waveguide so that they barely overlap with the PhC, leading to poor diffraction efficiency. On the other hand, high-order modes ͑n GaN − 0.15Ͼ n eff Ͼ n sapphire ͒ have increased overlap with the PhC and acquire a better extraction rate.…”

“…16 Electroluminescence was collected at all angles ͑−90°to 90°͒ by a rotating arm and analyzed in a spectrometer. We collected both the direct emission of the LED, and the diffraction of the surrounding PhC.…”

Ga N ∕ In Ga N light emitting diodes with embedded photonic crystal obtained by lateral epitaxial overgrowth

“…[3][4][5][6][7][8] However, harnessing the full potential of PhCs has proved difficult: the largest light extraction enhancements reported in the literature are approximately twice, which are largely below theoretical expectations. Indeed, efficient PhCs require full optimization of the design, 9 including choices of the crystal lattice 6 and of the vertical structure.…”