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Keywords:

  • GaN;
  • GRIN;
  • light-extraction;
  • micro-pillars

Abstract

A GaN waveguide structure with micro-pillar arrays is designed and fabricated to measure the extraction of optical modes that would be waveguided in the absence of the pillars. Electroluminescence (EL) measurements of waveguide light-emitting diodes (LEDs) with pillar diameters in the 2–10 µm range revealed increasing light-extraction efficiency (LEE) enhancement with decreasing pillar diameter. Ray tracing simulations of LED far-field patterns confirmed experimental trends. A 54% enhancement is demonstrated for GaN waveguides cladded with a triangular lattice of graded-refractive-index (GRIN) TiO2[BOND]SiO2 micro-pillars of 2 µm diameters compared to GaN waveguides cladded with an unpatterned GRIN TiO2[BOND]SiO2 layer.