Improving the Vertical Light-Extraction Efficiency of GaN-Based Thin-Film Flip-Chip LEDs With p-Side Deep-Hole Photonic Crystals

This study systematically investigates the light-extraction efficiency (LEE) of GaN-based thin-film flip-chip light-emitting diodes (TFFC LEDs) with deeply etched photonic crystals (PhC). The optimal structure can be obtained by scanning the structural parameters using a three-dimensional finite-difference time-domain simulation. The concentration of the internal emission pattern within a limited extraction cone is significantly influenced by several structural parameters. The light-collection enhancement within an extraction cone explains the peak LEE caused by optimized structural parameters such as the p-GaN thickness, the air-hole depth, the lattice constant and the filling factor. The maximum extraction efficiency can reach 65% in the case of a p-GaN thickness of 140 nm, air-hole depth of 240 nm, lattice constant of 350 nm and filling factor of 0.40. Additionally, fabricating the optimal electrical contacts on the planar top surface of the n side can contribute to a higher potential enhancement.