Analysis of light extraction efficiency enhancement for InGaN quantum wells light-emitting diodes with microspheres

The enhancement of light extraction efficiency for thin-film flip-chip (TFFC) InGaN quantum wells (QWs) light-emitting diodes (LEDs) with self-assembled microspheres on top of the n-GaN layer was studied. The light extraction efficiency of InGaN QWs LEDs for the three structures with 1) close-packed SiO₂ microlens; 2) close-packed SiO₂/polystyrene microlens; and 3) GaN micro-hemispheres were calculated and compared to that of the conventional InGaN QWs LEDs with flat surface. Three dimensional finite difference time domain (3D-FDTD) method was used to calculate the light extraction efficiency for TFFC InGaN/GaN QWs LEDs emitting at 460nm. The effects of the microsphere/micro-hemisphere diameter and the p-GaN layer thickness on the light extraction efficiency were studied. Studies show that the p-GaN layer thickness is critical for optimizing the TFFC LED light extraction efficiency. Light extraction efficiency enhancement of 1.7 times and 1.85 times were obtained in the TFFC LEDs with SiO₂ microlens and SiO₂/polystyrene microlens, respectively. More significant enhancement of the light extraction efficiency (>;2.6 times) was achieved from LEDs with GaN micro-hemispheres with optimized micro-hemisphere diameter of D=1μm and p-GaN thickness of 195nm.