High refractive index difference between GaN-based light-emitting diode (LED) die material and surrounding medium causes low light extraction efficiency. Introduction of surface grooves to sapphire substrate side surfaces improves the light extraction efficiency of GaN-based LED die6 by altering the normal for the impinging light rays inside the substrate layer. Comparison of light output power given out by GaN-based LED die with grooved sapphire substrate and un-grooved sapphire substrate were studied using ray-tracing simulation. Three types of surface grooves at different aspect ratios were simulated which includes elliptical groove, triangular groove and rectangular groove. Based on the results obtained, GaN-based LED die with elliptically grooved sapphire substrate gives the best enhancement in light output power by 121.2426% compared to an un-grooved GaN-based LED die at an aspect ratio of 0.05. Surface grooves with curvature or angled plane gives a better enhancement in light extraction efficiency compared to a flat surface.
