Light extraction simulation of surface-textured light-emitting diodes by finite-difference time-domain method and ray-tracing method

The light extraction efficiency (eta(1)) of surface-textured light-emitting diodes (LEDs) is calculated using a simulation based on the combination of the finite-difference time-domain (FDTD) method and the ray-tracing method. Considering the transmittance and light-scattering effects, which depend on the size of the surface-textured structure (STS), we investigated the dependence of ill on the size of the STS including the period and aspect ratio. As a result, a clear dependence on the size of the STS has been shown. Furthermore, by optimizing the size of the STS, we found eta(1) to be about 4 times larger than that of the surface flat structure (SFS). In addition, we demonstrated that the absorption coefficient of the GaN layer (alpha(GaN)) affected eta(1) of the STS more strongly than that of the SFS. We suggest that both wide light-scattering and a high GaN crystalline quality are important points for improving eta(1) when texturing the top surface of LEDs.