The positive z direction relative light extraction efficiency of GaN light-emitting diodes with microstructure slab is calculated by three-dlmensional finite-difference time-domain method, where the microstructure slab consists of a graphite lattice of pillars. The results show that the two-dimensional graphite-arranged pillars suppress light extraction. When there is a thick pillar in the middle of the pillars, the structure can enhance light extraction of the light-emlttlng diodes. The tower-like pillars, which are thin on the top of the pillars and thick on the bottom of the pillars, benefit the light extraction when the angle of the tower-like pillars is proper.
