• GaN LEDs;
  • laser lift-off;
  • light extraction;
  • wet etching


By lifting-off the patterned sapphire substrate of flip-chip GaN-based light emitting diodes, a 2-D periodic pattern of inverted circular cavities was created on the N-polar GaN (N-GaN) surface. The inverted circular cavities on the N-GaN surface evolve to discrete volcanic craters by wet etching in hot KOH solution. The formation of volcanic craters greatly enhances the light extraction efficiency on the patterned GaN surface by 27%. In addition, a correlation is observed between the threading dislocation distribution and the etching pattern on the N-GaN surface, which implies that the threading dislocation seemingly guides the etching on the N-GaN surface. A dislocation-orientated etching mechanism on the N-GaN surface is proposed in this study.