GaN material is etched by hot KOH aqueous solution,which improves the light extraction efficiency of GaN based vertical-electrodes light emitting diodes.The size and density of hexagonal cones on the N-face of GaN are the major factors which affect the vertical-electrodes LEDs' extraction efficiency.Through analyzing the relation between size and density of hexagonal cone and extraction efficiency under different etching condition,we get the etching condition to maximize the LEDs' extraction efficiency.Usin...