Ion implantation is carried out into a GaN layer of mLEDs to partially or fully convert one or more regions of the crystalline GaN layer to amorphous GaN. As a result, the GaN layer through which light rays propagate have non-uniform refractive indexes that modify propagation paths of some light rays. Ions can be implanted in a region around an active region that emits light to function as an optical waveguide. The ion implanted regions direct light rays that propagate along predetermined directions into predetermined propagation paths thereby to modify the angle of incidence of these light rays. As such, the light extraction efficiency of the mLEDs is increased.