“…The light within the heterojunction would be trapped and propagated inside the GaN layer via total internal reflection. This is because the differences of the refractive indices of sapphire, NiO, and GaN, which are approximately equal to 1.79, 2.33, and 2.64, respectively at ∼370 nm [18], forms an optical waveguide to confine light within the GaN layer [14]. Moreover, the light inside the NiO layer, experienced distributed multiple optical scattering, has the possibility to form closed-loop paths for light within the region under external excitation.…”