A light-emitting diode, comprises an active layer for emitting a light with a phase and a peak wavelength λ in air, a reflector, a lower semiconductor stack between the active layer and the reflector, wherein the lower semiconductor stack comprises multiple semiconductor layers, and each of the multiple semiconductor layers has a refractive index ni, a thickness di and two sides each contacting adjacent layers to form two interfaces, wherein each interface has a phase shift when the light passes through the interface.