Light-emitting diode

A light-emitting diode, comprising:

• an active layer for emitting a light ray with a phase and a peak wavelength λ in air;
• an upper semiconductor stack on the active layer;
• a reflector;
• and
• 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 ray travels through the two interfaces along a same direction, and
• wherein, for one of the multiple semiconductor layers traveled through by the light ray, the thickness di satisfies at least one of the following conditions of:
• (i) if the two phase shifts are the same, then 0.8*((2m−1)/2)*(λ/ni)≦di≦1.2*((2m−1)/2)*(λ/ni), where m is a natural number;
• and
• (ii) if the two phase shifts are different, then 0.8*((2m−1)/4)*(λ/ni)≦d≦1.2*((2m−1)/4)*(λ/ni), where m is a natural number.