Light emitting diode

A light emitting diode, comprising:

• a substrate;
• an n-type semiconductor layer and a p-type semiconductor layer, located on the substrate;
• and
• an active layer, located between the n-type semiconductor layer and the p-type semiconductor layer, wherein the active layer comprises i quantum wells and (i+1) quantum barrier layers, each of the quantum wells is located between any two of the quantum barrier layers, where i is a natural number greater than or equal to 1, each of k quantum wells among the i quantum wells is constituted of a light emitting layer and an auxiliary layer, wherein a lattice constant of the quantum barrier layer is a1, a lattice constant of the light emitting layer is a2 and a lattice constant of the auxiliary layer is a3, a1<a2<a3, where k is a natural number greater than or equal to 1 and k≦i.

A light emitting diode, comprising:

• a gallium nitride (GaN) substrate comprising a first surface and a second surface respectively disposed on two sides of the GaN substrate, the second surface has a plurality of protuberances, a height of the protuberances is h μm, and a distribution density of the protuberances on the second surface is d cm−2, where h2d≧9.87×107, and h≦1.8;
• an n-type semiconductor layer, disposed on the first surface of the GaN substrate;
• an active layer, disposed on the n-type semiconductor layer, and a wavelength of light emitted by the active layer is between 340 nm and 450 nm;
• and
• a p-type semiconductor layer, disposed on the active layer.