Light-Emitting Diode (LED) is an optoelectronic device composed of p-type semiconductor and n-type semiconductor and emitting the light by means of the recombination of carriers at p-n interface. LED has the advantages of small volume, low power consumption, long working lifetime, and fast reaction speed. Therefore, light-emitting diodes are widely used in optical display devices, traffic lights, information storage apparatus, communication devices, illuminant devices and medical instruments.