GaP, GaAs and other compound semiconductor materials are used in the substrates of ordinary LED red-yellow chips and highlighted four-element red-yellow chips, which can generally be made into N-type substrates. Lithography is carried out by wet process, and then chip is cut with emery wheel blade. The blue-green chip of GaN material is a sapphire substrate. Since the sapphire substrate is insulated, it cannot be used as a pole of LED. Both P/N electrodes must be made on the epitaxial surface through dry etching process and some passivation process. Sapphires are hard to chip with an emery wheel blade because of their hardness. Its process is generally more complex than GaP and GaAs LED.