Semiconductor diodes are also called crystal diodes. It is an electronic device that can conduct current in one direction.

According to the material, it can be divided into germanium, silicon or gallium arsenide; according to the structure, it can be divided into point contact, PN junction, pin, Schottky barrier, heterojunction; according to the principle, it can be divided into tunnel, varactor, avalanche, step recovery, etc. It is mainly used for detection, mixing, parametric amplification, switching, voltage stabilization, rectification, etc. After the development of optical communication, led, photoelectric, avalanche photoelectric, pin photoelectric, semiconductor laser and other diodes appear.