Diode is also known as Crystal diode, abbreviation diode (diode), in addition, there are early vacuum electronic diodes; it is an electronic device with unidirectional conduction currents. In the semiconductor diode there is a PN junction two lead terminals, the electronic device in accordance with the direction of the voltage, with unidirectional current conduction. Generally speaking, crystal Diode is a P-n junction interface with the form of semiconductor sintering and nitrogen type semiconductor. The space charge layer is formed on both sides of the interface, and the electric field is constructed. When the external voltage equals zero, because the concentration difference of the carriers on both sides of the P-n junction causes the diffusion current and the drift current caused by the self-built electric field is equal to the electric equilibrium state, which is also the characteristic of the diode.