The diode is also known as the crystal diode, referred to as diode (diode), in addition, there are early vacuum electron diode; it is a kind of electronic device with a unidirectional conduction current. In the semiconductor diode inside a PN junction two lead terminals, this electronic device in accordance with the direction of the applied voltage, with a unidirectional current transduction. Generally, a crystal diode is a p-n junction interface formed by sintering a p-type semiconductor and an n-type semiconductor. A space charge layer is formed on both sides of its interface, constituting a self-built electric field. When the applied voltage is equal to zero, due to the difference in the concentration of carriers on both sides of the p-n junction caused by the diffusion current and the drift current caused by the self-built electric field is equal and in a state of electrical equilibrium, which is also the normal diode characteristics.