The most important characteristic of semiconductor diodes is the single pass. That is, when DC voltage is applied, its resistance (forward resistance) is relatively small, and the current passing through is relatively large; When a reverse voltage is applied, it presents a large resistance (reverse resistance) and a small current.

A semiconductor diode is a two-ended electronic device that utilizes semiconductor properties. The most common semiconductor diodes are PN junction diodes and metal semiconductor contact diodes. Their common feature is that the voltammetry characteristics are asymmetrical, that is, the current shows good conductivity in one direction and high resistance in the opposite direction. It can be used for rectification, detection, voltage regulation, constant current, varactor diode, switch, light and photoelectric conversion, etc. By using the tunneling effect of carriers in the highly doped PN junction, the tunnel diode of ultra-high frequency amplification or ultra-high speed switching can be made.