How Diodes Work

The crystal diode is a PN junction formed by a p-type semiconductor and an n-type semiconductor, a space charge layer is formed on both sides of the interface of the PN junction, and a self-built electric field is built. When there is no applied voltage, the diffusion current caused by the carrier concentration difference between the two sides of the PN junction is equal to the drift current caused by the self-built electric field and is in an electrical equilibrium state.

When there is a positive voltage bias in the environment, the mutual suppression effect of the external electric field and the self-built electric field increases the diffusion current of carriers and causes the forward current. When there is a reverse voltage bias in the outside, the external electric field and the self-built electric field are further strengthened to form a reverse saturation current I0 which is independent of the reverse bias voltage value within a certain reverse voltage range. When the applied reverse voltage is high to a certain extent, the electric field intensity in the space charge layer of the PN junction reaches a critical value to generate the multiplication process of carriers, generate a large number of electron-hole pairs, and generate a large reverse breakdown current, which is called the breakdown phenomenon of the diode. The reverse breakdown of PN junction can be divided into zener breakdown and avalanche breakdown.