How Diodes Work

The main principle of the diode is to use the unidirectional conductivity of the PN junction, adding leads and packaging to the PN junction to become a diode.

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, and a self-built electric field is built. When there is no applied voltage, the diffusion current caused by the difference in carrier concentration on both 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 forward voltage bias in the outside world, the mutual suppression of the external electric field and the self-built electric field increases the diffusion current of the carriers and causes the forward current. When there is a reverse voltage bias outside, the external electric field and the self-built electric field are further strengthened, forming a reverse saturation current that is independent of the reverse bias voltage value within a certain reverse voltage range.

When the applied reverse voltage is high to a certain level, the electric field strength in the space charge layer of the PN junction reaches a critical value, resulting in a multiplication process of carriers, a large number of electron-hole pairs, and a large reverse breakdown current. , known as the breakdown phenomenon of the diode. The reverse breakdown of PN junction can be divided into Zener breakdown and avalanche breakdown.