Working principle of diode

A crystal diode is a pn junction formed by p-type and n-type semiconductors, with space charge layers on both sides of its interface and a self built electric field. When there is no external voltage, the diffusion current caused by the difference in carrier concentration on both sides of the pn junction and the drift current caused by the self built electric field are equal and in an electric equilibrium state.

When there is a forward voltage bias from the outside, the mutual suppression effect of the external electric field and the self built electric field increases the diffusion current of carriers, causing a forward current. When there is a reverse voltage bias from the outside, the external electric field and the self built electric field are further strengthened, forming a reverse saturation current I0 that is independent of the reverse bias voltage value within a certain range of reverse voltage. When the applied reverse voltage reaches a certain level, the electric field strength in the space charge layer of the pn junction reaches a critical value, causing a doubling process of charge carriers and generating a large number of electron hole pairs, resulting in a significant reverse breakdown current, known as the breakdown phenomenon of diodes. The reverse breakdown of pn junction can be divided into Zener breakdown and Avalanche breakdown.