Diode Working Principle (Forward Conductivity, Reverse Non-Conductivity)
A crystal diode is a p-n junction formed by p-type and n-type semiconductors. A space charge layer forms on both sides of the interface, and a built-in electric field is established. When no external voltage is applied, the diffusion current caused by the carrier concentration difference across the p-n junction and the drift current caused by the built-in electric field are equal, resulting in an electrical equilibrium state. When a forward bias is applied, the mutual cancellation effect between the external electric field and the built-in electric field increases the diffusion current of the carriers, causing forward current (the reason for conductivity). When a reverse bias is applied, the external electric field and the built-in electric field are further strengthened, forming a reverse saturation current I0 that is independent of the reverse bias voltage value within a certain reverse voltage range (this is why it is non-conductive).
When the applied reverse voltage is high enough, the electric field strength in the p-n junction space charge layer reaches a critical value, causing a carrier multiplication process, generating a large number of electron-hole pairs, and producing a very large reverse breakdown current, known as diode breakdown.
