What is the purpose of the depletion region in a diode?

The purpose of the depletion region in a diode is to allow or prohibit current flow depending on the applied voltage bias. In a diode, the depletion region forms at the junction of p-type and n-type semiconductor materials, where electrons from the n-type material recombine with holes from the p-type material. This region is essentially void of free charge carriers, which creates an electric field that plays a crucial role in the diode's operation.

When a forward bias is applied (where the p-side is connected to a higher voltage than the n-side), the electric field is reduced, allowing charge carriers to recombine and current to flow. Conversely, when a reverse bias is applied, the electric field widens the depletion region, preventing charge carriers from crossing the junction and effectively blocking current flow. This behavior is fundamental to the diode's functionality, enabling it to act as a rectifier by permitting current to flow in one direction while restricting it in the opposite direction.