A diode is a fundamental semiconductor device that allows current to flow in one direction while blocking it in the opposite direction. The working principle of a diode relies on its two semiconductor regions: the p-type and n-type regions.

When a forward voltage is applied to a diode, the p-n junction allows current to flow through, as the majority carriers move from the p-type to the n-type region. This forward biasing condition allows the diode to conduct, acting as a closed switch. On the other hand, applying a reverse voltage to the diode increases the p-n junction's depletion region, preventing current flow and behaving as an open switch.

Diodes have several applications in electronic circuits. They are commonly used as rectifiers, converting AC voltage into DC voltage, by permitting current flow during positive half cycles and blocking it during negative half cycles. Diodes also work as voltage regulators, limiting voltage spikes or surges, and protecting electronic components. Additionally, diodes are key elements in signal demodulation, signal multiplication, and various analog and digital electronic designs.