pnDiode

PN diode, short for pn junction diode, is a semiconductor device formed by joining p-type and n-type regions in a single crystal, creating a PN junction. The interface forms a depletion region with an internal electric field that acts as a barrier to the flow of charge carriers, enabling rectifying behavior.

Under no external bias, diffusion of carriers creates a built-in potential that prevents further current flow. Forward bias reduces the barrier and causes a rapid increase in current as majority carriers cross the junction, followed by minority-carrier diffusion. Reverse bias widens the depletion region, greatly reducing current to a small leakage level until breakdown occurs at a high reverse voltage.

The current–voltage relationship is highly nonlinear and is often described by the diode equation. In practical terms, a silicon PN diode conducts with a forward voltage drop of about 0.6 to 0.7 volts at moderate currents; germanium diodes have a lower drop, around 0.2 to 0.3 volts. In reverse bias, the current is usually small until breakdown.

PN diodes exhibit a variable junction capacitance that depends on bias, being higher under forward bias and lower under reverse bias due to changes in depletion width. They also show storage effects; when used for fast switching, reverse-recovery time becomes important, with slower diodes and faster Schottky variants used where speed matters.

Silicon is the most common material, with diodes formed by diffusion, ion implantation, or epitaxial growth. They are used for rectification, demodulation, and protection in power and signal circuitry, and exist in various forms for different applications, including high-speed and high-power designs.