Diodes & Rectification — A/L Physics

Semiconductor Diode A two-terminal device that allows current to flow primarily in one direction. A PN junction diode is formed by joining P-type (holes as majority carriers) and N-type (electrons as majority carriers) semiconductor materials. When forward-biased (P positive, N negative), the depletion region narrows and current flows. When reverse-biased, the depletion region widens, blocking current (except for a tiny leakage current). Real-world example: The LED indicator on a power supply — it lights only when current flows in the correct direction.

Forward Bias & Reverse Bias Forward bias: external voltage applied to reduce the potential barrier across the junction. Reverse bias: external voltage applied to increase the barrier. In forward bias, the diode conducts significantly above ~0.7 V for silicon (0.3 V for germanium). In reverse bias, only a negligible reverse saturation current flows until breakdown. Intuition: Think of a one-way valve in a water pipe — forward bias is water pushing the valve open; reverse bias pushes it shut.