forwardbias

Forward bias is a condition applied to a p-n junction or diode in which the external voltage reduces the built-in potential barrier across the junction, allowing significant current to flow. It is the opposite of reverse bias, where the applied voltage widens the depletion region and suppresses current.

Physically, forward bias narrows the depletion region, increases carrier injection across the junction, and raises the rate of recombination in the active region. The resulting current is strongly dependent on the applied voltage and can be described by the Shockley diode equation I = I_S (exp(V/(nV_T)) - 1), where V is the voltage across the junction, I_S the saturation current, V_T ≈ kT/q (~25 mV at room temperature), and n the ideality factor (typically between 1 and 2).

Common devices exhibit characteristic forward-voltage drops: silicon diodes typically begin conducting noticeably around 0.6–0.7 V at moderate currents; germanium diodes around 0.2–0.3 V; Schottky diodes at even lower values. Light-emitting diodes usually require higher forward voltages, often in the 2–3 V range depending on color and construction.

Forward bias is used in rectifiers, signal diodes, and optoelectronic devices. In LEDs, forward bias not only conducts current but also creates radiative recombination that emits light, while in power applications it determines power dissipation and efficiency.