Dioda

Meet Dioda, a one-way gate for electric current.

A diode is a junction between p-type and n-type semiconductor. At the junction a thin depletion region forms, with almost no free charge carriers and a built-in voltage across it. A forward voltage shrinks that barrier, and current rises exponentially. A reverse voltage widens it, and only a tiny leakage current, the saturation current I_s, flows. The Shockley diode equation describes this, named after William Shockley, co-inventor of the transistor.

The key scale is the thermal voltage V_T = kT/q. At 300 K, V_T = 1.380649 × 10⁻²³ × 300 / 1.602 × 10⁻¹⁹ ≈ 0.0259 V, about 26 mV. With n = 1, every extra 0.06 V forward multiplies the current by about ten.

Diodes rectify alternating current into direct current in chargers and power supplies, and protect circuits from reversed batteries. Light-emitting diodes are diodes that give out light when current flows.

The equation ignores the diode's internal resistance at high current, and it fails in reverse breakdown, when a large reverse voltage suddenly lets current flow. It also changes with temperature.