A diode that has been specially designed to break down at a particular voltage, consisting of a p-n junction with high doping concentrations on either side of the junction. It acts as a rectifier until the applied reverse voltage reaches a certain value, known as the Zener breakdown voltage, when the device becomes conducting. This effect occurs as a result of electrons being excited directly from the valence band into the conduction band. Used as a clamp for voltage regulation. Named after C. M. Zener.