Operation of Zener Diode

The Zener diode's operation depends upon the heavy doping of its p-n junction permitting electrons to tunnel from the valence band of the p-type material to the conduction band of the n-type material. Within the atomic scale, this tunneling corresponds to the transport of valence band electrons into the empty conduction band states; as a effect of the reduced barrier among these bands and high electric fields that are induced because of the comparatively high levels of dopings on both of the sides. The breakdown voltage could be controlled fairly accurately in the doping process. When tolerances within 0.05% (per cent) are available, the most extensively employed tolerances are 5% (per cent) and 10% (per cent). Breakdown voltage for generally available zener diodes can change widely from 1.2 volts to 200 volts.

Other mechanism which produces a similar effect is the avalanche effect like in the avalanche diode. The two sorts of diode are in fact constructed similar way and both effects are exist in diodes of this type. In silicon diodes up to approximately 5.6 volts, Zener effect is the predominant effect and depicts a marked negative temperature coefficient. Above 5.6 volts, the avalanche effect turns into predominant and shows a positive temperature coefficient. In a 5.6 V diode, the two effects take place together and their temperature coefficients neatly cancel each other out, so the 5.6 V diode is the component of choice in temperature-critical applications. Current manufacturing techniques have generated devices with voltages lower than 5.6 V with negligible temperature coefficients, but since higher voltage devices are encountered, the temperature coefficient increases radically. A 75 V diode has 10 times the coefficient of a 12 V diode. All such types of diodes, regardless of breakdown voltage, are generally marketed under the umbrella term of "Zener diode".