<P> The emitter - base Zener diodes can handle only smaller currents as the energy is dissipated in the base depletion region which is very small . Higher amount of dissipated energy (higher current for longer time, or a short very high current spike) causes thermal damage to the junction and / or its contacts . Partial damage of the junction can shift its Zener voltage . Total destruction of the Zener junction by overheating it and causing migration of metallization across the junction ("spiking") can be used intentionally as a' Zener zap' antifuse . </P> <P> A subsurface Zener diode, also called' buried Zener', is a device similar to the Surface Zener, but with the avalanche region located deeper in the structure, typically several micrometers below the oxide . The hot carriers then lose energy by collisions with the semiconductor lattice before reaching the oxide layer and cannot be trapped there . The Zener walkout phenomenon therefore does not occur here, and the buried Zeners have voltage constant over their entire lifetime . Most buried Zeners have breakdown voltage of 5--7 volts . Several different junction structures are used . </P> <P> Zener diodes are widely used as voltage references and as shunt regulators to regulate the voltage across small circuits . When connected in parallel with a variable voltage source so that it is reverse biased, a Zener diode conducts when the voltage reaches the diode's reverse breakdown voltage . From that point on, the relatively low impedance of the diode keeps the voltage across the diode at that value . </P> <P> In this circuit, a typical voltage reference or regulator, an input voltage, U, is regulated down to a stable output voltage U . The breakdown voltage of diode D is stable over a wide current range and holds U relatively constant even though the input voltage may fluctuate over a fairly wide range . Because of the low impedance of the diode when operated like this, resistor R is used to limit current through the circuit . </P>

How to find breakdown voltage of zener diode