#zener effect

Another phenomenon occurs when the intensity of the electric field (voltage divided by distance known as a field strength) becomes high enough to pull valence electrons out of their valence orbits. This is known as a Zener eflect or high-field emission. The breakdown voltage of the Zener effect (approximately 4 to 5 V) is called the Zener voltage. This effect is distinctly different from the avalanche effect, which depends on high-speed minority carriers dislodging valence electrons. When the breakdown voltage is between the Zener voltage and the avalanche voltage, both effects may occur.