Zener Voltage

Author: Leonard Krugman

If the reverse voltage applied across a P-N junction is gradually increased, a point is reached where the potential is high enough to break down covalent bonds and cause current flow. This voltage is called Zener voltage. In transistor application the Zener voltage has the same design importance as the inverse voltage rating of a vacuum tube, since it defines the maximum reverse voltage which can be applied to a junction without excessive current flow. The Zener potential for a transistor junction can be increased by widening the space charge layer, or by forming the junction so that the transition from N region to P region is a gradual process. In germanium, the Zener voltage field is around 2 x 10⁵ volts/centimeter. A transistor junction with a Zener potential of 70 volts would therefore have a space charge layer of 70/(210⁵)) = 3510^-5 centimeters.