<P> Because the p - type material is now connected to the negative terminal of the power supply, the' holes' in the p - type material are pulled away from the junction, leaving behind charged ions and causing the width of the depletion region to increase . Likewise, because the n - type region is connected to the positive terminal, the electrons will also be pulled away from the junction, with similar effect . This increases the voltage barrier causing a high resistance to the flow of charge carriers, thus allowing minimal electric current to cross the p--n junction . The increase in resistance of the p--n junction results in the junction behaving as an insulator . </P> <P> The strength of the depletion zone electric field increases as the reverse - bias voltage increases . Once the electric field intensity increases beyond a critical level, the p--n junction depletion zone breaks down and current begins to flow, usually by either the Zener or the avalanche breakdown processes . Both of these breakdown processes are non-destructive and are reversible, as long as the amount of current flowing does not reach levels that cause the semiconductor material to overheat and cause thermal damage . </P> <P> This effect is used to advantage in Zener diode regulator circuits . Zener diodes have a low breakdown voltage . A standard value for breakdown voltage is for instance 5.6 V . This means that the voltage at the cathode cannot be more than about 5.6 V higher than the voltage at the anode (although there is a slight rise with current), because the diode will break down--and therefore conduct--if the voltage gets any higher . This in effect limits the voltage over the diode . </P> <P> Another application of reverse biasing is Varicap diodes, where the width of the depletion zone (controlled with the reverse bias voltage) changes the capacitance of the diode . </P>

Pn junctions (or diodes) have three electrical contacts