Avalanche effect

The greater the reverse bias voltage, the “more determined an insulator” a P-N junction gets—to a point. If the reverse bias goes past this critical value, the voltage overcomes the ability of the junction to prevent the flow of current, and the junction conducts as if it were forward biased. This avalanche effect does not ruin the junction (unless the voltage is extreme); it’s a temporary thing. When the voltage drops back below the critical value, the junction behaves normally again.
Some components are designed to take advantage of the avalanche effect. In other cases, avalanche effect limits the performance of a circuit.
In a device designed for voltage regulation, called a Zener diode, you’ll hear about the avalanche voltage or Zener voltage specification. This might range from a couple of volts to well over 100 V. It’s important in the design of voltage-regulating circuits in solid-state power supplies; this is discussed in the next chapter.
For rectifier diodes in power supplies, you’ll hear about the peak inverse voltage (PIV) or peak reverse voltage (PRV) specification. It’s important that rectifier diodes have PIV great enough so that avalanche effect will not occur (or even come close to happening) during any part of the ac cycle. Otherwise, the circuit efficiency will be compromised.