What is a pn junction that is designed to operate in the reverse bias breakdown region?

The pn junction that is specifically designed to operate in the reverse bias breakdown region is the Zener diode. Zener diodes are engineered to allow reverse current to flow when the voltage across the junction exceeds a predetermined value known as the Zener breakdown voltage. This characteristic makes them particularly useful for voltage regulation applications, where they can maintain a constant output voltage despite variations in input voltage or load conditions.

The unique construction of a Zener diode allows it to handle the reverse breakdown without damage, making it a reliable component in circuits designed for stabilizing voltage. When the voltage reaches the Zener voltage, the diode enters breakdown mode, conducting current while keeping the voltage across it stable.

Other types of diodes, such as Schottky diodes and rectifier diodes, do not exhibit this characteristic behavior in reverse bias. Schottky diodes are primarily used for their fast switching speeds and low forward voltage drop, and rectifier diodes are usually employed for current rectification but are not intended for Zener operation. Bipolar junction transistors serve different functions entirely, as they are multi-terminal devices used primarily for amplification and switching.