The question asks to identify a specific type of properly doped crystal diode that exhibits a sharp breakdown voltage. Let's examine the options provided to determine which one fits this description.

Understanding Crystal Diodes and Breakdown Voltage

A crystal diode, also known as a semiconductor diode, is a two-terminal electronic component that conducts current primarily in one direction. When a reverse voltage is applied across a standard diode, only a very small leakage current flows until a certain high voltage is reached. At this point, called the breakdown voltage, the current increases rapidly. However, the breakdown in a standard diode can be destructive if the current is not limited.

Certain types of diodes are specifically designed to operate in the reverse breakdown region without being destroyed. These diodes are characterized by a precise and sharp breakdown voltage.

Identifying the Diode with Sharp Breakdown

Let's look at the options:

• Zener diode: A Zener diode is a special type of diode that is heavily doped compared to a regular diode. This heavy doping creates a narrow depletion region. When a reverse voltage is applied and reaches the Zener voltage (which is the breakdown voltage), a process called Zener breakdown or avalanche breakdown occurs, leading to a sharp and controlled increase in current. Zener diodes are designed to operate stably in this reverse breakdown region and are commonly used for voltage regulation because of their constant voltage characteristic once breakdown is reached.
• Zener voltage: This term refers to the specific voltage at which the Zener breakdown occurs in a Zener diode. It is a characteristic of the diode, not the diode itself.
• Zener current: This term refers to the current flowing through the Zener diode when it is operating in the Zener breakdown region. It is a flow of charge, not the diode itself.
• Zener burn out: This refers to the destructive failure of a Zener diode, usually due to excessive power dissipation when operating in the breakdown region without proper current limiting. It is a failure mode, not a type of diode.

Based on the characteristics described – a properly doped crystal diode with a sharp breakdown voltage – the term that specifically names this component is the Zener diode.

Why Zener Diode Fits the Description

The Zener diode is intentionally designed with specific doping levels to achieve a predictable and sharp breakdown voltage when reverse biased. This feature is the defining characteristic that distinguishes it from a standard diode in reverse bias operation and makes it useful for voltage regulation and reference applications. The term "sharp breakdown voltage" directly points to the intended operation of a Zener diode in its reverse breakdown region.

Therefore, a properly doped crystal diode which has a sharp breakdown voltage is known as a Zener diode.