Which of the following diodes is represented by the given symbol?

Explanation:

Varactor Diode:

• It is represented by a symbol of diode terminated in the variable capacitor as shown below:

• Varactor diode refers to the variable Capacitor diode, which means the capacitance of the diode varies linearly with the applied voltage when it is reversed biased.
• The junction capacitance across a reverse bias pn junction is given by

​           \(C=\frac{A\epsilon}{W}\)

• As the reverse bias voltage increases, the depletion region width increases resulting in the decrease in the junction capacitance.

PN Junction Diode:

• A unilateral device is a device that conducts only in one direction.
• p-n junction diodes conduct only when the p region is connected to higher voltage and n region is connected to lower voltage.
• When reverse biased, it acts as an open circuit.
• The symbol for a diode is as shown:

Schottky Diode: It is not a typical diode because it does not have a p-n junction.

It consists of a doped semiconductor (usually n-type) and metal, bound together as shown:        

Features:

• ​An important characteristic of a Schottky diode is its fast switching speed, as it doesn't allow the diode to reach saturation.
• This makes the Shottky diode useful for high-frequencies and digital applications.
• Schottky diode is also known as the Schottky barrier diode, surface barrier diode, majority carrier device, hot-electron diode, or hot carrier diode.
• Its symbolic representation is as shown:-

Tunnel Diode:

Symbol:

• It is a highly doped PN Junction diode, used for low voltage high-frequency switching applications.
• It works on the tunneling principle.
• When compared to a normal p-n junction diode, the tunnel diode has a narrow depletion width.
• In normal forward-biased operation, it exhibits the “Negative resistance region” as shown:
• The negative differential resistance in their operation, allows them to be used as oscillators, amplifiers, and switching circuits.
• Their low capacitance allows them to function at microwave frequencies.​