Gunn Diode

The Gunn diode is a type of semiconductor device that is widely used in high-frequency
applications, particularly in microwave technology. This document provides an overview of
the Gunn diode, including its working principle, characteristics, applications, and advantages
over other types of diodes. Understanding the Gunn diode is essential for those involved in
electronics and communication engineering, as it plays a crucial role in the development of
oscillators and amplifiers.

Understanding the Gunn Diode

Working Principle
The fundamental operation of the Gunn diode

Characteristics
Key features and properties of the Gunn diode

Applications
Practical uses of the Gunn diode in technology

Advantages
Benefits of using Gunn diodes over other diodes

Gunn Diode – Symbol, Construction, Working and

A Gunn diode is a type of diode having two terminals with negative resistance used for its
very high switching speed. Though it is not considered a diode since it does not contain a
conventional PN junction but is made of a single N-type semiconductor. It is why it is known
as a Transfer Electron Device “TED“.
It can conduct in both directions, therefore it can’t be used for rectification. It is termed a
diode because it has two terminals anode and cathode.
It works on the principle of ‘Gunn effect’. The phenomenon is named after British physicist
John Battiscombe Gunn (J.B. Gunn) who discovered it in 1963. He observed that after
applying very high voltage to a very thin layer of semiconductor, high-frequency oscillations
are generated.

Analyzing Gunn Diode Characteristics

Structure Materials

Understanding
Single N-type
Gallium Arsenide Gunn Diode
Semiconductor
Functionality

Lack of PN Junction Gallium Nitride

High Voltage
Frequency Generation
Application

Gunn Effect High-Speed Switching

Operating Principle Applications

It is usually made of gallium arsenide GaAs whose operating frequency reaches up to 200
GHz and gallium nitride GaN, Gunn diode’s operating frequency reaches up to 3 THz.

Working Principle

The Gunn diode operates based on the principle of negative differential resistance. It is made
from n-type semiconductor materials, typically gallium arsenide (GaAs) or indium phosphide
(InP).
When a voltage is applied across the diode, it can exhibit a region where an increase in
voltage results in a decrease in current, leading to the generation of microwave oscillations.
This behavior is due to the transfer of electrons between different energy bands within the
semiconductor material.
 Understanding Gunn Diode Operation

Negative
Semiconductor
Differential
Materials
Resistance

Voltage
Current Behavior
Application

Microwave
Electron Transfer
Oscillations

Construction

The Gunn diode is made of only an N-type semiconductor because the transferred electron
effect (explained below) only occurs in N-type materials and it does not occur in P-type
materials because it is only appropriate for electrons and not holes.
The materials used for Gunn diode are Gallium Arsenide (GaAs), Gallium Nitride (GaN), Indium
Phosphide (InP), Indium Arsenide (InAs), Indium Antimonide (InSb), Cadmium Telluride (CdTe),
Cadmium Sulphide (CdS) and Zinc Selenide (ZnSe). All these materials have electrons as
majority carriers.

Gunn Effect

The Gunn effect was discovered by J.B. Gunn in 1963. In certain semiconductor materials such
as gallium arsenide GaAs and indium phosphide InP has two valleys in its conduction band
based on their mobility, the lower valley and upper valley. There is a small energy gap
between the two valleys.
Electrons initially reside in the valance band. After gaining certain energy equal to the
forbidden energy gap between the valance band and conduction band, the electrons jump
to the conduction band. At first, the electrons are in the lower valley where the electrons
have very small effective mass and high mobility. The semiconductor behaves ohmically i.e.
the current increases with an increase in the voltage.

As the energy gained by the electrons in the lower valley increases, they jump to the upper
valley where the electrons have large effective mass and low mobility. Therefore if the
electrons move to the upper valley due increase in the applied voltage, the current through
the semiconductor decreases. This electron transfer between the two valleys is known as the
transferred electron effect or Gunn effect named after the physicist who discovered it.

V-I Characteristics
The VI characteristics curve shows the relationship between the voltage and current through
the Gunn diode in the given figure below.

As evident from the graph, the current initially increases with an increase in the applied
voltage up to the threshold voltage Vth. Once the voltage goes beyond Vth, the current
starts to decrease as shown by the negative slope in the graph. This region is known as the
negative resistance region. The Gunn diode is utilized in this region to generate
high-frequency oscillation and also amplify the signals.
The current decreases down until the valley point. Further increase in the voltage increases
the current again.

Characteristics
1. Negative Differential Resistance: The most notable characteristic of the Gunn diode is
its ability to exhibit negative differential resistance, which is essential for generating
oscillations.
2. Frequency Range: Gunn diodes can operate at frequencies ranging from a few
gigahertz to several hundred gigahertz, making them suitable for microwave
applications.
 3. Power Output: They can produce significant power output, which is beneficial for
various applications in communication systems.

4. Temperature Sensitivity: The performance of Gunn diodes can be affected by

Applications

Gunn diodes are utilized in various applications, including:

• Microwave Oscillators: They are commonly used in microwave oscillators for radar
systems and communication devices.
• Amplifiers: Gunn diodes can be used in amplifiers to boost signal strength in
microwave communication systems.
• Frequency Generators: They serve as frequency generators in various electronic
devices, providing stable frequency outputs.
• Sensors: Gunn diodes are also employed in certain types of sensors, particularly in the
detection of gas and other substances.

Gunn Diode Applications

Microwave
Oscillators Amplifiers
Used in radar systems Boosts signal strength
and communication in microwave
devices. communication.

Frequency
Generators Sensors
Provides stable Detects gases and other
frequency outputs for substances effectively.
electronic devices.

Advantages
• High Efficiency: Gunn diodes are known for their high efficiency in converting
electrical energy into microwave energy.
• Compact Size: Their small size makes them suitable for integration into compact
electronic systems.
• Wide Frequency Range: They can operate over a broad range of frequencies, making
them versatile for different applications.
Conclusion

The Gunn diode is a vital component in the field of microwave technology, offering unique
characteristics that enable its use in various high-frequency applications. Its ability to
generate oscillations through negative differential resistance makes it an essential device for
engineers and technologists working in communication systems and electronic devices.
Understanding the Gunn diode's principles and applications is crucial for leveraging its
capabilities in modern technology.