The Gunn effect, named after physicist J. B. Gunn who discovered it in 1963, is a phenomenon observed in certain semiconductor materials, particularly in gallium arsenide (GaAs) and other compound semiconductors.

In materials exhibiting the Gunn effect, when subjected to a high electric field, the conductivity can exhibit negative differential resistance (NDR). This means that as the voltage across the material increases, the current flowing through it decreases, which is contrary to Ohm’s law.

The phenomenon arises due to the interaction between electrons and the lattice structure of the semiconductor material. When a high electric field is applied, electrons gain enough energy to overcome the lattice potential and accelerate through the material. However, at a critical electric field strength, the electrons experience a phenomenon called “velocity saturation,” where their velocity becomes constant despite the increasing electric field. This leads to a decrease in drift velocity and hence a decrease in current, resulting in the negative differential resistance behavior.

The Gunn effect finds applications in devices such as Gunn diodes, which exploit this behavior to generate microwave oscillations. In a Gunn diode, the negative resistance region of the current-voltage characteristic is used to create an oscillator circuit capable of generating microwave signals. Gunn diodes are commonly used in microwave devices, radar systems, and other high-frequency applications.

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