In some materials (III-V compounds such as GaAs and InP), after an electric field in the material reaches a threshold level, the mobility of electrons decrease as the electric field is increased, thereby producing negative resistance.
The I-V curves of a Gunn diode will help explain the effect. For low voltages (up to 1 volt perhaps), the Gunn diode behaves nearly as a linear resistor. Then at some point the current stops increasing with increasing voltage. This is known as the threshold voltage. Above this point the diode has negative resistance (curve slopes downward), which mean that it is just itching to oscillate! The operating point is usually about 4X the threshold voltage.
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| Characteristics of Gunn Diode |
A two-terminal device made from such a material can produce microwave oscillations, the frequency of which is primarily determined by the characteristics of the specimen of the material and not by any external circuit. The Gunn Effect was discovered by J. B. Gunn of IBM in 1963.
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| J. B Gunn |
I hope this post will help the electronics beginners to understand Gunn Effect!
ReplyDeleteyes sir it is short and sweet
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