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A tunnel diode is a semiconductor diode that exhibits negative resistance, meaning the current decreases with an increase in voltage. By making use of quantum mechanical effects, the tunnel diode is capable of fast operation and can function well into the microwave radio frequency band. The unique characteristics of tunnel diodes make them useful in applications such as oscillators and amplifiers.
Tunnel diodes are also known as Esaki diodes.
A tunnel diode is a two-terminal device with an n-type semiconductor acting as cathode and a p-type semiconductor acting as anode. It is heavily doped, which in turn creates a narrow depletion zone like a Zener diode. The current-voltage characteristic of a tunnel diode has a strong non-linear nature, as well as a negative differential resistance region.
Two distinct advantages of tunnel diodes are longevity and very high speed. A tunnel diode is capable of remaining stable over a longer duration of time than other semiconductor devices. It is also capable of high-speed operation and this is made use of in microwave radio frequency applications. Other benefits of using tunnel diodes include low power dissipation, low noise, simple fabrication and environmental immunity, meaning the tunnel diode is affected by the environmental temperature.
Disadvantages of tunnel diodes often include low peak-to-valley current ratio and reproducibility. Unlike other devices, the negative resistance region along with peak-to-valley current is not high, which is mostly required to match the performance that is possible in other similar devices. Reproducibility is also often impossible with tunnel diodes.
Tunnel diodes are not currently widely used, as there are other alternatives available.
Due to rapid tunneling action, a tunnel diode is used in very high frequency applications as there is no signal distortion and also less transit time effect. Tunnel diodes are also in used in high-speed switching owing to the tunneling action property.