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What is a Tunnel Diode?

A tunnel diode (also known as a Esaki diode) is a type of semiconductor diode that has effectively “negative resistance” due to the quantum mechanical effect called tunneling. Tunnel diodes have a heavily doped  pn junction that is about 10 nm wide. The heavy doping results in a broken band gap, where conduction band electron states on the N-side are more or less aligned with valence band hole states on the P-side.

The application of transistor in a very high in frequency range are hampered due to the transit time and other effects. Many devices use the negative conductance property of semiconductor for these high frequency applications. A tunnel diode is one of the most commonly used negative conductance devices. It is also known as Esaki diode after L. Esaki for his work on this effect.

The concentration of dopants in both p and n region is very high, at around 1024 – 1025 m-3. The pn junction is also abrupt. For this reasons, the depletion layer width is very small. In the current voltage characteristics of tunnel diode, we can find a negative slope region when a forward bias is applied.

The name “tunnel diode” is due to the quantum mechanical tunneling is responsible for the phenomenon that occurs within the diode. The doping is very high so at absolute zero temperature the Fermi levels lies within the bias of the semiconductors.

Tunnel Diode Applications

Tunnel diode is a type of sc diode which is capable of very fast and in microwave frequency range. It was the quantum mechanical effect which is known as tunneling. It is ideal for fast oscillator and receivers for its negative slope characteristics. But it cannot be used in large integrated circuits – that’s why it’s an applications are limited.

When the voltage is first applied current stars flowing through it. The current increases with the increase of voltage. Once the voltage rises high enough suddenly the current again starts increasing and tunnel diode stars behaving like a normal diode. Because of this unusual behavior, it can be used in number of special applications started below