Question 5.221: Explain the concept of tunnel diode?...

Tunnel diode, as shown in Figure 5.74, is a type of semiconductor 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 oscillators and receivers for its negative slope characteristics. But it cannot be used in large integrated circuits – that’s why it’s an application that is limited.

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. This diode is a two-terminal device. The concentration of dopants in both p and n region is very high. It is about 1024 – 1025 m-3 the P-N junction is also abrupt. For such reasons, the depletion layer width is very small. In the current-voltage characteristics of the tunnel diode, we can find a negative slope region when a forward bias is applied.

Quantum mechanical tunneling is responsible for the phenomenon and thus this device is named as tunnel diode. The doping is very high so at absolute zero temperature, the Fermi levels lie within the bias of the semiconductors. When no bias is applied any current flow through the junction.