Question 5.222: Explain the characteristics of the tunnel diode?...

When a reverse bias is applied the Fermi level of the p-side becomes higher than the Fermi level of the n-side. Hence, the tunneling of electrons from the balance band of the p-side to the conduction band of the n-side takes place. With the interments of the reverse bias, the tunnel current also increases.

When a forward bias is applied to the Fermi level of the n-side becomes higher than the Fermi level of the p-side, thus the tunneling of electrons from the n-side to the p-side takes place. The amount of the tunnel current is very large than the normal junction current. When the forward bias is increased, the tunnel current is increased up to a certain limit.

When the band edge of the n-side is the same as the Fermi level in the pside, the tunnel current is maximum with the further increment in the forward bias the tunnel current decreases and we get the desired negative conduction region. When the forward bias is raised further, normal PN junction current is obtained which is exponentially proportional to the applied voltage. The V-I characteristics of the tunnel diode are given

The negative resistance is used to achieve oscillation and often Ck+ function is of very high-frequency frequencies.