Introduction

The tunnel diode is that the contact device that exhibits negative resistance. which means once the voltage has accumulated the present through it decreases. Classically, a carrier should have the energy a minimum of adequate to potential-barrier height to cross the junction.But consistent with quantum physics, there’s the finite likelihood that it will penetrate through the barrier for a skinny breadth. This development is termed tunneling and thus the physicist Diode is thought as Tunnel Diode.

Electron Tunneling in the p-n junction

• When the p and n region is extremely doped, the depletion region becomes terribly skinny (~10nm).
• In such case, there’s a finite likelihood that electrons will tunnel from the physical phenomenon band of n-region to the valence band of p-region.
• During the tunneling, the particle ENERGY doesn’t an amendment

Tunnel Diode Operation

When the semiconductor is incredibly extremely doped (the doping is bigger than No) the Fermi level goes higher than the conductivity band for n-type and below valence band for p-type material. This square measure is known as degenerate materials.

Under Forward Bias

Step 1: At zero bias there is no current flow

Step 2: A small forward bias is applied. Potential barrier continues to be terribly high – no noticeable injection and forward current through the junction. However, electrons within the physical phenomenon band of the n region can tunnel to the empty states of the valence band in p region. this may produce a forward bias tunnel current.

Step 3:  With a bigger voltage the energy of the bulk of electrons within the n-region is adequate to that of the empty states (holes) within the valence band of p-region; this may manufacture most tunneling current.

Step 4: As the forward bias continues to extend, the number of electrons within the n aspect that area unit directly opposite to the empty states within the valence band (in terms of their energy) decrease. so decrease within the tunneling current can begin.

Step 5: As a lot of forwarding voltage is applied, the tunneling current drops to zero. however, the regular diode forwards current because of electron-hole injection will increase because of a lower potential barrier.

Step 6: With further voltage increase, the tunnel diode I-V characteristic is similar to that of a regular p-n diode.

Tunnel Diode Operation

Under Reverse Bias

In this case the, electrons within the valence band of the p facet tunnel directly towards the gift of the empty state within the physical phenomenon band of the n facet making massive tunneling current that will increase with the appliance of reverse voltage. The TD reverse I-V is comparable to the Zener diode with nearly zero breakdown voltage.