why the negative resistance occurs in the tunnel diode ?

please EXPLAIN the total operation of tunnel diode.

 

The negative resistance occurs because of Quantum Tunneling. In classical physics a charge particle can be trapped inside a potential well. That is another way of saying that it can only move in a confined region of space because it encounters a field with a potential function that prevents it from wandering around. Think of yourself trapped at the bottom of an empty water well with no way to get out.

Because atomic particles exhibit quantum behavior they can tunnel through the potential barrier and produce currents that are impossible in classical physics. Resistance can be viewed as the slope of any linear function that relates voltage and current.The region of negative resistance occurs when an increase in current is associated with a drop in voltage. this region of negative resistance occurs between two regions of positive resistance. The other interesting thing about them is that their reverse breakdown voltage is effectively 0 volts.

Wiki is your friend.
http://en.wikipedia.org/wiki/Tunnel_diode