Diode and Applications

A diode is formed when in a single piece of intrinsic semiconductor (eg: silicon materials), donors and acceptors atom are added.
Diodes are connected in series to enhance the PIV rating beyond the capability of individual diodes.
Diodes are connected in parallel to increase the current carrying  capability of the parallel stack beyond the capability of the individual diodes.

 
 
 
 
 
 
When no external voltage is applied, electrons from n-type material and holes from p-region diffuse randomly. Some of them negative ion moves in p-region where positive ion moves in n-region due to which there sets up a new charge empty region that tries to stop the flow of holes towards n-region and electrons into p-region. Only those electrons and holes having suggicient energy level penetrates the junction and help the charge empty region to build more potential .
Eventually, the potential increases to an amount that can stop the further movement of holes and electrons when no external when no external voltage is applied. This charge-empty region is called depletion layer and the potential developed across it is called barrier potential.
When circuit is reverse biased, negative terminal of battery is connected to p-side and positive to n-side. So, holes and electrons are attracted towards the opposite polarity. So, no current flows. But when, reverse voltage is increased, breakdown occurs producing large amount of charge carriers and a lot of reverse current flow.
In the case of forward bias, no current flows unless applied voltage is less than barrier potential. Once applied voltage overcomes the barrier potential , current flows smoothly.
Peak Inverse Voltage (PIV): It is the max voltage that can appear accross the diode without causing it any damage.