p-n junction diode

Previously,I have mentioned that a diode is a fusion of p and n-type semiconductors,p and n-type materials taken separately has no practical value but when they are combined they give rise to new devices such as transistors,diodes etc.A diode is a device which allows the current to flow in one direction but disallows the reverse.To understand the working you must have the basic knowledge of semiconductors,so here's the link which will help you to do that  http://dutta60.blogspot.in/2014/07/a-complete-guide-to-diodes.html .

The first image is the symbol for p-n junction diode while the other two is how it looks like in real life.
What happens when p and n type semiconductors are clubbed together?
                                     

Sorry for the bad drawing,so as I was saying,the p-region(left portion of the image) has holes which are mobile and negetively charged impurity ions which are immobile whereas the n-region(right side) has positively charged impurity ions which are immobile and free electrons which are mobile.

MOTION OF MAJORITY CHARGE CARRIERS- When the p-n junction is formed diffusion of holes begin from p-region to the n-region and similarly the diffusion of electrons happens on the reverse direction on account of difference in concentration.The movement of both  the holes and electron produces a diffusion current directed from left to right.

Formation of depletion region- one thing that happens during the formation of diffusion current is that recombination takes place near the junction(marked by yellow in the above image) thereby eliminating a hole and an electron in the process.Thereby,leaving uncompensated positive donor ions in the n-region and negetive acceptor ions in the p-region forming the so-called DEPLETION REGION.After this is formed no more diffusion can take place as holes and electrons are both repelled respectively unless some biasing is done (it will be taken up in my next post).The depletion region is also known as space charge region.