A complete guide to Diodes

The most widely used circuit element is diode without which many electronic gadgets wouldn't even exist.Now before I begin my lecture on Diode,you must have some preliminary knowledge about semiconductors because a diode is a fusion of semiconductor materials(namely p and n type semiconductors).So,let's start by defining what is a semiconductor?The most common definition you will find is that semiconductor is a material whose conductivity lies between that of a conductor and a insulator.Now, to fully understand the characteristics of a semiconductor it will take a hell lot of time but I will give brief insight so that you have no difficulty in understanding Diode.
SEMICONDUCTOR-

The above diagram is known as the energy band diagram of a semiconductor.Now as you can see from the above image the two energy bands are distinctly separate as there is no overlapping.The empty space between the conduction band and that of valence band is known as forbidden band gap which is roughly 1 eV for a semiconductor.The forbidden gap is an important characteristic or you can say a tool that can predict that a given material is semiconductor,conductor or a insulator.

At absolte zero of temperature,no electrons have the energy to cross the forbidden gap and reach the conduction band but however at room temperature these electrons get enough thermal energy that is greater than the band gap energy to cross the gap and to reach their destination.Thus you can see that this material behaves as a insulator at absolute zero but as a conductor at room temperature.This specific property enables the crystal to differentiate it as the semiconductor.Higher the temperature higher are the chances of electrons to jump to conduction band and so greater is the conductivity.There is also one thing you should know that when electrons leave their postions in the valence band,it leaves some energy level as unfilled.So,these unfilled levels are termed as holes.This are a sort of positive charge carriers and any movement of these carriers will be termed as positive charge moving from one place to another.

Now there are two types of semiconductors -one is intrinsic and the other one is extrinsic.

Intrinsic semiconductor is the pure form of semiconductor and the above explanation is enough to understand intrinsic semiconductor.The real fun begins in extrinsic semiconductor which you must and should learn so as to master Diode completely.

EXTRINSIC SEMICONDUCTOR-This the impure form of semiconductor where doping is introduced.Now let me define Doping for you-"Doping is the process by which impurity in the form of semiconductor atoms is introduced to influence the electrical characteristics of the material".Due to different types of doping two types of  extrinsic semiconductor are available that is p-type and n-type material.

n-type material- 

When a semiconductor such as Silicon and Germanium is doped with pentavalent impurity (Phosphorus,Antimony,Arsenic) we get n-type material.The above diagram is the crystal structure of n-type material .As seen from the figure four out of five electrons occupy covalent bonds.The fifth electron as you can see is loosely bound.The energy required to detach this electron is almost negligible and this energy is easily provided by the thermal agitation of crystal.So, these fifth electron can move freely .When these fifth electron is transferred to the conduction band ,the parent impurity atom becomes positively charged immobile ion.So, in these way each impurity atom donates a free electron to the semiconductor thereby influencing electrical characteristics.This type of semiconductor is also called donor type semiconductor.Here you will also observe that the no. of electrons increase where the holes are in a state of decline.So in an n-type material,electrons are the majority charge carriers and holes fall in the minority group.

p-type semiconductor- 

When silicon and germanium is doped with trivalent impurity(Gallium,Boron),we get p-type semiconductor.The above image shows the crystal structure of p-type.The impurity atom allows electrons to fill only three covalent bonds .The vacancy that exists in the fourth bond constitutes a hole.So,this hole is deliberately created with the purpose that it would accept electrons from the neighbourhood.And when it does a hole is created at that position and this is bright shining example of hole moving from one place to another (+ve charge) as i have mentioned this in my post previously.This is also called acceptor which is justified by the above facts.In a p-type semiconductor holes are the majority and electrons are the minority charge carriers .

The above two facts about majority and minority in both the type of semiconductors forms the basis of understanding Diodes.The full explanation of working of diodes will be mentioned in my next post.Until then Happy Reading.Do bring to my notice if something is wrong!!!!