A semiconductor is a material that has an electrical resistance between that of a conductor and an insulator. Semiconductor materials also contain 4 electrons in their outer electron shell (valence shell).
Most group 14 elements in the periodic table can be semiconductors, these are carbon, silicon and germanium, most modern semiconductor components are made from silicon that has been grown into a cubic crystal structure.
The arrangement of atoms in the semiconductor is very important, semiconductors must have a cubic crystal structure to function properly, pure silicon or germanium is never used to manufacture working semiconductor components as its resistance cannot be controlled very well, it is only effected by changes in temperature.
In a pure semiconductor all the high energy outer electrons are used up maintaining the tight crystal structure save for those dislodged thermally.
P and N type Semiconductors
Two different types of semiconductor can be made by adding tiny amounts of impurities to the semiconductor material in a process known a doping, one type of semiconductor is the P type which is made by adding a small amount of boron.
Boron (B) is a group 13 element, it had 3 electrons in its outer shell, so when it is added to the crystal structure it leaves a gap known as a ‘hole’, because of this it is known as an acceptor impurity because the hole can accept an electron.
The other type is the N type semiconductor which is doped with phosphorus (P) which is a group 15 element that has 5 electrons it its outer shell, when added to the crystal structure it leave a free electron, thus it is known as a donor impurity.
A hole is an empty space in the crystal lattice that can accept an electron to fill the gap, holes cannot move as such, however they may appear to do so as electrons in the semiconductor move around.
P type semiconductors have many holes and few electrons, thus holes are the majority charge carrier with electrons being the minority.
The reverse is true with N type semiconductors, electrons are the majority charge carrier with holes as the minority.
Placing a piece of N and P type semiconductor results in diffusion, where some of the electrons in the N material jump over to fill some holes in the P material, this results a small region forming in each type.
In the P type semiconductor a small N type area is formed where the materials touch.
In the N type semiconductor a small P type area is formed where the materials touch.
Depletion Region
This results in a very small region forming in the semiconductor known as the depletion region, this region is very important in the manufacture of useful semiconductor components as they are all made up of both P and N type material.
The simplest electronic device made from semiconductors is the diode which is made of one P type and one N type semiconductor material sandwiched together, this results in a depletion region forming a P-N junction.
I will add more information on how diodes work in my next post.
Posted by chryseus8086 
