Semiconductor doping
Extrinsic semiconduction is achieved by introducing impurities, by doping, which greatly increases the conductivity of intrinsic semiconductors.
As the formation of band gaps is due to the regularity of the crystalline structure, any perturbation of this structure tends to create accessible states within these band gaps, making the gap more 'permeable'. Doping consists of implanting correctly selected atoms (called "impurities") inside an intrinsic semiconductor in order to control its electrical properties.
The doping technique increases the density of carriers within the semiconductor material. If it increases the density of electrons, it is called N-type doping. If it increases the density of holes, it is called P-type doping. Materials doped in this way are called extrinsic semiconductors.


Complément :
Fondamental :
The P-N junction forms the basis of the electronic component known as a diode, which only allows electric current to flow in one direction. Similarly, a third region can be doped to form double N-P-N or P-N-P junctions, which form bipolar transistors. In this case, the two semiconductors of the same type are called the emitter and the collector.


Complément :
N-type doping involves increasing the electron density in the semiconductor. This is achieved by including a certain number of electron-rich atoms in the semiconductor.
P-type doping increases the density of holes in the semiconductor. This is achieved by including a number of electron-poor atoms in the semiconductor to create an excess of holes.
A P-N junction is created by bringing an N-doped semiconductor into contact with a P-doped semiconductor. The junction causes the Fermi levels to equalise by shifting the bands. If a positive voltage is applied on the P side, the positive majority carriers (holes) are pushed towards the junction. At the same time, the negative majority carriers on the N side (the electrons) are attracted towards the junction.

