Semiconductors – Geeksgood

 

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Doping

Doping is the process of adding impurities to a pure semiconductor called “doping”. During doping, many semi-conductive devices are fabricated. Doping will increase the conductivity property of the material. And the doping also decreases the conductivity of the semiconductor. The conductivity of the material can be controlled by doping.

Internal semiconductor

The pure form of a semi-conductor is called an internal conductor.

Ex: Let us consider the structure of Si. A silicon atom has 14 and 4 valence electronics in Si that are shared by four neighboring atoms in crystal regions. Due to the lack of free electronics at full temperature at 0 k, it is a pure intrinsic semiconductor.

Conductivity is also increased by increasing the concentration of free electrons and the temperature of the pores. When an electric field is applied the free electrons are carried from space to the positive potential of the negative, resulting in the flow of free electrons from the negative electrons. Negative potential due to movement of bound electrons in the opposite direction traveling from positive to positive. This causes a hole from positive to negative potential.

Net current = free electron current + hole current

J = J (N) + J (P)

P = n = n (i) for pure semi conductor

n (i) is the carrier concentration.

The current conduction in the inner semiconductor is enhanced by adding a small amount of impurity to the inner semiconductor. Then the inner semiconductor becomes an external semiconductor. The conductivity of the inner semiconductor can be increased by converting it to an external semi-conductor through the doping process.

External semi-conductors are classified into two groups based on the number of holes and electrons they possess.

-> N-Type Semi Conductor

-> P-Type Semi Conductor

N-type semi conductor

If the added impurity is a pentavalent atom, then the resulting semi conductor is called an n-type semi conductor.

Ex: Nitrogen, Phosphrous, Aresinic

Ph and As are commonly used pentavalent impurities. N is rarely used, impurities due to its low tendency to donate an electron with a less filled electronic configuration. Bi and Et are heavy metals so they are not used for the doping process. Addition of pentavalent impurities will create an energy level slightly below the conduction band. This is called the donor energy level.

The difference between the donor energy level and the conduction energy level is called ionization energy. This energy will be stored as heat. Electrons present in the donor energy level will be moved to the conduction band to reduce the number of holes in the conduction band. Which increases the number of electrons with respect to the number of holes. Therefore the concentration of electron density will be higher than the concentration of hole density.

P-type semiconductor

If the added impurity is the ternary atom then the semiconductor is called the p-type semiconductor. Boron, aluminum, gallium are examples of aromatic impurities added to form peat-type semiconductors. Boron is often used as a pungent impurity due to its abundance on Earth. The addition of the trident impurity will create an empty energy level just above the valence band. There will be holes in the empty energy band. Which will increase the number of holes. So the concentration of hole density will be higher than the concentration of electron density.


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