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Semi conductor

A semiconductor is that material, whose conductivity lies between conductor is an insulator with an energy gap of about 1ev(electron volt). The most common materials used as, semiconductors are germanium (Ge) and silicon(Si) because of their property enhanced high temperature. i.e the change in energy gap with changing temperature there will be no significant.

An energy gap in between conductors and insulators. This gap is typically more or less 1 eV, thus one electron requires energy more than conductors but less than insulating materials for shifting valence band to conduction band. At low temperature there are very less number of electrons in conduction band in a semiconductor but if temperature increases electron jumps to valance band.

Semiconductors are two types

  • Intrinsic semiconductor
  • Extrinsic semiconductor

Intrinsic semiconductor

In intrinsic semiconductors are those materials in which purity atoms doping. i. e An intrinsic semiconductor in which no other materials is intentionally dopped. The conductivity of intrinsic semiconductor is more than that of a pure semiconductor as the impurities provide a few energy levels in the band gap.

Intrinsic semiconductor are pure semiconductor. i . e that semiconductor there is no impurities atoms, . this types semiconductor are pure in nature.

In intrinsic semiconductors in 14 groups are element in periordic table is a silicon (Si) are doping . it totally depend on temperature . i. e at absolute zero temperature conductivity also zero.

Properties of intrinsic semiconductor

Many types properties are holds in intrinsic semiconductor given as below.

  1. It behaves as an insulator at absolute zero temperature.
  2. Electrons are excited by thermal energy.
  3. The conductivity of intrinsic semiconductor is pured atoms.

Law of mass action intrinsic semiconductors

According to the law of mass action ,

ni2 = ne . nh

Ni = intrinsic Semiconductor.

Ph = hole concentration.

ne = electron concentration

Intrinsic semiconductor ni = ne = Ph

Extrinsic semi conductor

its is some impurity atoms doping in which those materials. This is a semiconductor in which certain impurities atoms are dopped. The addition of these impurities atoms is knowns as dopants to semiconductor largely increases the conductivity of semiconductors. This process is shows as doping of semiconductor. In extrinsic semiconductor pure semiconductors is highly doping in impurities atoms.

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Properties of extrinsic semiconductor

Many types of properties in extrinsic semiconductors are holds.

  1. The dopants are usually either third groups or fifth group elements . for example As ,Sb , B , In etc.
  2. An impurities added is of very small magnitude.
  3. Extrinsic semiconductors are pure semiconductors than conduct at room temperature.

Extrinsic semiconductor are two types:-

  • p type extrinsic semiconductor
  • n type extrinsic semiconductor

P type extrinsic semiconductor

p-type semiconductor is an extrinsic semiconductors. When a trivalent impurity like Boron, Aluminum, Indium etc is adding to an intrinsic or pure semiconductor like as silicon or germanium. It is shows that as p-type semiconductor. Trivalent impurities such as boron (B), gallium (Ga), indium (In), aluminum (Al) etc. It is known as acceptor impurity. An Ordinary semiconductors is made materials which is not carry an electric current.   but are not highly resistant to doing so. They fall half way between conductors and insulator.

An electric current occurs when an electron moves through the material all to move, there must be an electron ‘hole’ in the material for the electron to move into. A p-type semiconductor has more holes than electrons. This allows the current to flow along with the material from hole to hole but only in one direction.

N type extrinsic semiconductor

An n-type semiconductor is an intrinsic semiconductor doping with phosphorus (P), arsenic (As), or antimony (Sb) as an impurity. Silicon of Group IV has four valence electrons and Arsenic of Group V has five valence electrons. If a small amount of Arsenic(As) is add to a pure silicon crystal, one of the valence electrons of Arsenic becomes free to move around (electron) as a surplus electron. When this electron is attracted to the “+” side and moves, current flows.

any element requires eight electrons at its outermost orbit. But it is also true that all atoms do not have eight electrons at their outermost orbit. But all the atom have an requires to have eight electrons at their outermost orbit.

The electrons at an outermost orbit of an atom is known as valence electrons. If the outermost orbit of an atom is not eight electrons, then there will be more vacancies as the deficiency of electrons in orbit. These vacancies are accept electrons to complete eight electrons in the outermost orbit of the atom.

The mostly uses semi conductors are silicon and germanium. The Silicon has 14 electrons which is configures 2, 8, 4. Germanium has 32 electrons which is configuration as 2, 8, 18, 4. these two semiconductors have 4 electrons at their outer-most orbit. Hence, there are vacancies for more 4 electrons.

Four valence electrons completed these vacancies each of which is from four separately existence semiconductor atom. Accordingly all atoms of a semi conductor crystals make a covalent bond which is nearest most existence atoms. Ideally, all valence electrons in a semiconductor crystal are involving in forming of covalent bonds. Hence, there should not be any free electron in the element.

Conductivity of semiconductor

But this is not the actual case. At absolute 0o Kelvin there is no any free electron in these element, but when the temperature increases absolute zero to room temperature, numbers of valence electrons in the bonds are thermally excited and come out from the bond and generate a number of free electrons in the crystal. These free electrons reason of the conductivity of semiconductors materials at any temperature higher than absolute zero.

There is a method of increasing conductivity of semiconductors at any temperature greater than absolute zero. This method is known as doping. In this method is pure or intrinsic semiconductor are doping with pentavalent impurities like arsenic . These impurity atoms replace some of the semiconductor atoms in the crystal and occupy their positions. As the impurity atoms have five valence electrons in the outermost orbit. these four atoms will create the covalent bond with four adjacent semiconductor atoms.

Conclusion of semi conductor

Basically all of given topics are in semi conductor explanation.

To reads all topics very carefully you must have beneficial. Because they very good topic in exam point of view.

As much as given topics makes very easily.