These are the material with resistivity between conductors and insulators. That is they are neither conductor nor insulator, therefore they are called Semi conductor. Examples, germanium has resistivity of 0.6×103Ω-m and silicon has resistivity of 1.5×103Ω–m
Semi conductors are grouping IV, elements, with four electrons in their outmost shell. The valence electrons of semi conductor are not wholly free throughout the volume of semi conductor, but participate on covalent bond that hold the atom of semi conductor together and consequently they cannot move about freely
When all the valence electrons are held in covalent bonding, no charge carriers are free to move and hence there will be no conduction, most of the covalent bonds are like this, except for diamond with conductivity of 10-18(Ω-m)-1 , pure silicon at 290k which has the conductivity of 0.3×10-7((Ω-m)-1), and germanium that has conductivity of 0.2×10-3((Ω-m)-1). Since element mentioned above do not have zero conductivity, therefore there must be electrons that are free which participate in conduction. This means that covalent bond is incomplete in them
When the temperatures of semi conductors are increased, the conductivities increase due to holes and electrons pair production. Electrons and holes are negative and positive charges respectively produced when the temperature of a semi conductor is increased. These charges are produced because of broken bond when temperature is increased, due to broken bond, which give rise to free electrons called negative charges and consequently give rise to holes called positive charges in semi conductors
In semi conductor, there is n-type and p-type
Pure semi conductors do not conductor current very well because of limited number of electrons in the conduction band, and in addition they require that electrons and holes be present in exact equal number. Note that electron and holes are produced in pairs and also disappear in pairs
N-type semi conductor
This type of semi conductor is produced when impurities called donor s are added to them. The donor impurities are element of group V in periodic table .When the impurity is added to semi conductor it consequently contributes conduction electrons to the semi conductor without contributing holes. The semi conductors doped in this way are called n-type (negative type). In this type of semi conductor the electrons are majority carriers while holes are the minority carriers
P-type semi conductor
In this type of semi conductor, impurities are added to contribute holes instead of electrons. The impurities are group III elements in periodic table which accept electrons to give rise to more numbers of holes than electrons and therefore they are called acceptors .So in p-type semi conductor holes are the majority carriers, while electrons are minority carriers
Example of dopants (impurities) use for either n-type of p-type semi conductors are ,Phosphorus, Boron, arsenic and gallium
Intrinsic and Extrinsic semi conductors
Intrinsic Semi conductor
An intrinsic semiconductor can also be called undoped semi conductor or I-type semi conductors. It is a pure semi conductor without any impurities added to it. The number of charged carriers is determining by the properties of semi conductor itself instead of impurities. In intrinsic semi conductor the number of excited electrons and the number of holes are equal. The term intrinsic here differentiate between the properties of pure silicon and the properties of doped n-type and p-type semi conductors
Extrinsic semi conductors
Extrinsic semi conductors are the ones that have been doped or impurities have been added to them, to make it perform better. In extrinsic semi conductors, electrical properties are being governed by the impurities in them. So both N-type and p-type semi conductors are extrinsic semi conductors
Example of elements that can be used as semi conductors, are Diamond, Silicon, germanium and many more.
What are the uses of semi conductors?
Semi conductors are the foundations of modern day’s electronics such as radio, computer, television, and mobile phones. Semi conductors are also use in manufacturing electrical components. It is used in electronic devices such as transistors, solar cells, diodes, switching device for the control and conversion of electrical power. Semi conductor is used in miniaturization of electric component. Integrated circuits are also products of semi conductors
Note also that electronics products such as phones, televisions, radio set, and many more are affordable to both poor and the rich because of semi conductor.