Tag: impurity defects

The addition of small amount of foreign impurity in the host crystal is called as doping. It results in an increase in the electrical conductivity of the crystal. Doping of group 14 elements (such as Si, Ge etc.) with elements of group 15 (such as As) produces an excess of electrons in the crystals and thus, gives n-type semiconductors. Doping of groups 14 elements with group 13 elements (such as Indium) produces holes (electron deficiency) in the crystals. Thus, p-type semiconductors are produced. The symbol 'p' indicates flow of positive charge. Also, the band gap in germanium is small as Ge is a semi-conductor.

The addition of a small amount of foreign impurity in the host crystal is called doping. 

The addition of small amount of foreign impurity in the host crystal is called as doping. It results in an increase in the electrical conductivity of the crystal. Doping of group 14 elements (such as Si, Ge etc.) with elements of group 15 (such as As) produces an excess of electrons in the crystals, thus, giving n-type semiconductors. Doping of groups 14 elements with group 13 elements (such as Indium) produces holes (electron deficiency) in the crystals. Thus, p-type semiconductors are produced. The symbol 'p' indicates flow of positive charge. Positive holes are responsible for the semiconducting properties like conduction.

A compound may have excess metal ion if an anion (negative ion) is absent from its appropriate lattice site creating a 'void' which is occupied by an electron. The ionic crystal which is likely to possess Schottky defect may also develop this type of metal excess defect. When alkali metal halides are heated in an atmosphere of vapours of the alkali metal, anion vacancies are created. The anions (halide ions) diffuse to the surface of the crystal from their appropriate lattice sites to combine with the newly generated metal cations. The electron lost by the metal atom diffuse through the crystal is known as F-centres. The main consequence of a metal excess defect in the development of colour in the crystal. For example, when NaCl crystal is heated in an atmosphere of Na vapours, it becomes yellow. Similarly, KCI crystal when heated in an atmosphere of potassium vapours, it appears violet.
The addition of a small amount of foreign impurity in the host crystal is called doping. It increases the electrical conductivity of the crystal. Doping of group 14 elements (such as Si, Ge etc.) with elements of group 15 (such as As) produces an excess of electrons in the crystals, thus, giving n-types semiconductors. Doping of groups 14 elements with group 13 elements (such as Indium) produces holes (electron deficiency) in the crystals. Thus, p-type semiconductors are produced. Then symbol 'p' indicates the flow of positive charge.
Paramagnetic (weakly magnetic): Such materials contain permanent magnetic dipoles due to the presence of atoms, ion or molecules with unpaired electrons.
Due to unpair electron of F-centers, solids containing F-centers (Farbe) are paramagnetic.

We know that resistance of a conductor is directly proportional to the temperature. So, when it is cooled below a certain temperature called critical temperature, the resistance tends to drop to zero and superconductivity can be observed.

Around $1993$, the highest temperature superconducting material was known. It has been a ceramic material consisting of $Hg, Ba, Ca, Cu$ and $O$ i.e, the compound was $HgBa _2Ca _2Cu _3O _2$

Intrinsic (pure) semiconductors are undoped semiconductors. The charge carriers i.e electrons and holes in this kind of semiconductor are equal in number. The electrical conductivity of these type of semiconductors is due to electron excitation.

Eg: $Si, \ Ge, \ etc…$