TYPES OF SEMICONDUCTRORS . . Intrinsic semiconductors A semiconductor in its pure form without any impurity is called an intrinsic semiconductor . Here, impurity means .
The energy of the orbiting electrons is measured in electron volts (eV). Note . . Classification of materials The classification of solids into insulators, metals, and semiconductors can be explained with the help of the energy band diagram.
i) Insulators The energy band structure of insulators is shown in Figure . (b). The valence band and the conduction band are separated by a large energy gap. The forbidden energy gap is approximately eV in insulators.
The gap is very large that electrons from valence band cannot move into conduction band even on the application of strong external electric field or the increase in temperature. Therefore, the electrical conduction is not possible as the free electrons are not available for conduction and hence these materials are called insulators. Its resistivity is in the range of – Ωm. ii) Conductors In condutors, the valence band and conduction band overlap as shown in Figure .
(c). Hence, electrons can move freely into the conduction band which results in a large number of free electrons available in the conduction band. Therefore, conduction becomes possible even at low temperatures. The application of electric field provides sufficient energy to the electrons to drift in a particular direction to constitute a current.
For condutors, the resistivity value lies between – Ωm and – Ωm. iii) Semiconductors In semiconductors, there exists a narrow forbidden energy gap E eV g < between the valence band and the conduction band - - - - - - - - Unit electronics and Communication electrons as shown in Figure . (b). The vacancies produced in the valence band are called holes.
As the holes are deficiency of electrons, they are treated to possess positive charges. Hence, electrons and holes are the two charge carriers in semiconductors. In intrinsic semiconductors, the number of electrons in the conduction band is equal to the number of holes in the valence band. The electrical conduction