What is meant by conductivity of Semi conducting materialsengineering physics

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PH2161-ENGINEERING-PHYSICS--II--->View question


What is meant by conductivity of Semi conducting materials?engineering physics

engineering physics


By:milan-ransingh

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|prajwalamv

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conductivity of the semiconductor is moderate not very high and not very low. The typicality of semiconductor is that the valance electrons in the semiconductor are not free like metal instead they become trapped in the bond between two adjacent atoms. Germanium and Silicon are two very popularly used semiconductors. The crystal structure of both semiconductors consists a regular repetition of the three-dimensional unit.
Let us take the example of germanium where there are 32 orbiting electrons across the nucleus in each atom. Each atom in the germanium contributes four valence electrons to make the covalent bond with four adjacent germanium atoms in the crystal. So the atoms are tetravalent. The inert ionic core of the germanium acts as a positive charge of + 4 electronic charges. The valance electrons in germanium crystal serve to bind one atom to the next. Hence, it can be said that the valance electrons are tightly bounded with the atoms in the crystal. Because of that, although a germanium atom has four valence electrons in it germanium crystal as a whole is not an excellent conductor of electricity. At absolute zero temperatures a semiconductor crystal behaves just like an insulator as there are no free carriers of electricity available. However at room temperature (300oK), some of the covalent bonds in the crystal are broken due to available energy and this phenomenon makes the availability of free electrons in the crystal and hence conduction of semiconductor may be some extent possible at room temperature. The energy required to break the covalent bond is about 0.72 eV in germanium, and that is 1.1 eV in silicon at room temperature.

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