Introduction
- Metals, Semiconductors and Insulators
On the basis of electrical conductivity\[(\sigma )\]or resistivity \[(\rho =1/\sigma )\] the solids are classified as
(i) Metals - have low resistivity
\[\rho \tilde{\ }{{10}^{-2}}\,to\,{{10}^{-8}}\Omega m\],
\[\sigma \tilde{\ }{{10}^{2}}\,to\,{{10}^{8}}S{{m}^{-1}}\]
(ii) Semiconductors - have intermediate resistivity
\[\rho \tilde{\ }{{10}^{5}}\,to\,{{10}^{0}}\Omega {{m}^{{}}}\]
\[\sigma \tilde{\ }{{10}^{-5}}\,to\,{{10}^{0}}S{{m}^{-1}}\]
(iii) Insulators - have high resistivity
\[\rho \tilde{\ }{{10}^{8}}\Omega {{m}^{{}}}\]
\[\sigma \tilde{\ }{{10}^{-8}}S{{m}^{-1}}\]
i.e. the Semiconductors are the materials whose conductivity is more than insulators but less than conductors.
Intrinsic semiconductors or pure semiconductors in semiconductors forbidden energy gap Eg is more than metals or conductors and less than insulators. Silicon (Si) and Germanium (Ge) are the examples of pure semi-conductors.
In pure or intrinsic semiconductor,
\[{{n}_{e}}={{n}_{h}}={{n}_{i}}\] Where\[{{n}_{e}}=no\].of electrons: \[{{n}_{h}}=no\]. Of holes and\[{{n}_{i}}=no\]. Of intrinsic carrier concentration. Impurity like pentavalent (As, Sb, P) or
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