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Semiconductor Electronics: Materials, Devices And Simple Circuits (Physics) Class-12

Classification of Metals, Conductors, and Semi-conductors
  • Metals − Possess very low resistivity (or high conductivity)
  • Semi-conductors − Possess resistivity or conductivity intermediate to metals and insulators
  • Insulators − Possess high resistivity (or low conductivity)
  • Semi-conductors are of two types:
    • Elemental semi-conductor − Example: Si and Ge
    • Compound semi-conductor − Example: CdS, GaAs, CdSe, InP, etc.
  • Energy band diagram of metals or conductors

    • Conduction band is partially filled and the valence band is partially empty or the conduction and valence balance overlap.
    • Due to overlap, electrons can easily move into the conduction band. This situation makes a large number of electrons available for electrical conduction.
    • When the valence band is partially empty, electrons from their lower levels can move to higher levels making conduction possible.
  • Energy band diagram for insulators

    • Large band gap Eg exists. (Eg > 3eV)
    • Since there are no electrons in the conduction band, no electrical conduction is possible.
    • The electron cannot be excited from the valence band to the conduction band by thermal excitation.
  • Energy band diagram for semi-conductors

    • Energy band gap Eg is small. (Eg < 3eV)
    • At room temperature, some electrons from valence band cross the energy gap and enter the conduction band.

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