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.

No comments:

PlusTwo Physics

Ask Physics