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C, Si and Ge have same lattice structure...

C, Si and Ge have same lattice structure. Why is C insulator while Si and Ge intrinsic semiconductors?

Text Solution

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Atoms require less energy to release electron from the orbit away from nucleus.
There are four electrons in the second orbit in `""_(6)C`, four electrons in third orbit of `""_(14)Si` and four electrons in the fourth orbit of `""_(32)Ge`.
Hence, energy required to take out an electron from these atom (ionisation energy) will be least for Ge, more than that for Si and highest for C or the resistivity of material depends on the energy difference between their conduction and valence band and for C this energy difference is 5.4 eV, for Si it is 1.1 eV and for Ge it is 0.7 eV.
Hence, number of free electrons for conduction in Ge and Si are significant but neligibly small for C so Ge and Si are semiconductor and C is insulator.
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Knowledge Check

  • C and Si both have same lattice structure, having 4 bonding electrons in each. However, C is insulator where as Si is intrinsic semiconductor. This is because, …….

    A
    in case of C the valence band is not completely filled at absolute zero temperature .
    B
    in case of C the conduction band is partly filled even at absolute zero temperature.
    C
    the four bonding electrons in the case of C lie in the second orbit, whereas in the case of Si they lie in the third.
    D
    the four bonding electrons in the case of C lie in the third orbit, whereas for Si they lie in the fourth orbit.

  • ……as a impurity, when added in Si or Ge P- type semiconductor is obtained.

    A
    Arsenic
    B
    Antimony
    C
    Phosphorus
    D
    Boron

  • …… as a impurity, when added in Si or Ge P - type semiconductor is obtained.

    A
    Arsenic
    B
    Antimony
    C
    Phosphorus
    D
    Boron

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