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Band structure in solids
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The best way to understand a semiconductor is to consider the band structure of the material.

The conduction and valence bands are separated by a forbidden gap called the 'band gap', the size of which determines whether the material is classified as:

The interaction of a gamma-ray with semiconductor material can produce primary electrons with energies considerably larger than thermal energies. These interactions can raise electrons from deep occupied bands into energy levels well above the base of the conduction band. The resulting deeply embedded holes and the excited electrons will tend to redistribute themselves among the available energy levels until:

  • the electrons lie at the bottom of the conduction band; and 
  • the holes lie at the top of the valence band.

Have a go The simulation illustrates the three types of material and the direction of travel of electrons and holes in these materials.

It is important to understand that the mobility of electrons and holes both contribute to conductivity, for further explanation see here... 


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