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MHT-CET : Physics Entrance Exam

MHT - CET : Physics - Semi Conductors Know More

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  • Energy Bands: In an isolated single atom, there are single energy levels. When two atoms are brought near each other, each single energy level splits. In a solid, the closeness of atoms results in multiple splitting of energy levels. Now each energy level splits into a very large number of closely spaced energy levels. These energy levels form a band. Thus bands of energy levels, instead of single energy levels are formed in solids.
  • Valence Band: The band which is occupied by the valence electrons or a band having highest occupied band energy is known as valence band.
  • Conduction Band: The next higher permitted band, after the valence band, is known as conduction band. It is the lowest unfilled energy band.
  • Forbidden Band Gap: The region between the conduction band and the valence band is known as forbidden band gap.
  • In Insulators: In insulators the forbidden band gap is wide and electrons from valence band can not easily jump across the gap and go into conduction band.
  • In Conductors: In conductors the conduction band and the valence band overlap. Hence plenty of free electrons are available for conduction.
  • In Semiconductors: In semiconductors the forbidden band gap is small. At 0K the conduction band is empty and valence band is completely filled. But at higher temperatures, electrons acquire sufficient energy to jump from valence band to conduction band and leave a hole behind in the valence band. The electrons move in the conduction band and the holes move in the valence band when an electric field is applied across a semiconductor.

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