In solid state ,we have three different material metal,semiconductor,and insulator . The band energy of these materials depends on the gap between valence band and conduction band . We clearly can see from the picture that the band gap reduces from insulator to metal (overlap) which means metal does not need heat to be conductor while semiconductor needs.
4/1/11
Basic concept of Energy Bands
In solid state ,we have three different material metal,semiconductor,and insulator . The band energy of these materials depends on the gap between valence band and conduction band . We clearly can see from the picture that the band gap reduces from insulator to metal (overlap) which means metal does not need heat to be conductor while semiconductor needs.
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The relationship between the fermi level and the band structure for the different types of materials is really interesting. That is, if the 1st energy band contains unoccupied energy levels that are above the fermi level, then it will be easy (require a relatively small amount of energy) for electrons to be promoted and hence it is a good conductor.
ReplyDeleteAnd similarly for insulators; the fermi level lies between the two bands, and so the states in the lowest band will be completely occupied while none of those in the second band will be. Therefore, the energy needed to be given to an electron to move it into the next band is much greater than for a metal (or semi conductor) and so it is not a good conductor.
ReplyDeleteBy providing this picture the meaning of band gap became clear to me. for this,i found the band gap play an important role to determine the type of solid. As i see from the picture,if the band gap large it will be insulator but if there is no gap it will be conductor.
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