Question

The parabolic approximation in conduction band and valance bond​

Answer 1

Answer:

(a) Conduction band

The conduction band is the band of electron orbitals that electrons can jump up into from the valence band when excited. When the electrons are in these orbitals, they have enough energy to move freely in the material. This movement of electrons creates an electric current.

(b) Valence band spectra

The valence band region of carbons shows some marked differences for different types of carbon. In the important early work of McFeely et al. (1974) an extensive study of carbon valence bands was conducted.

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Answer 2

Parabolic approximation of valence and conduction band:

• We found that in the presence of the bandgap the conceivable states in the valence band and the conduction band intersect only with the ends of the distribution.  

• For energies far away from the band edges the dispersal function drops off exponentially and those states are barely ever populated.  

• Thus, it can disregard the exact band structure and enlarge the energy dependence in the Taylor series of 2nd order in "k" around the valence band maximum (VBM) and the conduction band minimum (CBM), correspondingly. This is recognized as the parabolic band approximation.