Question

What is direct band gap and indirect band gap?

Answer 1

1.In direct bandgap semiconductor(DBS) the bottom of the conduction band and top of the valence band lie for the same value of k( where k=0). but in an indirect bandgap semiconductor(IBS) the bottom of the conduction band and top of the valence band lie for different values of k. where k is the electron crystal momentum.2. In DBS photon assisted transition occurs. Photons are massless entities and carry little momentum and this kind of transition is essentially vertical in the E-k diagram.In IBS, phononassisted transition occur which is horizontal in nature.The momentum of phonon is comparativelylarge.

Answer 2

Direct band gap and indirect band gap:

Direct Band Gap:

• The valence band present at the top and the conduction band present at the bottom lies at the same value of the momentum is recognised as a direct bandgap.

• In a direct bandgap, recombination release with the discharge of the energy.

• Here the radioactive recombination is high.

Indirect bandgap:

• The valence band at the top and the conduction band at the bottom level lies at the different values of momentum is defined as an indirect bandgap.

• In an indirect bandgap, due to a corresponding variation in momentum, it is conserved by the discharge of energy by only after both the momenta align themselves.

• Here the radioactive recombination is low.

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