Question

What is the difference between the direct bandgap and indirect bandgap? How do you measure the bandgap typically? (Please briefly description)

Answer 1

In semiconductor physics, the band gap of a semiconductor is either a direct band gap or an indirect band gap.

The minimum energy state in conduction band of semiconductor and the maximum energy state in the valence band of semiconductor are characterized by a certain momentum given by k-vector. For suppose the k-vectors are the identical, it is called a "direct gap".

If they are not , then it is an "indirect gap".

The band gap is known as "direct" if the momentum of both electrons and holes is the identical in both the conduction band and the valence band of semiconductor ; an electron can emit a photon directly.where as in an "indirect" gap, a photon cannot be emitted because the electron should pass through an intermediate state between and also transfer momentum to lattice.