Since the estimation of band gap is usually carried out using the Tauc plots (Kubelka Munk function), how do you decide when to adopt a direct band gap or indirect bang gap approach?
Dear Panesun Tukur
The valence band and the conduction band can examine that which material has a direct band gap or has an indirect band gap. you should have a closer look to the bands. The minimum state in the conduction band and the maximum state in the valence band are each characterized by a certain crystal momentum (k-vector) in the Brillouin zone. If these k-vectors are different, the material has an indirect gap. If the crystal momentum of electrons and holes is the same in both the conduction band and the valence band, It has direct band gap. In an indirect band gap, a photon is not able to pass through a direct path, because the electron must pass through an interface state and transfer momentum to the crystal lattice.
On the other hand, the absorption coefficient is related to the energy of the photon, so we have this equations:
absorption coefficient = B/(hv)*(hv-Eg)^n
n is the power factor of the transition, B is the tailing parameter and Eg is the E band gap. The plot of the absorption coefficient versus hv can represent you the type of the band gap.
To get the idea on direct and indirect bandgap calculation, you can follow this article...
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You can use DRS then analysis with tuac plot. But i have a question: how can know the complex has direct or indirect band gap?
And
How does impurity bandgap affect complex bandgap?
If the bandgap of the impurity is small, will it reduce the bandgap of the final complex?
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