By accurate calculations of the experimental data of the absorption coefficient, It was found that the obtained optical energy gap of chalcogenide amorphous compositions be produced as a result of direct allowed transition. Is this possible?
I think that, most of semiconductors based on metal chalcogenides are direct band gap semiconductors
Amorphous materials often have a direct or quasi-direct gap. Basically, because states are localised in space, they are delocalised in k-space, so you don't need a phonon to match the momentum of the excited and ground states. Generally, if you want more information on chalcogenide glasses, I recommend the book my Mott & Davis.
Dear Dr. Manuel Schnabel
Dear Dr. Amr
Thanks for your answer and your contributions.
For amorphous materials, indirect transitions are valid according to Tauc relation
(αhυ)^(1/n)= β(hυ-Eg) so n = 2
But In the same time most of chalcogenide materials have direct allowed transition is the most probables case.
I calculated it by all possibilities, and I got that it may be direct for some samples and indirect for others.
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