After formation of a thin film, should the urbach energy value be always less than that of bandgap energy?

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Ramezan Sahebi

Urbach energy is the tailing of trap levels into the forbidden band gap, so it can not be greater than the value of Eg. It seems that you made a mistake in evaluating the Eu from Ln(a) vs. hu plots.

Chandra Bhal Singh

Read this article. It will solve your problem. The Urbach energy will always less than the bandgap of the material.

Omar M S

I recommend both answers from Sahebi and Singh

For more details you can read the book of

“optical processes in semiconductors” by Pankove