Hadi Jabbar Alagealy thanks for your reply. Steffen Strehle i am working on the topological insulator Bi2Se3. How to calculate its bandgap while there is no saturation/ cutoff region in the absorption data. I mean if there is no cutoff/ saturation region then what does that means?
In my opinion, if there is no saturation/ cutoff region in the absorption data ,then it is also possible to establish the band gap using the slope concept in two different region of your plotted data.