Analysis of optical band-gap shift in impurity doped ZnO thin films by using nonparabolic conduction band parameters

► Optical band-gaps of polycrystalline ZnO thin films were analyzed. ► Experimental carrier concentration range covered from 1016 to 1021 cm− 3. ► Nonparabolic conduction band parameters were used in theoretical analysis. ► The band-filling and the band-gap renormalization effects were considered. ► The measured optical band-gap shifts corresponded well with the calculated ones.