Band-gap widening of CdO thin films

Abstract

CdO thin films were deposited on silica glass substrates by rf sputtering. The orientation of the crystal axis in the films was changed by varying the sputtering conditions. The (100)-oriented films were annealed under various conditions to change the carrier concentration. A blueshift of the optical absorption edge was observed as the carrier concentration increased, and band-gap widening was analyzed using the Burstein–Moss formula. We found that the intrinsic direct-band-gap Eg0 (Γ15–Γ1 gap) and the reduced effective mass mvc* are 2.22±0.01 eV and (0.274±0.013)m0, respectively, at room temperature. The results are discussed in relation to the band structure of CdO.