First-principles calculations for understanding high conductivity and optical transparency in In_xCd_1-xO films

We investigate In_xCd_1-xO materials, where x = 0.0, 0.031, 0.063 and 0.125, to understand their high electrical conductivity and optical transparency windows, using the full-potential linearized augmented plane wave (FLAPW) method. In addition, we employ the screened exchange LDA (sX-LDA) method to evaluate accurate band structures including band gap that is underestimated by the LDA calculations. The results show a dramatic Burstein-Moss shift of the absorption edge by the In doping, reflecting the small effective mass of the Cd 5s conduction band. The calculated direct band gaps, 2.36 eV for x = 0.0 and 3.17 eV for x = 0.063, show excellent agreement with experiment. The effective mass of the conduction band of CdO is calculated to be 0.24 m_e (in the △ direction), in good agreement with an experimental value of 0.27 m_e, explaining its high electrical conductivity. The hybridization between the Cd 5s and the In 5s states yields complex many-body effects in the conduction bands: a hybridization gap in the conduction bands and a band-gap narrowing which cancels the further Burstein-Moss shift for higher In doping.