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First-principles study of optical properties in Ca-doped ZnO alloys

Various electronic and optical properties of Zn1−xCaxO ternary alloys of wurtzite structure are calculated using a first-principles approach based on the framework of the generalized gradient approximation to density-functional theory. In particular, on-site Coulomb interactions are introduced, which can reasonably well predict the electronic properties and band gaps of the Zn1−xCaxO (0≤x≤0.25) system. The imaginary part of the calculated dielectric function indicates that the optical transition between O 2p states in the valence band and Zn 4s states in the conduction band shifts to the high-energy range as the Ca concentration increases. The calculated band gap shows a significant increase with increasing Ca concentration. Therefore, Zn1−xCaxO ternary alloys may be a potential candidate alloy for optoelectronic materials, and especially for light-emitters and detectors.