Opto-electronic properties of carbon doped NiO

Hybrid functional first principles calculations reveal the effects of substitutional carbon on electronic and optical properties in the anti-ferromagnetic configuration of NiO. Spin polarized projected density of states and unfolded band structures show electronic band edge modification and magnetic anisotropy due to carbon substituting both at nickel and oxygen sites; only carbon substituted at an oxygen site, however results in the emergence of inter-band gap impurity states. This is due in part to the steric differences between carbon substituting nickel vs oxygen as well as the difference in valence between carbon and oxygen. Carbon substituting nickel is more stable than substituting oxygen, with a lower formation energy both in O-rich and O-poor conditions. Charge density isosurface plots reveal that carbon substituting nickel does not result in any appreciable modification to the bonding profile around the substitution, while oxygen substitution results in the formation of covalent bonds between the carbon and the nearest nickel atoms. Substitutional carbon at either the nickel or oxygen site causes a red shift in all optical properties towards the visible light region. The anisotropy in the optical and electronic properties for both carbon substitution at nickel and oxygen sites implies that these properties may be tuned through carbon doping and oxygen growth control for transparent conducting oxide and optoelectronic device applications.