Ab-initio study of electronic, magnetic, and optical properties of Ni mono-doped and (I, Ni) co-doped CdS nanowires

Diluted magnetic semiconductors typically display induced ferromagnetism and spin-dependent interactions at high Curie temperatures, which is advantageous for application in magneto-electronic devices. The causes of ferromagnetism and optical emission dynamics, which have complex microstructural and compositional properties, are still not fully understood. Here, using first-principles calculations, the impact of Ni(II) ion substitution on the electronic, optical, and magnetic properties of CdS NW has been studied for the first time. The results show that when the size of the nanowire increases, the bandgap and binding energy decrease. The most favorable site for Ni doping was found to be at the surface of the nanowire. The most stable configuration with Ni ions on the surface of the nanowire has AFM as its ground state, which may be described using the super-exchange mechanism. The ground state configuration shifts from AFM to FM due to the addition of the extra electron provided by iodine (I) co-doping, and the estimated Curie temperature is expected to be higher than the ambient temperature. The fundamental bandgap of CdS nanowire is redshifted with Ni(II) doping, and the observed d-d intra-band transition in the absorption spectra at the low energy side of the optical bandgap is well consistent with the experimental results. Furthermore, the optical bandgap and d-d intra-band transitions in the optical absorption spectra are correlated with the magnetic coupling between Ni(II) ions, and we find a red-shift/blue-shift of d-d intra-band transition peaks and bandgap in the FM/AFM coupled ions system, supporting the experimental observations. The enhanced optoelectronic and magnetic properties of (Ni, I) co-doped CdS nanowires suggest their possible application in spintronic and optoelectronic devices, such as remote sensing and photovoltaics.