Calculation and experimental verification for Zn _1-xCd _xS ternary mixed crystals on electronic structures and optical properties

The electronic structures and optical properties of Zn _1-xCd _xS ternary mixed crystals have been investigated using the first-principle plane-wave pseudopotential method. Comparison of calculations with different Cd doping concentration, the band gap shows gradually decrease with Cd doping concentration increasing. This band-narrowing phenomenon is ascribed to the reduction of bottom of conduction band determined by low energy electrons of Zn4s orbit and the elevation of top of valence band which was formed by the electrons of S3p states. Also the sulfur vacancy level was calculated and showed a shift near to the Fermi level with an increased of Cd doping concentration. The dielectric function and absorption coefficient of Zn _1-xCd _xS are also studied. For the absorption coefficient calculation of Zn _1-xCd _xS, we found that absorption onset in UV-Vis spectrum shifts to low energy with x increase. Moreover, the XRD, fluorescence spectrum and experimental absorption spectra of Zn _1-xCd _xS prepared by chemical synthesis and annealing treatment are obtained. The results exhibit agreement with the calculations.