First Principles Study Of The Of Znse Electronic Structure And Nature

Because of their excellent photoelectric conversion and photo-electro-catalytic activity,Ⅱ-Ⅵsemiconductor light-emitting materials have been used as optical materials, solar energy materials, piezoelectric crystals, laser materials and other fields. And ZnSe is considered to be a better candidate for the preparation of blue-green laser material, which has been attracted many researchers'attention. At present, some theoretical and experimental investigations have been done on electronic structure,doping,conductivity model, defect states,surfaces and interface of ZnSe, but there are still some discrepancies, such as the route of the phase change under high pressure, the effects of impurity and defect on optical properties of ZnSe. Therefore using the first principles method, the electronic structures and optical properties for the different phases of ZnSe,the intrinsic Zn vacancies and doped with vanadium have been investigated with ultra-soft pseudo-potential approach of the plane wave based upon the Density Functional Theory (DFT). The main contents are as the following:1. The electronic structure and optical properties of zinc blended structure ZnSe under different pressures have been calculated. And the total energy, density of state, energy band structure, and optical absorption and refection properties have been discussed. Furthermore, the changes of electron structure, band structure and optical properties under high pressure have been analyzed in comparison with the experimental and theoretical data.2. Geometric structures, density of states and band structures of zinc blended structure and rock salt structure of ZnSe at different pressures (from 0 Gpa to 20 Gpa) have been calculated. Based on those results, the structure of the ZnSe phase transitions, elastic constants, bonding and phase transition under pressure have been discussed. From the principle of enthalpy for the ZB and RS ZnSe, the pressure at the phase transition is equal to 15.3 Gpa, which is greater than the results of 11.52 Gpa from the elastic constants of the phase transition criterion. And the change of phase to SC has not been found at the pressure of 9.5 Gpa; and the sp3 hybrid orbital have not been eliminated during the structure phase transition, while the 4s electronic state of Zn atom has a major contribution to the conductivity in RS phase.3. The geometric structure of V-doped and Zn vacancy for blended structure ZnSe have been optimized firstly, then the electronic structures and optical properties of the Zn vacancy in ZnSe with self-compensation effect and photo catalytic properties have been discussed. The results gives that, for V-doped ZnSe and Zn vacancy, there was no lattice distortion because of the existence of impurities; for V-doped ZnSe system, due to the existence of the impurity atomic energy level, the energies near Fermi level become continuous, and it shows the metal properties, while for the Zn vacancy the Fermi energy declines, and the conductivity and luminescence greatly increase. The dielectric peak is extended to the infrared area, so ZnSe containing Zn vacancy can be applied to the infrared optical catalytic experiments.