Calculations On Electronic Structure Of Chalcogenide Semiconductor Material And Investigation Of Their Quantum-dots Composite Film Electroluminescence Devices

As an important semiconductor material, chalcogenide semiconductor material hasexcellent photoelectronic characteristics and is widely used in the display and lighting area. Inthis dissertation, we focus on two typical chalcogenide semiconductor materials, ZnS and PbS.First, we calculated the electronic structure and optical properties of zinc-blend structure ZnS,ZnS：Er and face-centered structure PbS and discussed their relevance, which provide areasonable theoretical basis for experimental research. Then, the quantum-dots basedelectroluminescence (EL) devices with quantum-dots emitting layer and polymer functionallayer were prepared and their EL mechanism were discussed.(1) The2×2×1supercell of pure ZnS and Er3+doped ZnS with concentration of6.25%and12.5%were calculated based on first principle theory. In these calculation, themonkhorst-pack grids was set to2×2×4and the electron wave function was expanded inplane waves with a cutoff energy of370eV. The results show that the band gap of Er3+dopedZnS was narrowed compared to undoped ZnS and their absorption spectra were also revealed.(2) Convergence test was carried out in different cutoff energy in the calculation offace-centered structure PbS, and450eV was chosen as the optimum value. The calculatedband gap for face-centered structure PbS is0.54eV. The absorption, reflectance and lossfunction spectra were also obtained.(3) Single, double ZnS:Er layers and PVK/ZnS:Er composite film devices werefabricated and its EL mechanism were focused. With low applied voltage, the electrons wereinjected into lower defects energy. By voltage increased, higher defects energy level in ZnSwere filled up and the blue-shift EL spectra were observed. Further increases in voltage madeEr3+transitioned from4F9/2state to ground state appear at650nm. The EL spectra of hybridPVK/ZnS：Er device showed the broad emission over visible range which is owed to theoverlap of PVK, ZnS and Er3+.(4) The comparison between single MEH-PPV layer, single MEH-PPV layer andMEH-PPV/PbS composite film devices were discussed. The electroluminescence ofMEH-PPV/PbS composite film devices which emitted from PbS layer was enhanced by thehole transfer material MEH-PPV.