The Electronic Structure And Optical Characteristics Of Magnesium Oxide Crystals

Magnesium oxide （MgO） has drawn world-wide interest due to its application in plasma display panel （PDP）, deep ultraviolet devices and quantum dots, and so on.In this thesis, we systematically investigate the electronic structure of Zn, Sc, Ca, and Sr doped MgO utilizing density functional theory andstate-of-the-artGW method. We further explore the exciton spectrum withthe Bethe-Salpeter equation （BSE）based on the electronic band structure corrected by the GW method. In addition, the secondary electron emission coefficientsof these materials are calculatedand their relationship with dopants and concentration are discussed consideringPDP as one application.We find that the band gap of MgO can be tuned effectively via doping.MgO doped with metal oxides, such as ZnO, CaO and SrO, has smaller band gap compared to pure MgO. The band gap of Mg^1-xA_xO decreases as the doping concentration increases.DopantScO, introduces mid-gap states and decreases the band gap. Moreover, the ternary compound has a ferro-magnetic ground state. The reduction of band gap and the introduction of mid-gap states are favorable for the performance of MgO protective layer in PDP. All these improvements in theelectronic structure increases the secondary electron emission coefficientγ, thus reduce the firing voltage and improve the discharge efficiency. Under external electric field, the conduction bands shift towards lower energies and the band gap are reduced, but the electric field in PDP is too weak to have impact on the intrinsic band gap pure MgO.Further analysis into the exciton spectrum reveals that the GW+BSE approach, which takes into account the electron-hole interaction, gives more accurate results compared to experiments. The exciton spectra of Mg^1-xA_xO are red-shifted as the doping concentration increases. For example, the first excitonic peak of Mg^1-xZn_xO shifts from 5.75 eV to 3.23 eV as x increases from 0 to 0.5. For Mg^1-xCa_xO, the first excitonic peak shifts from 5.75 eV to 4.82 eV as x increases from 0 to 0.25, while for Mg^1-xSr_xO the first peak shifts to 4.42 eV. Also, the magnitude of red-shift is closely related to the species of the dopant. For x=0.125, the first excitonic energy for Zn, Sr, and Ca doped MgO are located at 4.67 eV,4.82 eV and 5.12 eV, respectively. The exciton radius increases as thedoping concentration increases, while the exciton binding energy decreases. We also find that the simple hydrogen-like atom model provides a less computationally-demanding yet accurate enough approach to investigate the excitons of doped MgO.