دراسة نظرية لخواص التركيب الإلكتروني لطبقة نانوية من ‏اوكسيد الزنك المشوبة

Theoretical investigation of electronic structure ‎properties of doped zinc oxide nanosheet

The thesis describes the structural and electronic properties of the ZnO nanosheet doped with B, C, N, Al, Si and P has been investigated by performing density functional theory calculations. The aim of this study is to identify the effects of substituting from one to six atoms of oxygen with different impurities in super cell of the ZnO nanosheet composed of 84 host atoms by taking into account the impurities sites and its effects on the structural and electronic properties of ZnONSs using SIESTA program. The electronic properties can be controlled certainly a most significant step in the development of electronic devices by doping. All systems under consideration have been fully optimized.  bond length, and bond angle, binding energy/dopant atom, total and projected density of state, the total energy, electronic states, energy gap, some electronic variables (vertical ionization potential (VIP), vertical electron affinity (VAE), electronegativity (EN) and hardness (H)) have been calculated and compared with each other. The results show that B and P atom substitution expands the bond length with respect to pristine ZnONSs. Therefore, this density functional investigation shows that the high stability of ZnO nanosheet can be achieved for both dopants depending on the designed growth condition and type dopant. The configuration of B and Al atoms replacing O atoms is more stable than other doped. The HOMO and LUMO are slightly different and this suggests that according to the number, type and position dopant in structure play significant roles on electronic properties and improving the electron accepting ability. It has been found that the energy gap of ZnO nanosheets decreases gradually along with (B, C, N, Al, Si and P) ions.  B₂ and C₂, N₃ and P₃, Al₄ and Si₄ occupying O sites as compound have energy gaps for conductor materials. These results are potentially useful for spintronic applications.  The results showed that, vertical ionization potential and vertical electron affinity for B and Al doping and has donor level at 3.3eV. On the other hand, for the N and P doped ZnO nanosheet has acceptor level at 4.0eV. The electronegativity increased for N and P doped and hardness decreased for B, C and Al doped that is shown more energetic favorable.