ВПЛИВ СИЛЬНОГО ЛЕҐУВАННЯ АТОМАМИ In, Ga ТА Al НА ЕЛЕКТРОННУ СТРУКТУРУ ZnO: РОЗРАХУНОК IЗ ПЕРШИХ ПРИНЦИПIВ

This study describes the electronic and optical properties of Ga-, Al-, In- doped ZnO with various concentrations of impurity, employing first principles calculations based on density functional theory (DFT) and GGA+U correction methods. The dependence of the electronic properties on the concentration of dopants has been studied using supercells of different sizes. The lattice constants and band gap of ZnO calculated in this study are in agreement with experimental values. Supercell density-functional calculations show that the conduction band of heavily doped ZnO is modified by the presence of group-III doping elements, which give rise to small gaps in specific points of the Brillouin zone, modifying the conduction band dispersion in the way predicted, in a much simpler approach, by the band-anticrossing model. The calculation of the electronic structure showed that after doping, impurity states appear near the Fermi level and these states are delocalized in the whole conduction band. Also we found that the position of the Fermi level of the doped sample was shifted to a higher energy level compared with the undoped material. The conduction band near the Fermi energy was a combination of hybridized Zn sp-orbitals and Al, In, Ga s-orbital. According to the results, the optical band gap of ZnO is broadened due to the increased concentration of dopant atoms. It is established that in order to describe the change in the optical band gap, when doping with different impurities, it is necessary to take into account the Burstein-Moss effect, the structural deformation due to strong doping, the hybridization of the electron orbitals of the impurity and zinc ions, and the effect of point defects. This study also reviewed the effects of point defects on the electronic properties of In-doped ZnO including different concentration of O vacancies and Zn vacancies. The calculation results are in good agreement with the existing experimental data and the study can provide a theoretical basis for future applications of Ga-, Al-, In-doped ZnO in optoelectronics. [ABSTRACT FROM AUTHOR]