Study Of Electronic Structures And Optical Properties Of Doped ZnO

ZnO is a wide-gap (Eg= 3.37eV at 300K) II-VI Oxide semiconductor with low dielectric constant, big photoelectric coupling coefficient, high chemical stability, large exciton binding energy (60 meV), and excellent optical, electrical and piezoelectric properties. ZnO has proven to be applicable in many fields such as UV detectors, light-emitting diodes and semiconductor lasers, photodetectors, surface acoustic wave devices, and solar cells, etc. ZnO materials research has made great success, mainly in the preparation of experiments, functional design and the theoretical work of electronic structure.Recently, ZnO-based diluted magnetic semiconductor attracted great attention. In this thesis, the electronic structure and optical properties of ZnO and transition metals and N co-doped and C-doped ZnO have been investigated by using the first-principles ultra-soft pseudo-potential approach of the plane wave based upon the Density Functional Theory. The main work are presented as follows:(1) The band structure, density of state and optical properties have been calculated based on the ZnO supercell constituted by experimental parameters. The calculated results indicate that ZnO is a direct wide band gap semiconductor material, and the covalent and ionic bond coexistence compounds, electronic of Zn-3d-2p and O is a certain orbital hybrid. The calculated band gap revised by the "scissors" operator agrees with the experimental result. The changes of optical properties are qualitatively interpreted in combination with the theory of electronics transition between bands and calculated electronic structure.(2)We have calculated band structure, density of state, electrons density difference and optical properties of ZnO co-doped with transition metal (Mn, Fe, Co, and Cu) and N,and analysized the charge transfer between impurity ions and anions. The calculation indicates that co-doping of transition metal (Mn, Fe, Co, and Cu) and N is in more favor of p-type ZnO. The optical properties of ZnO co-doped with transition metal (Mn, Fe, Co) and N are similar to those of ZnO doped only by transition metal (Mn, Fe, Co), but rather different from those of pure ZnO.(3)Electronic structure and optical properties of ZnO doped with two different types carbon have been investigated. The calculated results show that there is significant difference in electronic structure between the cases of C substituting O and C substituting Zn in ZnO, which is caused by both the electronic structure of C atom and its interaction with the neighbor atoms. It was furthermore found that the optical properties of ZnO are varied in the low-energy region after doping; while in the high-energy region, the optical properties are almost not influenced by doping with C. The above changes of optical properties are qualitatively interpreted in combination with the calculated electronic structure.