Study Of Electronic Structures And Optical Properties Of Doped ZnO

ZnO is a wide-gap semiconductor material with energy gap 3.37eV at 300K, exciton binding energy about 60meV, and excellent ultraviolet light properties. ZnO has proven to be important in many fields such as blue or UV light-emitting diodes, lasers and photodevice, etc. On the other hand,transition-metal-doped ZnO can be a diluted magnetic semiconductor (DMSs) with Curie temperature above room temperature. ZnO-based DMSs can be widely used in Spin-FET, Spin-LED and so devices, which makes the device faster, smaller, power consumption lower, better stability. Due to its good optical and magnetic properties, ZnO-based DMSs is possibly applied to electronic information devices.In this thesis, Fe- and/or Ni-doped ZnO thin films on the glass substrates were prepared by sol-gel. We explored the optical properties and magnetic behavior of samples. The main work are presented as follows:(1)Band structure, density of state, optical absorption properties and dielectric function of ZnO doped with Fe or Ni and co-doped with Fe and Ni have been investigated by using density functional theory based on ultrasoft psuedopotential method. The calculated results show that a new peak appears at ~0.46eV in the imaginary part of dielectric function of doped ZnO. Moreover, the optical absorption spectrum shows an obvious red shift, and a strong peak is observed at 1.3eV after doping. The above results were qualitatively discussed in combination with the experimental and calculated results reported in the literature.(2)Fe and/or Ni doped ZnO thin films on the glass substrates were prepared by sol-gel spin-coating method. The morphology of these ZnO thin films observed by microscopy revealed that all the ZnO films are uniform and dense. The X-ray diffraction (XRD) results indicate all the ZnO films show preferential orientation along (002) direction and the grain size of ZnO films is ~13 nm. There are three emissions peaks are observed in the photoluminescence (PL) spectra at room temperature, which are located at 394nm, 420nm, and 480nm.The peak of ZnO thin films are not remarkably shifted after Fe and/or Ni doping, however, the intensity of the ultraviolet peak in doped ZnO thin films is significantly weakened, and that of blue emission is strengthened. The room-temperature ferromagnetism was observed for all the doped ZnO samples and it depends on the coupling between the current carrier caused by substituted ions and defects.