Study On Electronic Structure And Magneto-optical Properties Of (V , Cu, Fe) Single-doped ZnO

Zn O is a new type II-VI compound semiconductor with direct wide band gap of 3.37 e V, and high exciton binding energy of 60 me V at room temperature. It has more merits such as non-toxic, no pollution, abundant raw, low cost, high thermal stability, and high chemical stability etc. Therefore, Zn O has vast applications in the production of solar cells, liquid crystal displays, gas sensors, UV laser diodes, transparent conductive films, and diluted magnetic semiconductors.The electronic structure and magneto optical properties of Zn O can be improved and perfected by doping transition metal, and the controversial issue of effect on absorption spectra of doped Zn O has been solved reasonably. We simulated the undoped and doped Zn O using the first principles with the GGA+U method. We also focused on the effect on electronic structure and magneto optical properties of transition elements(V, Cu, Fe) doped Zn O. In this paper, the main innovations are as follows:Firstly, we study the electronic structures, magnetic properties and absorption spectra of three supercells for Zn1-x Vx O(x=0, 0.0417 and 0.0625). Calculated results show that with the increasing of V doping concentration, the doping becomes easier, the magnetic moments increase, the covalent bond becomes stronger, the ionic bond becomes weaker, the total energy reduces, and the doped system becomes more stable. Meanwhile, with the doping of V atom, doped systems produce excess electrons, the interaction between charges enhances, the Burstein-Moss effect is more obvious, the absorption edge shifts to lower energy, the optical band gaps widen, and blue shift of absorption spectra enhances.Secondly, contradictory results between blue shift and red shift of experimental absorption spectra have been reported in different literatures. To solve this problem, this study investigates the electronic structure and absorption spectra of substitutional doping for Zn1-x Cux O(x=0, 0.0313 and 0.0625) supercells and substitutional doping for Zn32 Cu O32 supercell. By increasing the Cu substitutional doping concentration, the following results are obtained: increased magnetic properties, narrower band gaps, and a significant red shift in the absorption spectrum. These are in good agreement with the experimental results. The changes of band gap and absorption spectrum for interstitial doping and substitutional doping are opposite.Thirdly, we study the electronic structures and optical properties of Fe-doped Zn O. The optical band gaps and absorption spectra Zn1-x Fex O(x=0, 0.0313 and 0.0417) have been calculated. By increasing the Fe doping concentration from 1.563 to 2.083at%, the following results are obtained: volumes increase, total and formation energies increase, doped systems become more unstable, the optical band gaps broaden and absorption spectra exhibit an obvious blueshift.Finally, given the unipolar structure of Zn O, four possible magnetic coupling configurations for Zn14Fe2O16 are calculated to study the magnetic properties. Results show that Fe doping can improve the ferromagnetism in Zn O system, and the ferromagnetic stabilization is mediated by the p-d exchange interaction between Fe-3d and O-2p orbital. Therefore, stable FM coupling and higher Curie temperature of DMS is likely to be a real effect.