Preparation And Luminescent Properties Of Zno Thin Films

ZnO is a wide direct band gap semiconductor with band gap of3.37eV and exciton binding energy of 60 meV at room temperature. It hasthe same structure as GaN and become a new opto-electronic material forapplication in new optical devices as a promising substrate material forGaN.ZnO thin films with smooth surface and high crystal quality wereprepared by DC reactive magnetron sputtering. The effect of theparameters of. oxygen partial pressures, .sputtering powder, workingpressure, substrate temperature, annealing in nitrogen gas and doping onthe surface morphologies, microstructure and optical characteristics werestudied respectively. The luminescence mechanism was discussed as well.With the increase of the oxygen partial pressures, sputtering powerand substrate temperature, the crystal. quality are increaced, and thendecreaced. Increasing working pressure can decreace the crystal quality.The crystal quality and the thickness of the films are two importantimpacts upon the transparency, and every technology parameter has itsfeature. The surface morphologies, crystal quality and transparency areimproved obviously by annealing in nitrogen gas. Doped with magneticion Ni and Fe leads to the improvement of the surface morphologies andcrystal quality, red shift of absorption edge.In this paper, the luminescence property was studied mainly.Photoluminescence (PL) spectrum of ZnO thin films includes two. peaks,which are the ultraviolet peak of 400 nm and the blue peak of 466 nm.The ultraviolet peak is attribute to transitions between electrons inconduction band and valence band as the former studies. And its locationand intensity are affected great by deposition parameters, annealing anddoping. The intensity of the blue peak is affected by the above threefactors as well, but its location keeps the same. The mechanism of theblue photoluminescence was discussed. The transformations of theintrinsic defects of ZnO thin films were analyzed according toQuasi-chemical reaction equation, such as oxygen vacancy(V_o), zinc vacancy(V_zn), antisite oxygen(O_zn), antisite zinc(Zn_o), interstitialoxygen(O_i) and interstitial zinc(Zn_i). We get that the bluephotoluminescence may be attribute to V_o, Zn_i or Zn_o. The bluephotoluminescence peak of the doped ZnO was discussed further. Finallywe get that the blue photoluminescence peak may be attribute to Zn_i.