Structure And Optical Properties Of Ag-doped ZnO Film

Due to its wide band gap (3.37eV) and large exciton binding energy (60meV), ZnO is believed to be a potential material for the use in ultraviolet or visible optoelectronic devices, such as light emitting diodes, laser diodes, and ultraviolet detectors. However, from the device point of view, high internal quantum efficiency does not always warrant high external efficiency. A large amount of light is usually trapped inside the luminescent layer that results in a low external efficiency. Therefore how to effectively extract light out of the material has become a major issue in device design. Recently, surface plasmon has been used as a means to couple light out of the luminescent layer.In this paper, Ag doped ZnO films are fabricated by pulsed laser deposition (PLD) at2.9x1O-4Pa,1.2x10-2Pa,1.1Pa and9.9Pa, on sapphire (0001) substrates and ZnO buffer layers, respectively. X-Ray Diffraction (XRD),?-scan, Electron Probe Micro-Analyzer (EPMA), and transmission spectrum are used to analyze content and structure properties. Optcial properties are characterized by photoluminescence (PL) and excitation spectrum. The results are summatized as follow:1. Metal Ag and Ag2O are precipitated from the Ag-doped ZnO films fabricated on sapphire substrates, which is determined by the oxygen pressure. The content of Ag goes up with the increase of oxygen pressure, and Ag2O goes down with the decrease. The epitaxial relationship is ZnO (0001)//sapphire (0001) and ZnO [1010]//sapphire [1120]. There is also ZnO (0001)//sapphire (0001) and ZnO [1010]//sapphire [1010] in the films fabricated at9.9Pa. The epitaxial relationship between Ag and ZnO is Ag(111) or (111)//A1203(0001), Ag[211]//ZnO [1010]. The films embedded with Ag nano-particles are found to have the enhanced photoluminescence emission due to the resonance effects of surface plasomons. ZnO buffer layer can improve the structure properties of Ag doper ZnO films.2. Resonance Raman scattering is found in the excitation spectrums of Ag-doped and Cu-doped ZnO films. The Raman peaks exist at the incident light, the energy of which equals to the sum of band gap and n times LO energies. The mechanism of resonance Raman scattering with stimulated emission is given to explain the phenomenon appears in the excitation spectrums. The LO energy measured by excitation spectrum can measure that whether the impurities are doped into the ZnO films.