Microstructure And Properties Behavior Of Dual Acceptor Doner Doped ZnO Thin Films

The ZnO films doped with Ga-N and Ag-Ga-N were prepared by RF magnetron sputtering method. The surface morphology, phase structure, optical and electrical properties were systematically investigated by atomic mechanical microscope (AFM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), photolumicescence spectroscopy and Hall effect apparatus.It was found that the surface roughness of ZnO films doped with Ga-N and Ag-Ga-N increases when sputtering power, substrate temperature or annealing temperature increases,while decreases with the increase of pressure. In addition, it firstly increases and then decreases when the N₂ concentration changes from 0% to 80%. The increase of sputtering power, substrate temperature and annealing temperature enlarged the surface particles. Moreover, the size of the surface particles decreases firstly and then increases when the sputtering pressure and the N₂ concentration increase. O element mainly conbines with Zn to form Zn-O bond in the ZnO film although free O element also can be detected. N element combines with Ga or Zn to form Ga-N or Zn-N bonds in the doped ZnO films. In the Ag-Ga-N doped ZnO films, the amount of the free O decreases, while the amount of N element as N₂, (NH4)+, (NH2)- increases relatively.The results show that in the Ga-N doped ZnO thin films, the UV emission peak caused by the free excite recombination was at about 371nm, corresponding to the band gap Eg=3.34eV. The UV luminous intensity increases when the grain size of the ZnO films increases. In the purple band, it can be observed the luminescence caused by Ga-N donor-acceptor recombination. However, in the Ag-Ga-N doped ZnO films, the intensity of orange emission decrease, indicating that the formation of Oi is depressed due to the Ag-doping. The UV emission peak of the Ag-Ga-N doped films red-shift 2nm after annealing, suggesting that the band gap becomes narrow. When the annealing temperature is 620℃, the emission peak at 529 nm related to AgZn was detected. That means that the Ag atom can replace the Zn atom in ZnO films after the proper annealing treatment to form AgZn.The calculation results based on the PL spetrum obtained at 20K in multi-doped ZnO films show that the energy level of the acceptor No is 142meV and that of the donor GaZn is in a range of 94-124meV. The Ag-doping results in the obvious increase of the emission related to the neutral doner bound excition. This indicates that the Ag-doping induced the serious lattice distortion of ZnO film. As a result, more donor was introduced.The Ag-doping leads to the increase of the carrier concentration and the decrease of the Hall mobility in the Ag-Ga-N doped ZnO films. The Ag-Ga-N doped ZnO films with the depostion power of 80W, press of 2Pa and N₂ concentration of 40% shows the largest electron carrier concentration: n = 2.44 1019/cm3 and the smallest resistivity:ρ=0.213Ωcm after the films were annealed at 700℃for 1h.