Study Of Preparation And Characterization Of Metal-doped Nickel Oxide Films

Nickel oxide(NiO)is an important p-type conductive semiconductor with a wide band gap.NiO has excellent chemical stability as well as electrical,optical and magnetic properties,which makes it an attractive material for a wide range of applications,such as anti-ferromagnetic materials,electrochromic display devices,functional chemical sensors,solar dell and p-type transparent conductive electrode,etc.In this thesis,undoped and metal-doped NiO thin films were prepared by magnetron sputtering.The structure,composition,morphology,electrical and op-tical characteristic of NiO films were studied by X-ray diffraction(XRD),energy-dispersive spectroscopy(EDX),atomic force microscope(AFM),scanning electron microscopy(SEM),four-point probe technique and ultraviolet visible near infrared spectrophotometer(UV-VIS-NIR),respectively.Firstly,undoped NiO thin films were deposited by radio frequency(RF)mag-netron.It can be found from the XRD patterns,NiO films exhibiting great crys-tallinity with(111)preferential growth orientation.Compared to bulk materials,the lattice constantt a' for the NiO films are increased,indicating that the unit cell is stretched along(111)direction,causing a tensile force in the NiO films.After annealing,the preferential growth orientation of NiO films is changed from(111)to(200),the crystallinity is enhanced and grain sizes are increased.The resistivity of the NiO films decreases with the decrease of crystallinity and the increase of oxygen content.The transparency decreases with increasing oxygen content and the band gap also decreases.It can be found from the EDX spectra,the optimal crystalline NiO films with(111)preferential growth orientation are oxygen-rich NiO with atom-ic percentages of 68.27%and 31.73%for O and Ni,respectively.It can be observed from the SEM and AFM images that the surface of NiO film is composed of uniform and compact small particles,and the root mean square roughness is only 0.84 nm.Secondly,Cu doped NiO(Cu:NiO),Cu-Mn doped NiO(Cu-Mn:NiO)and Cu-Co doped NiO(Cu-Co:NiO)films were prepared by radio frequency(RF)and direct current(DC)magnetron co-sputtering.XRD results show that when Cu-doping power is 20 W,there is only NiO(111)preferential growth orientation,indicating the perfect solubility of Cu into NiO host lattice.However,when Cu-doping power is increased to 30 W,the additional secondary peaks corresponding to CuO(002)diffraction peaks appear in the Cu:NiO films,indicating that excessive copper doping forms CuO phases.However,for the Cu-Mn:NiO and Cu-Co:NiO films,the CuO phase was formed only when the doping power is increased to 60 W.The resistivity of the metal doped thin film is obviously reduced,indicating the metal doping improves the conductivity of the NiO film.It can be observed from the SEM and AFM,with the increase of the doping power,both the grain sizes and the root mean square roughness of the NiO films are increased.The conductivity of the doped NiO films,and the resistivity of the doped NiO films decreases with the increase of the doping power and so the conductivity of the films depend on the doping power.The optical characteristics testing indicate that the visible light transmittance of the doped NiO films is decreased,and the transmittance and the band gap decrease with increasing doping power.