Research On Properties Of Nb-doped TiO₂ Conductive Thin Films As Plasmonic Materials

Transparent conductive Nb-doped titanium oxide(TNO) exhibit good conductivity and high optical transparency in the light of visible regime and it is compatible with the standard semi-conductor manufacturing process. It can be easily fabricated in thin film form and other varieties of nanostructures. The real part of permittivity of Nb-doped titanium oxide transparent conductive oxide(TCO) thin film could be less than zero in the near-infrared regime and the loss of the film is lower than traditional noble metal plasmonic materials.This kind of plasmonic material has excellent tunability,it has the great potential as the new low-loss plasmonic material to alternate to the common metals.This thesis is mainly focused on the fabrication of transparent conductive niobium doped titanium oxide thin films by pulsed laser deposition(PLD) technology and on the analyses of the structural and electrical properties of the thin films. The optical characters of the plasmonic material in the near-infrared region were also investigated. The main contents of the thesis are as follows:(1) We decided to use the PLD to deposit TNO films on the fused silica substrates on the basis of literature investigation and experimental condition. XRD characterization suggest that the obtained thin films were anatase polycrystalline films with(101)preferential orientation. The transmittance of the films in the visible region were measured by an UV-vis spectrophotometer. Appropriate elemental technical parameters had been determined according to the analyses of variation of the transmission.It demonstrated that the performance are great when the oxygen partial pressure is 0.9Pa,the laser energy density is 2J/cm3,the repetition frequency is 5Hz and the film is in-situ vacuum annealed under 400~600?.(2) The Hall effect testing instrument and four-probe platform were exploited to measure the electronic transport properties in the films under different annealing temperature. The carrier concentration and Hall mobility tend to increase initially and thendecrease as the temperature increases. The carrier concentrations in the films are 3-9×1020cm-3,but the resistivity is high.(3) The optical parameters of the TNO films were measured by an spectroscopic ellipsometer and the permittivity of films were retrieved from the data fitting combined with a Drude model or Drude-Lorentz model. The plasmonic properties of films in near-infrared region with different Nb doping concentration and annealing temperature were studied.It was found that the real part of permittivity is below zero only when the wavelength is longer than 1.55 and the imaginary part is a little higher. The further optimization of experimental parameters could enable TNO as a low loss plasmonic material at the telecommunication wavelength of 1.55 ?m.