Investigation On Optical And Electrical Properties Of Fluorine And Tungsten Co-doped Tin Oxide Low Emission Films

SnO₂-based films have great research significance in energy efficient glasses.By means of aerosol-assisted chemical vapor deposition?AACVD?experiments in combination with density functional theory?DFT?,we have investigated and characterized the optical and electrical properties of W-doped and W,F co-doped SnO₂ thin films?WTO and WFTO,respectively?.These two transparent conducting films were produced and deposited on soda-lime glass substrates by AACVD at 500°C with a mixture of butyltin trichloride?MBTC,as a Sn element sourse?and ammonium fluoride?NH₄F,as a F element sourse?or mixture of MBTC,NH₄F and tungsten hexachloride?WCl₆,as a W element sourse?,respectively.The composition preferred orientation,surface morphology,transmittance,electrical resistivity,carrier concentration,defect level and elemental state of the film were characterized and analyzed by XRD,SEM,Uv-vis spectrophotometer,Hall meter,photoluminescence,XPS and other testing methods.The main results are as follows:The first principles calculation results indicate that the doping of W and F atoms greatly improve the conductivity of the SnO₂ film.A fraction of Sn atoms can be replaced by W element when doped W to the original lattices of SnO₂ crystal structure,which changing the bonding strength of the valence electrons around the substitution site and improving the conductivity.The replacement of the O element in the original lattice structure by F atoms further changes the bonding strength of the valence electrons around the substitution site.The introduction of F and W atoms leads to the upward movement of the Fermi level and with increased conduction band filling,the Fermi level move above the conduction band minimum which resulting in the transitions of doping SnO₂ from the direct band gap to the indirect after doping,and exhibiting metallic properties.For WTO thin films,all the films of different W doping concentrations are tetragonal rutile structures and show a preferred orientation of?200?.Both the transmittance and the resistivity increase firstly and then decrease with the W-doping concentration increasesing.The optical and electrical properties are optimized at 2 at.%W-doping concentration.The average visible light transmittance,optical band gap value,minimum resistivity,carrier concentration and Hall mobility are 73.44%,4.03 eV,24.0×10^-4?·cm,2.608×10²⁰ cm^-3and 0.935 cm²·V^-1·s^-1,respectively.A large number of defects such as oxygen vacancies were observed which indicated that the doping elements have a significant effect on the formation and density of oxygen vacancy.The W,F co-doped SnO₂ thin films are also tetragonal rutile structures and have a preferred orientation of?200?.The W,F co-doped SnO₂ films are excellent in optical and electrical properties.The carrier concentration can reach about 14.71×10²⁰ cm^-3 at the doping concentrations of 2 at.%W and 30 at.%F,which is one order higher than that of the undoped SnO₂ film.Photoluminescence studies of WFTO have shown that the oxygen vacancies have a beneficial effect on luminescence property and conductivity.XPS results indicated that W and F enter the SnO₂ lattice and W elements are present in the lattice as W⁶⁺.