Surface Evolution Of FTO Thin Films In The Process Of Annealing And Investigation Of Properites

The influences of annealed temperature on the structure, appearance, composition, photoelectric properties and microstress of FTO (fluorine doped tin oxide, FTO) thin film were investigated in this paper. The samples of FTO thin films with 4 mm substrate thickness were annealed from 20 to 700℃in the air. The structure and appearance of the film were studied by X-ray diffraction (XRD), Microscopes Raman Spectrometer, Field emission scanning electronic microscopy (FESEM), and Atomic force microscope (AFM). The photoelectric properties and microstress were analyzed by UV-vis spectrophotometer, Fourier infrared / Raman spectrometer, Physical Property Measurement System (PPMS) and XRD.The results indicate that the main components of the thin films are SnO2 and the crystal structure of which is rutile type. With the increase of the annealed temperature, the grain size increases constantly, the thin films has a preferred (211) orientation and the average grain size is 24.60 nm. The surface of films becomes smooth, the grains get closely-arranged and crystallinity of which get perfect gradually. After annealed at 400℃, the surface roughness reaches to the minimum value 13.71 nm. The hall coefficient, the sheet resistance (Rs) and resistivity of the thin films increase form 2.344×10^-4·cm, 9.377 /â–¡, 2.679×102 m³/C to 21.671×10^-4·cm, 86.683 /â–¡, 8.751×10² m³/C. Meanwhile, the carriers concentration decreases from 2.333×1016 cm^-3 to 0.714×1016 cm^-3.The curve of transmittance of the thin films shows a parabolic tendency in visible range, the transmittance of the sample annealed at 400℃reaches to the maximum value 87 % in the 500-600 nm range, with the increase of the annealed temperature, the transmittance T decreases constantly, which decreases to 68 % at 700℃. The curve of reflectance of the thin films shows a wave of osvillation tendency, with the increase of the annealed temperature, the reflectance R moves to long wave range and reaches to the maximum value 16 % at 600℃. In the far-infrared wavelength, infrared reflectance overall continuously decreased.The residual compressive stress exists in the thin films, with the increase of the annealed temperature, the values of compressive press show a trend of first decrease and then increase.