The Study On The Optical And Electrical Properties Of SnO₂: Sb Transparent Conductive Thin Films Deposited On Glass Substrates By R.F.Magnetron Sputtering

Due to high carrier concentration and wide optical band gap transparent conductive oxide thin films exhibit outstanding optical and electrical properties, such as low resistivity and high transmittance in the visible range etc. At present Sb-doped tin oxide (ATO) films show good electrical and optical properties and emerge as a potential alternative candidate for Sn-doped indium (ITO) films and it can be used as transparent electrode for optical and electrical device and low-e glass etc. Furthermore, they offer a number of advantages compared to the predominant ITO films nowadays: (i) cheapness; (ii) abundant raw materials; (iii) good stability. So the study on ATO film is becoming fashionable.In my experiment, ATO films were prepared by R.F. magnetron reactive sputtering in Argon and Oxygen atmosphere using a target mixed with Sb₂O₃ and SnO₂ and the films were figured by XRD, SEM, XPS, AFM, FT-IR, UV-Vis spectrosmeter, four-probe device and Hall effect system. It was concluded that the effect of process parameters had great influences on the structural, electrical and optical properties of ATO films. In addition the on-line vacuum annealing processing was studied.The results show that ATO exhibits tetragonal rutile structure. The antimony exits with two oxidation states (Sb³⁺ and Sb⁵⁺). The conductive mechanics consist of two facts, Oxygen hole in the crystal lattice of SnO₂ and the free electron applied by Sb⁵⁺ substitution for Sn⁴⁺. The optical and electrical properties of the films will be effect by two important processing facts during deposition: a) the crystallinity structure tends toward integrity; the thickness of the film decreases; the Hall mobility, carrier concentration and optical band gap width increase and the resistivity decrease with the substrate temperature increasing; the column structure of the pattern of the surface turns to brilliant orientations gradually with the rising of the substrate temperature; and the higher substrate temperature is benefit for optical and electrical properties of the ATO films; b) the content of the Sb⁵⁺ increases the Oxygen partial pressure during the deposition; the thickness of the films decreases, absorptionedge and threshold moves to blue region, and the optic-band gap increases with Oxygen partial pressure increasing during deposition. When there is no Oxygen during deposition, the film shows very large resistivity, while there is Oxygen in vacuum chamber, the films are all n type semiconductor. As for resistivity, carrier density and Hall mobility there is an optimum value with the increasing of the Oxygen partial pressure. In annealing experiments, the sodium ion of the substrate will diffuse into ATO film which has a bad affect on the optical and electrical properties of the films. The optical and electrical properties of the films will be improved by in-line vacuum annealing and SiO₂ isolate layer between substrate and ATO layer which can improve annealing temperature of the films and lengthen annealing time of the films. The optical and electrical properties of the films is as follow: the resistivity is as low as 2.51*10^-3ohm.cm, the carrier concentration is as high as 1.2*10²¹ cm^-3, the Hall mobility is 2.02cm²Â·m^-1.s^-1 and the transmittance in visible range is as high as 70% ,the reflectance in middle infrared range is 70%.