Structural, electrical, optical, thermoelectrical and photoconductivity properties of the SnO₂–Al₂O₃binary transparent conducting films deposited by the spray pyrolysis method

Abstract

In this paper, the SnO2–Al2O3 binary thin-film system has been deposited on a glass substrate by the spray pyrolysis technique. The effect of aluminum concentration on the structural, electrical, thermoelectrical, optical and photoconductivity properties of films was studied. The [Al]/[Sn] atomic ratio was in the range 0–100 at.% in solution. X-ray diffraction analysis shows that all films with different doping levels have polycrystalline SnO2 cassiterite phase. At doping levels of 40 at.% and above, the Al2O3 phase was observed and the sheet resistance of the films increased with increasing Al doping in the ranges from 5 at.% to less than 40 at.% and more than 60 at.% due to the substitution of Al3+ with Sn4+. Minimum sheet resistance of films was found in the range 40–60 at.%. Using Hall effect measurements, the majority carriers concentration obtained was of the order of 1018 cm−3. Hall effect and thermoelectrical measurements show that at doping levels between 10 and 20% and also higher than 60 at.%, majority carriers change from electrons (n-type conduction) to holes (p-type conduction). Also, a higher Seebeck coefficient value equal to -341 μV K−1 was obtained for the 30 at.% Al-doping level. The average transmittance of the films at low doping levels was about 75–90%. The photoconductivity properties of SnO2–Al2O3 thin films increased with increasing doping level.