Effect of annealing atmosphere and temperature on the properties of Cd2SnO4 thin films

Cadmium stannate (Cd₂SnO₄, CTO) thin films were prepared by radio frequency (RF) magnetron sputtering deposition followed by annealing at 550~650°C in Ar, air, Ar/4% H₂ and Ar/CdS at atmospheric pressure. The crystallization onset of the amorphous as-deposited CTO thin films occurs at 550°C, with highly crystallized single phase Cd₂SnO₄ obtained at 600°C and above. Electron mobility increases with the annealing temperature (T_A) and reaches mobilities of ~70, ~69 and ~56 cm²V^-1s^-1 for samples annealed at 650°C in air, Ar and Ar/CdS respectively. Although the samples annealed in Ar/CdS shows relatively lower mobility, the high carrier density ~6.6×1020 cm^-3 (annealed at 650°C) leads to a very low resistivity ~1.7×10^-4 Ω cm and a high optical bandgap ~3.6 eV due to Moss-Burstein shift. The resistivity of the samples annealed in air or Ar is limited by much lower carrier density.