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 (TA) 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.