Thin Films of the Spinel Cd1+xIn2-2xSnxO4 Transparent Conducting Oxide Solution

Thin films of a transparent conducting oxide solid solution Cd_1+xIn_2-2xSn_xO₄ (x = 0.15, 0.45, and 0.70) were deposited via rf magnetron sputtering. X-ray diffraction indicated the films consisted of a polycrystalline spinel phase. Atomic force microscopy measurements revealed a surface root mean square roughness between 1.3 and 6.0 nm. Optical absorption was 10% or less in the visible for x = 0.15, 0.45, and 0.70. Optical gaps averaged near 3.5, 3.70, and 3.65 eV for films annealed in Ar/CdS of compositions corresponding to x = 0.15, 0.45, and 0.70. Conductivity exceeded 2000 S/cm for x = 0.15 and 4000 S/cm for x = 0.45 and 0.70. Mobilities of 43, 50, and 56 cm²/V s were measured for films annealed in Ar/CdS of compositions corresponding to x = 0.15, 0.45, and 0.70, respectively. Composition data obtained via electron probe microanalysis indicate the films are becoming Cd deficient during the annealing process. This suggests an excess of In⁺³ and/or Sn⁺⁴ on Cd⁺² sites may play a role in carrier production in these films. The Cd volatilization may also inhibit crystallization and decrease mobility.