Growth and Characterization of Radio Frequency Magnetron Sputter-Deposited Zinc Stannate, Zn2SnO4, Thin Films

Single-phase, spinel zinc stannate (Zn ₂SnO ₄) thin films were grown by rf magnetron sputtering onto glass substrates. Uniaxially oriented films with resistivities of 10 ^-2-10 ^-3cm, mobilities of 16-26 cm ²/Vs, n-type carrier concentrations in the low 10 ¹⁹cm ^-3 range were achieved. X-ray diffraction peak intensity studies established the films to be in the inverse spinel configuration. ¹¹⁹Sn Mössbauer studies identified two octahedral Sn sites, each with a unique quadrupole splitting, but with a common isomer shift consistent with Sn ⁺⁴. A pronounced Burstein-Moss shift moved the optical band gap from 3.35 to as high as 3.89 eV. Density-of-states effective mass, relaxation time, mobility, Fermi energy level, a scattering parameter were calculated from resistivity, Hall, Seebeck, Nernst coefficient transport data. Effective-mass values increased with carrier concentration from 0.16 to 0.26 m _e as the Fermi energy increased from 0.2 to 0.9 eV above the conduction-band minimum. A bottom-of-the-band effective-mass value of 0.15 m _e is in good agreement with local density approximation calculations. Temperature-dependent transport measurements and calculated scattering parameters correlated well with ionized impurity scattering with screening by free electrons for highly degenerate films.