Electrical and optical properties of wide-gap n-type Sn2Ta2O7 films

Abstract

Wide-gap n-type Sn2Ta2O7 polycrystalline films were prepared by RF-magnetron sputtering followed by annealing in a reducing atmosphere (N2). Sn2Ta2O7 is known to show both p- and n-type conductivity. The electrical and optical properties of the films were examined as a function of annealing time. The bandgap of the film was estimated to be 2.7 or 3.2 eV assuming an indirect or direct transition, respectively. The electrical conductivity of the film at 300 K increased from 2.1 × 10−8 S cm−1 (as-deposited) to a maximum of 2.1 S cm−1 (annealed for 14 h). The temperature dependence of the conductivity changed from semiconducting to degenerate semiconducting behavior with increasing annealing time, suggesting that oxygen vacancies were generated by the annealing in N2. From the temperature dependence of the mobility, it was found that neutral impurities were the dominant scattering centers for electron carriers.