Electrical and optical behaviors of La-doped BaSnO3 thin film

Abstract

La-doped BaSnO3 is regarded as a very essential material to construct transparent perovskite devices due to its super high electrical mobility in perovskite transparent conducting oxides. For understanding the high electrical mobility, the effective mass of the carrier in La-doped BaSnO3 is a critical factor and should be determined. In this work, the performances of epitaxial La-doped BaSnO3 thin films grown on (LaAlO3)0.3 (SrAl0.5Ta0.5O3)0.7 (001) substrate by radio-frequency (RF) magnetron sputtering technique are investigated. The electrical properties (resistivity, carrier density, mobility and Seebeck coefficient) and the optical transmittance are analyzed. In addition, it is proved from both the Hall effect and thermoelectric power measurements that the La-doped BaSnO3 thin films are n-type degenerate semiconductor. At 300 K, the resistivity, carrier density, mobility and Seebeck coefficient are 0.987 mΩ·cm, 2.584×1020 cm-3, 24.49 cm2·V-1·s-1 and 45.71 μV/K, respectively. The electron effective mass ～ 0.31m0 (m0, the free electron mass) is extracted by combining the Seebeck coefficient and carrier density. Ba0.99La0.01SnO3 (BLSO) thin film exhibits a high optical transmittance of 73% in the visible spectral region. In order to derive the band-gap energy, the complex dielectric constant, and the film thickness, the transmittance spectrum is simulated based on the dielectric model comprising the band-gap transition (O'Leary-Johnson-Lim model) and free electron excitation (Drude-Lorentz model). The band-gap energy, exponential band tail and thickness of the BLSO thin film are 3.43 eV, 0.27 eV and 781.2 nm, respectively. Wavelength-dependence of complex dielectric function of the BLSO thin film is also obtained from the fitted line. Additionally, the parameters (optical carrier density and mobility) resulting from the optical measurement are in agreement with the results from the electrical measurement, which supports the calculated electron effective mass aforementioned.