镧掺杂BaSnO_3薄膜的电学和光学特性

Electrical and optical behaviors of La-doped BaSnO_3 thin film

利用射频磁控溅射法在(LaAlO_3)_(0.3)(SrAl_(0.5)Ta_(o.5)O_3)_(0.7)(001)单晶基底上生长了镧掺杂BaSnO_3外延薄膜.通过Hall效应和热电势测量证实了镧掺杂BaSnO_3薄膜具有n型简并半导体特征,并且基于载流子浓度和Seebeck系数计算出电子的有效质量为0.31m_0(m_0为自由电子质量).镧掺杂BaSnO_3薄膜在可见波段具有良好的透明性(透过率大于73%).基于介电模型对薄膜的透过率曲线进行拟合,从拟合结果中不仅得到了薄膜的厚度为781.2 nm,能带宽度为3.43 eV、带尾宽度为0.27 eV和复光学介电常数随波长的变化规律,而且也强力地支持了基于电学参数计算电子有效质量的正确性.

La-doped BaSnO_3 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 BaSnO_3 is a critical factor and should be determined.In this work,the performances of epitaxial La-doped BaSnO_3 thin films grown on（LaAlO_3）_（0.3）（SrAl_（0.5）Ta_（0.5）O_3）_（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 BaSnO_3 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 ×10^（20） cm^（-3）,24.49 cm^2·V^（-1）·s^（-1） and 45.71 μV/K,respectively.The electron effective mass ~ 0.31m_0（m_0,the free electron mass） is extracted by combining the Seebeck coefficient and carrier density.Ba_（0.99）La_（0.01）SnO_3（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.