Department of Materials Science and Engineering, Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104, USA.
J Phys Condens Matter. 2014 Dec 17;26(50):505502. doi: 10.1088/0953-8984/26/50/505502. Epub 2014 Nov 19.
The optical absorption properties of LaFeO(3) (LFO) have been calculated using density functional theory and experimentally measured from several high quality epitaxial films using variable angle spectroscopic ellipsometry. We have analyzed the calculated absorption spectrum using different Tauc models and find the model based on a direct-forbidden transition gives the best agreement with the ab initio band gap energies and band dispersions. We have applied this model to the experimental data and determine the band gap of epitaxial LFO to be ∼2.34 eV, with a slight dependence on strain state. This approach has also been used to analyze the higher indirect transition at ∼3.4 eV. Temperature dependent ellipsometry measurements further confirm our theoretical analysis of the nature of the transitions. This works helps to provide a general approach for accurate determination of band gaps and transition energies in complex oxide materials.
采用密度泛函理论计算了 LaFeO3（LFO）的光学吸收特性，并使用变角光谱椭圆偏振法从几种高质量外延薄膜中进行了实验测量。我们使用不同的 Tauc 模型分析了计算出的吸收光谱，发现基于直接禁带跃迁的模型与从头算带隙能量和能带色散吻合得最好。我们将该模型应用于实验数据，确定外延 LFO 的带隙约为 2.34 eV，且略微依赖于应变状态。该方法还用于分析约 3.4 eV 的更高间接跃迁。温度相关的椭圆偏振测量进一步证实了我们对跃迁性质的理论分析。这项工作有助于为复杂氧化物材料中带隙和跃迁能量的精确确定提供一种通用方法。
