Improved Tauc-Lorentz model: Impacts of roughness/additional oscillator(s) on determination of optical properties of HfO2 films

Abstract

Accurate determination of optical properties is crucial for optimal application of HfO2 film in optoelectronic industry. In this work, the effects of additional oscillator(s) introduced into Tauc-Lorentz model (the improved TL model) on the extracted optical properties of HfO2 film have been investigated with a roughness layer considered or not. The results show that the effect of additional oscillator(s) on optical properties depends on the electronic structure of HfO2 film, i.e., amorphous and/or polycrystalline character. The appearance of a shoulder-like absorption peak at ∽ 6 eV and a weak discrete absorption peak at ∽ 5.2 eV on the curve of dielectric function of the 350 nm polycrystalline HfO2 film confirms that additional oscillators correspond well with changes of the electronic structure probably induced by crystal field and defects. The results indicate that the improved TL model can be well applied to crystalline/polycrystalline films as well as defects near the absorption edge, and further probably to the fine electronic structure of materials, which greatly extends the application of TL model.