Abstract
Mn–Co–Ni–O thin films have important application values, but their spectroscopic ellipsometric properties undergoing post-annealing are still short of studies. In this Letter, the visible near-infrared ellipsometric data of post-annealed thin films were fitted by double Lorenz, Drude, and effective medium approximation models. We found that the Lorenz model can describe the small polaron oscillation, and the Drude model can excellently fit the conductivity produced by small polaron hopping. We found that a large number of carriers hopping between bound states under certain voltage generates a unidirectional flow of quasi-free carriers, which can bring about the same macroscopic properties as free carriers in extended state, and the calculated effective mass of quasi-free carriers is about ( is the effective mass of electrons). We also found that it is mainly Lorentz oscillators and the quasi-free carriers that produce the resonance absorption of electromagnetic waves in the visible near-infrared waveband, and both have electron absorption of lights. These results will perfect the small polaron hopping theory for Mn–Co–Ni–O thin films.
© 2017 Optical Society of America
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