Temperature dependence of the main optical constants of a-Si:H

The present study examines the influence of temperature on the interband optical absorption coefficient of hydrogenated amorphous silicon (a-Si:H) through comprehensive experimental characterization and in-depth theoretical modeling, providing valuable insights into the underlying absorption mechanisms. Optical absorption spectra were recorded over a wide temperature range, enabling the evolution of the absorption edge to be traced, as well as the features of interband transitions and their sensitivity to thermal influences to be identified. Particular attention is paid to the analysis of the exponential absorption tail (Urbach tail), which reflects the degree of structural disorder in the material. The experimental data were processed using modern approximation methods based on established optical absorption models, enabling the determination of key energy parameters, including the band gap and Urbach energy. The temperature dependence of the characteristic phonon energy in a-Si:H was estimated using the Bose–Einstein model and the empirical Varshni relation, which describe the influence of electron–phonon interactions on the band structure and optical properties of the material. It was shown that, with increasing temperature, a noticeable shift of the optical absorption edge to lower energies is observed, caused by enhanced thermal vibrations and an increase in the degree of disorder. A comparative analysis of the Bose–Einstein and Varshni models demonstrates good agreement with experimental data but reveals differences in the accuracy of their description of temperature-induced changes in the band gap.

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