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Ivan Ohlídal, Daniel Franta, David Nečas

Ellipsometric and reflectometric characterization of thin films exhibiting thickness non-uniformity and boundary roughness

Applied Surface Science 421 (2017) 687-696

In this paper epitaxial ZnSe thin films prepared by molecular beam epitaxy onto GaAs single crystal substrates exhibiting two defects, i.e. boundary roughness and thickness non-uniformity, are optically characterized using a combination of spectroscopic ellipsometry and near-normal spectroscopic reflectometry. The influence of boundary roughness is included into optical quantity formulae by the combination of the scalar diffraction theory and Rayleigh-Rice theory. Thickness non-uniformity is incorporated by means of averaging the elements of the unnormalized Mueller matrices. The universal dispersion model of the optical constants of the ZnSe thin films based on parametrization of the joint density of electronic states is used. Very thin overalyers modeled by rough thin films with identically rough boundaries are taken into account on the upper boundaries of the ZnSe thin films. The spectral dependencies of the optical constants of the ZnSe thin films are determined within the wide spectral region (0.6–8.7 eV). Moreover, the mean thickness of the ZnSe thin films and thickness of overlayers are determined together with the other structural parameters characterizing the defects. The values of roughness parameters, determined by the optical method, are verified by a comparison with results achieved by atomic force microscopy. It is also shown that approximations of the local reflection coefficients presented are usable for processing the experimental data.

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DOI: 10.1016/j.apsusc.2016.10.186

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