David Nečas, Ivan Ohlídal, Daniel Franta, Miloslav Ohlídal, Vladimír Čudek, Jiří Vodák
Measurement of thickness distribution, optical constants and roughness parameters of rough non-uniform ZnSe thin films
Applied Optics 53 (2014) 5606-5614
Epitaxial ZnSe thin films exhibiting two important defects, i.e.\ boundary roughness and thickness non-uniformity, prepared on GaAs substrates, are optically characterised using a combination of variable-angle spectroscopic ellipsometry, spectroscopic near-normal reflectometry and imaging spectroscopic reflectometry. The influence of boundary roughness is incorporated into optical quantity formulae by the Rayleigh--Rice theory. The thickness non-uniformity is included using averaging of the unnormalised Mueller matrices. The dispersion model of the optical constants of the ZnSe films is based on parametrisation of the joint density of electronic states. Very thin overlayers represented by identical thin films are taken into account on the upper boundaries of the ZnSe films. The standard optical techniques are used to determine the spectral dependencies of the optical constants of the ZnSe films together with the parameters of roughness and thickness non-uniformity. Imaging spectroscopic reflectometry is then used to find the maps of the local thickness and local rms value of the height irregularities. The values of roughness parameters determined using the standard techniques and imaging spectroscopic reflectometry are verified by a comparison with results obtained by atomic force microscopy.
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