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Parametric optical property database for CdSe1-xSx alloys
Maxwell M. Junda,Corey R. Grice,Yanfa Yan,Nikolas J. Podraza 대한금속·재료학회 2019 ELECTRONIC MATERIALS LETTERS Vol.15 No.4
A comprehensive database of the optical response in the form of complex dielectric function (ε) spectra of magnetron cosputteredCdSe1−xSx alloy thin films is developed spanning the full 0 ≤ x ≤ 1 range of compositions. A parametric modelis presented and used to determine ε describing each film while in both as-deposited and thermally annealed states. Thismodel combines a critical point electronic transition lineshape and an Urbach tail in the above- and below-bandgap portionsof the measured spectrum, respectively, while maintaining first derivative continuity. Additionally, this hybrid parametricdescription of ε automatically determines the Urbach energy (EU) describing the width of the sub-bandgap absorption tail,thereby providing a relative measure of the defect density of the modeled material. These as-deposited CdSe1−xSx films aregenerally found to be the most defective at intermediate compositions with some EU reaching energies > 200 meV. Annealingreduces EU in all films to a relatively uniform value < 100 meV for all compositions. Leveraging the full ε database inmodeling CdS-CdSe bi-layer stacks is demonstrated to be effective in detecting the composition gradients resulting frominter-diffusion upon annealing. The accuracy of this technique is verified through excellent agreement with cross sectionalenergy dispersive X-ray spectroscopy measurements.