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High-entropy alloys (HEAs), which have been intensely studied due to theirexcellent mechanical properties, generally refer to alloys with multipleequimolar or nearly equimolar elements. According to this definition, Si-Ge-Snalloys with equal or comparable concentrations of the three Group IV elementsbelong to the category of HEAs. As a result, the equimolar elements of Si-Ge-Snalloys likely cause their atomic structures to exhibit the same core effects ofmetallic HEAs such as lattice distortion. Here we apply density functionaltheory (DFT) calculations to show that the SiGeSn HEA indeed exhibits a largelocal distortion effect. Unlike metallic HEAs, our Monte Carlo and DFTcalculations show that the SiGeSn HEA exhibits no chemical short-range orderdue to the similar electronegativity of the constituent elements, therebyincreasing the configurational entropy of the SiGeSn HEA. Hybrid densityfunctional calculations show that the SiGeSn HEA remains semiconducting with aband gap of 0.38 eV, promising for economical and compatible mid-infraredoptoelectronics applications. We then study the energetics of neutral singleSi, Ge, and Sn vacancies and (expectedly) find wide distributions of vacancyformation energies, similar to those found in metallic HEAs. However, we alsofind anomalously small lower bounds (e.g., 0.04 eV for a Si vacancy) in theenergy distributions, which arise from the bond reformation near the vacancy.Such small vacancy formation energies and their associated bond reformationsretain the semiconducting behavior of the SiGeSn HEA, which may be a signaturefeature of a semiconducting HEA that differentiates from metallic HEAs.

Semiconducting SiGeSn High-Entropy Alloy: A Density Functional Theory Study