Mid-infrared complex permittivity in Bi2-xSbxTe3-ySey thin films synthesized using a combinatorial method

Successful employment of plasmonics-inspired solutions in the mid-infrared frequency range would benefit a number of highly important technologies. As a plasmonic material beyond gold and silver, Bi-based chalcogenide semiconductor alloys exhibit a wide tunability in the spectral dispersion of relative permittivity by varying the composition of their ternary and quaternary compounds. In our investigation, a combinatorial materials library of Bi2-xSbxTe3-ySey thin films were synthesized. The complete solid solubility and the in-depth chemical composition profile of thin film pixels in the library were confirmed using micro-area X-ray diffraction and secondary ion mass spectroscopy, respectively. The stoichiometries of thin film pixels were acquired using the energy dispersive X-ray analysis. The mid-infrared spectral transmittance was measured using a Fouriertransform infrared spectrometer. The complex permittivity epsilon(omega) in the spectral range from 2.5 to 15 mu m was derived by fitting spectral transmittance to the Drude-Lorentz equation. It can be demonstrated that the negative values of real part of permittivity, epsilon r, emerge at the shorter wavelengths. The crossover wavelength, at which epsilon r crosses zero from negative to positive, can shift from 5.346 mu m for Bi2Se3 to 9.232 mu m for Sb2Te3 with the increasing of x and the deceasing of y. Therefore, an exceptionally wide and potentially interesting mid-infrared plasmonic property, which is compositionally adjustable, can be carried out for evaporation-deposited Bi2-xSbxTe3-ySey solid-solution thin films.

Automated summary

The study reveals that Bi-based chalcogenide semiconductor alloys, through composition modulation, exhibit wide tunability in mid-infrared plasmonic properties. This research contributes to the development of highly important technologies.