First interpretation of phonon spectra of quaternary solid solutions using fine structure far-IR reflectivity by synchrotron radiation

In this work, we present and discuss far-infrared (FIR) reflectivity spectra obtained using infrared synchrotron radiation in different ZnxCdyHg1−x−yTe (ZMCT) quaternary alloys. Reflectivity spectra were measured at the DAFNE-light facility of the INFN-LNF with samples placed under vacuum inside a BRUKER Equinox 55 interferometer. Samples were cooled in a helium cryostat in a temperature range from about 20 K to 300 K. The obtained spectra were standard Kramers–Kronig transformed to obtain the imaginary part of the dielectric functions, then unfolded into a set of Lorentzian oscillators. The fitting procedure yields a total of 21 lines in the ZnxCdyHg1−x−yTe reflection spectra of these quaternary alloys. Sixteen lines have been correlated to ternary spectral contributions of the different components: CdHgTe, ZnHgTe and CdZnTe (with a precision of ±1.5 cm−1). In the wave number range between 108 cm−1 and 190 cm−1 the oscillator frequencies have been attributed to the spectral lines of these quaternary alloys.