Optical absorption spectra in the far-infrared range and phonons of CdSe1−xTex thin films

[Display omitted] •Far IR spectra of CdSe1−xTex films are measured using the synchrotron radiation.•DFT calculations of the lattice and molecular dynamics (MD) of the films are conducted.•Experimental infrared spectra of CdSe1-xTex films are analyzed using DFT calculations.•Redshift of the optical vibration mode of Cd108Te108 thin film is simulated using MD. Optical reflection spectra of CdSe1-xTex thin films deposited on quartz substrates are measured using the synchrotron radiation in the spectral range of 20–500 cm−1. The absorption bands of CdSe, CdTe, CdSe0.75Te0.25, CdSe0.5Te0.5, and CdSe0.25Te0.75 films are localized in the range of 20–220 cm−1. The imaginary parts of the dielectric function ε2(λ−1) of CdTe1-xSex crystals calculated in the framework of the density functional theory are in good agreement with the experimental reflection spectra of CdTe1-xSex films. The eigenvectors of the dynamical matrix CdTe1-xSex crystals are analyzed for several phonon modes to understand the difference between the frequency dependences of the calculated vibration density of states and the imaginary part of dielectric function ε2(λ−1). Small features of the experimental reflective spectra of CdSe1-xTex films in the ranges 50–70 cm−1 and 80–120 cm−1 are explained using the analysis of results of the molecular dynamics. During comparative molecular dynamics calculations, it was found that the vibration density of states of a thin CdTe slab with a surface-to-volume number of atoms relation of NS/NV = 0.2, experienced a redshift of approximately 30 cm−1. This shift was observed in comparison with the CdTe single crystal.