Effect of atomic mass and isotopic disorder on the phonon spectra of isotope-enriched germanium crystals

Studied the influence of average atomic mass and isotopic disorder on the phonon spectra of lattice IR absorption and Raman scattering (RS) for single crystals of germanium isotopes $^{72}$Ge, $^{74}$Ge and $^{73}$Ge in comparison with $^{72}$Ge$_{0.5}$ $^{74}$Ge$_{0.5}$. At a temperature of 15 K, differences in the width and position of the two-phonon absorption bands in the IR spectra were observed for the monocrystalline germanium $^{72}$Ge$_{0.5}$ $^{74}$Ge$_{0.5}$ and $^{73}$Ge. In the first- and second-order RS spectra, a shift of phonon frequencies to the higher frequency region was found, associated with a decrease in the average atomic mass of germanium single crystals.