Optical phonons and structure of TlGaS₂, TlGaSe₂, and TlInS₂ layer single crystals

The polarization properties of bands in Raman scattering and IR reflection spectra are studied experimentally in TlGaS 2 , TlGaSe 2 , and TlInS 2 layer single crystals and in solid solutions based on them. Additionally the angular dependence of IR‐active modes on the angle between the phonon wave vector and the direction of the optical axis c of single crystals is investigated. It is shown that the observed phonon spectra can be interpreted on the basis of a primitive cell which contains two tetragonal‐symmetry layers bonded to each other by an inversion operation. Bands corresponding to cells with a mixed composition are observed in the Raman spectra of the solid solutions.