Acoustic Phonons in Quasi-2D Van der Waals Semiconductors Probed by the Inelastic Light Scattering Spectroscopy

We investigated the acoustic and optical phonons in quasi-two-dimensional antiferromagnetic semiconductors of the transition metal phosphorus trisulfide family, MPS₃, with Mn, Fe, Co, Ni, and Cd as metal atoms. The Brillouin-Mandelstam and Raman light scattering spectroscopies were used to measure the acoustic and optical phonon frequencies close to the Brillouin zone center along the Γ-A high symmetry direction. We found a large variation, over ~28%, in the acoustic phonon group velocities in this type of material with similar crystal structures. The measured data indicate that the optical properties and the semiconductors' electronic band gap affect the acoustic phonon peaks' width. The acoustic phonon lifetime extracted for some of the materials was correlated with their thermal properties. The obtained results are important for understanding the layered van der Waals semiconductors and assessing their potential for future applications.