Optical phonons in the wurtzstanniteCu2ZnGeS4semiconductor: Polarized Raman spectroscopy and first-principle calculations

Abstract

The vibrational properties of the wurtzstannite ${\text{Cu}}_{2}$${\text{ZnGeS}}_{4}$ are studied experimentally by polarized Raman scattering in off-resonant and resonant conditions and theoretically by ab initio lattice dynamics calculations. Twenty-nine modes from 45 Raman active theoretically predicted have been experimentally detected and identified, including polar ${\text{A}}_{1}$(TO), ${\text{A}}_{1}$(LO), and ${\text{B}}_{1}$(TO+LO)/${\text{B}}_{2}$(TO+LO) and nonpolar ${\text{A}}_{2}$ symmetry phonon modes from measurements on (2 1 0) and (0 0 1) crystallographic planes of ${\text{Cu}}_{2}$${\text{ZnGeS}}_{4}$ single crystals. The lattice dynamics calculations provide a full picture of the zone center phonon spectrum and allow the assignment of experimentally observed lines to first- and second-order lattice vibrations. Using resonance Raman conditions, a strong enhancement of the ${\text{A}}_{1}$(LO) modes with the highest longitudinal-transversal spiting is observed.