Anisotropic Optical and Vibrational Properties of GeS

The optical response of bulk germanium sulfide (GeS) is investigated systematically using different polarization-resolved experimental techniques, such as photoluminescence (PL), reflectance contrast (RC), and Raman scattering (RS). It is shown that while the low-temperature (T = 5 K) optical band-gap absorption is governed by a single resonance related to the neutral exciton, the corresponding emission is dominated by the disorder/impurity- and/or phonon-assisted recombination processes. Both the RC and PL spectra are found to be linearly polarized along the armchair direction. The measured RS spectra over a broad range from 5 to 300 K consist of six Raman peaks identified with the help of Density Functional Theory (DFT) calculations: A [Formula: see text] , A [Formula: see text] , A [Formula: see text] , A [Formula: see text] , B [Formula: see text] , and B [Formula: see text] , which polarization properties are studied under four different excitation energies. We found that the polarization orientations of the A [Formula: see text] and A [Formula: see text] modes under specific excitation energy can be useful tools to determine the GeS crystallographic directions: armchair and zigzag.