  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 low and room
($T$=300 K) temperature RS spectra consist of six Raman peaks identified with
the help of Density Fuctional Theory (DFT) calculations: A$^1_{\textrm{g}}$,
A$^2_{\textrm{g}}$, A$^3_{\textrm{g}}$, A$^4_{\textrm{g}}$,
B$^1_{\textrm{1g}}$, and B$^2_{\textrm{1g}}$, which polarization properties are
studied under four different excitation energies. We found that the
polarization orientations of the A$^2_{\textrm{g}}$ and A$^4_{\textrm{g}}$
modes under specific excitation energy can be useful tools to determine the GeS
crystallographic directions: armchair and zigzag.
