Abstract
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, A, A, A, B, and B, which polarization properties are studied under four different excitation energies. We found that the polarization orientations of the A and A modes under specific excitation energy can be useful tools to determine the GeS crystallographic directions: armchair and zigzag.
Highlights
Two-dimensional (2D) layered van der Waals semiconductors, such as transition metal dichalcogenides (e.g., MoS2 and WSe2 ) and post-transition metal dichalcogenides (e.g., InSe), have appeared as a fascinating class of materials for exploring novel excitonic phenomena [1,2,3,4,5]
We found that the low-temperature (T = 5 K) optical band-gap absorption is governed by a single resonance related to the neutral exciton, while the corresponding emission is dominated by disorder/impurity- and/or phonon-assisted recombination processes
We found that the polarization orientations of the A2g and A4g modes under specific excitation energy can be used to distinguish between armchair and zigzag crystallographic directions in germanium sulfide (GeS) crystals
Summary
Two-dimensional (2D) layered van der Waals (vdW) semiconductors, such as transition metal dichalcogenides (e.g., MoS2 and WSe2 ) and post-transition metal dichalcogenides (e.g., InSe), have appeared as a fascinating class of materials for exploring novel excitonic phenomena [1,2,3,4,5] In terms of their crystal structures, these materials are characterized by a high in-plane symmetry. There is a group of materials with a low in-plane symmetry, which includes, e.g., black phosphorus (BP) [6,7,8], or Re-based dichalcogenides Among these anisotropic materials, a new group of emerging vdW semiconductors, i.e., group-IV monochalcogenides MX (where M = Ge, Sn, or Pb and X = S, Se, or Te), has attracted increasing attention due to their anisotropic optical properties. The family of MX materials exhibits high carrier mobility, larger for monolayers as compared to bulk [11], which can lead to potential applications in angle-resolved opto-electronics
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
