Anisotropic Optical And Vibrational Properties Of GeS

TL;DR

This study systematically investigates the anisotropic optical and vibrational properties of bulk GeS using polarization-resolved techniques, revealing polarization-dependent spectra and identifying vibrational modes with DFT calculations, aiding in crystallographic orientation determination.

Contribution

It provides a comprehensive polarization-resolved analysis of GeS optical and vibrational properties, including DFT-identified Raman modes and their polarization behaviors, enhancing understanding of GeS anisotropy.

Findings

RC and PL spectra are linearly polarized along the armchair direction.

Six Raman peaks are identified and their polarization properties studied.

Polarization orientations of specific Raman modes can determine crystallographic directions.

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 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.