In-Plane Optical Anisotropy of Layered Gallium Telluride

Abstract

Layered gallium telluride (GaTe) has attracted much attention recently, due to its extremely high photoresponsivity, short response time, and promising thermoelectric performance. Different from most commonly studied two-dimensional (2D) materials, GaTe has in-plane anisotropy and a low symmetry with the C2h(3) space group. Investigating the in-plane optical anisotropy, including the electron-photon and electron-phonon interactions of GaTe is essential in realizing its applications in optoelectronics and thermoelectrics. In this work, the anisotropic light-matter interactions in the low-symmetry material GaTe are studied using anisotropic optical extinction and Raman spectroscopies as probes. Our polarized optical extinction spectroscopy reveals the weak anisotropy in optical extinction spectra for visible light of multilayer GaTe. Polarized Raman spectroscopy proves to be sensitive to the crystalline orientation of GaTe, and shows the intricate dependences of Raman anisotropy on flake thickness, photon and phonon energies. Such intricate dependences can be explained by theoretical analyses employing first-principles calculations and group theory. These studies are a crucial step toward the applications of GaTe especially in optoelectronics and thermoelectrics, and provide a general methodology for the study of the anisotropy of light-matter interactions in 2D layered materials with in-plane anisotropy.

Lattice Vibration of Layered GaTe Single Crystals

“…The value of ∆ω = 49.5 cm −1 is close to the calculated frequency at 50.9 cm −1 . More interestingly, we also found the other two conjugated mode pairs by the S. Huang et al's [20] calculation results. In their Supplementary Information (Figure S3), for the calculated mode pairs, 25 (A u ω = 173.6 cm −1 ) and 23 (A u ω = 168.8 cm −1 ), 24 (B g ω = 172.7 cm −1 ) and 22 (B g ω = 167.6 cm −1 ), with the interlayer coupling frequency 40.5 cm −1 and 41.7 cm −1 , respectively, were observed.…”

“…Ten energy peaks are observed. Among them, the eight located at 109.6 cm −1 , 114.5 cm −1 , 151.7 cm −1 , 161.6 cm −1 , 175.2 cm −1 , 209.6 cm −1 , 267.1 cm −1 , 281.7 cm −1 match previous reports for monoclinic GaTe single crystals [18][19][20]24]. However, there is still controversy over the interpretation of the other two situated at 129.4 cm −1 and 141.8 cm −1 .…”

“…The possible explanation given by them was that the unit cell of GaTe might have only one layer. Yamamoto et al [20] carried out a position-dependent micro-Raman measurement with resolution of 1 µm at 18 K. Fourteen Raman active modes, including 11 A g and 3 B g modes, were identified from the 16 energy peaks, which are consistent with the results presented by Irwin et al [19]. The two rest peaks located at 178.8 cm −1 and 272.1 cm −1 were determined as the satellite peaks around the Raman shifts at 171.8 cm −1 and 270.5 cm −1 , respectively, while they attributed them to experimental conditions, instead of Davydov splitting in GaTe crystals.…”

“…Cerdeira et al [18] attributed the peak situated at 143 cm −1 to the particular vibration mode in GaTe crystal structure because of the strong Raman emission in pure GaTe. Most recently, S. Huang et al [20] carried out a much more detailed analysis about GaTe phonon vibration modes based on first-principles calculations, and they recommended that two peaks at 126 cm −1 and 142 cm −1 might originate from the double-resonant Raman mode which are the combinations of phonon around 60-70 cm −1 .…”

Mo6S3Br6: An Anisotropic 2D Superatomic Semiconductor

“…[6,[30][31][32][33][34] Figure 4a shows Raman spectra for parallel polarization (PP, top) and cross polarization (CP, bottom) configurations. [6,[30][31][32][33][34] Figure 4a shows Raman spectra for parallel polarization (PP, top) and cross polarization (CP, bottom) configurations.…”