Polarization Photoelectric Conversion in Layered GeS

Abstract

Polarization photovoltaic effect is a unique character for an energy material with specific in‐plane anisotropy. Especially, if the energy material has a direct bandgap close to 1.6 eV, it will efficiently absorb full sunlight spectrum with specific axial polarization. In this study, polarized microtransmittance measurements of GeS multilayer with polarization angles ranging from θ = 0° (E || a) [through 90° (E || b)] to θ = 180° (E || a) have been studied near band edge. The polarized absorption edge follows a sinusoidal variation of E(θ) = 1.6 + 0.05⋅|sin(θ)| eV with respect to the angle change of the polarized absorption spectra. This anisotropic optical response is well reproduced by first‐principles calculations based on a combined Green's function technique, the GW–Bethe–Salpeter equation (BSE) approach. To characterize highly anisotropic band structure of layered GeS, polarized thermoreflectance measurement and first‐principles quasiparticle band‐structure calculations are also carried out. The interband transitions belonging to E ||a and E ||b polarizations are respectively identified. The polarized surface photovoltaic effects of a GeS Schottky solar cell are also tested. The special in‐plane optical anisotropy (along a and perpendicular to the a axis) renders GeS owning highly bi‐axial responsivity with respect to the c‐plane photoelectric conversion.

In‐Plane Optical Anisotropy of Low‐Symmetry 2D GeSe

“…GeSe is a representative layered group IV monochalcogenides and has a puckered structure similar to that of BP, as illustrated in Figure a. It belongs to the orthorhombic crystal structure ( a = 10.840 Å, b = 3.834 Å, and c = 4.390 Å) with Pnma 62 space group.…”

Polarization-tunable nonlinear absorption patterns from saturated absorption to reverse saturated absorption in anisotropic GeS flake and an application of all-optical switching

“…The constant parameter n, which is related to the material transition type, is 0.5 for layered GeS due to its direct transition [59]. However, owing to the small difference between E 1, and E 1, of GeS, more in-depth exploration of the angular dependence absorption edges of GeS could be acquired by derivative transmittance spectra method [39].…”

“…Moreover, GeS also possesses the largest ratio of figure-of-merit ZT (ZT armchair /ZT zigzag ), which is 1.434 (1.85/1.29), compared with 1.069 of SnSe (2.63/2.46), 1.074 of SnS (1.88/1.75), and 1.15 of GeSe (1.99/1.73) [38]. On the other hand, multilayer GeS is an anisotropic band-edge transition semiconductor with a direct-bandgap varying from 1.60 to 1.65 eV [39] and its electron mobility is 3680 cm 2…”

“…For instance, the photoluminescence (PL) was used to characterize the transition of GeS flakes near their band edges [45]. The polarization-dependent linear transmittance spectroscopy and PL effect were both properly studied to verify the anisotropic energy bands of GeS [39]. In the meantime, the Raman-scattering spectroscopy was used to identify the crystal orientation of 2D anisotropic materials (e.g., GeS and SnSe) [26,27,34,46].…”

“…) [39,47,48]. To this end, the experimental exploration of tunable optical and electronic properties in layered GeS is mainly focused on stain [44,49], defect/ doping [50], heterostructure [51][52][53] in experiments, with the theoretical calculations based on density functional theory (DFT) calculation [52,54].…”