GeC/GaN vdW Heterojunctions: A Promising Photocatalyst for Overall Water Splitting and Solar Energy Conversion

Abstract

Two-dimensional van der Waals (vdW) heterojunctions have been regarded as promising candidates for photocatalytic water splitting and solar energy conversion. Here, we propose a two-dimensional GeC/GaN vdW heterostructure, where the GaN monolayer and the GeC monolayer are stacked. The binding energy, phonon spectrum, and elastic constants demonstrate this material’s high dynamic and mechanical stability. Most notably, the GW band structure, GW + Bethe–Salpeter equation (BSE) optical absorption spectrum, and the band alignment of the density functional theory (DFT) scheme and empirical formula reveal that the GeC/GaN vdW heterostructures have a dramatically high optical absorption coefficient (∼105 cm–1) in the visible region and a suitable band edge with sufficiently large kinetic overpotentials of the hydrogen evolution reaction (ΔE c ≥ 1.945 eV) and the oxygen evolution reaction (ΔE v ≥ 1.244 eV). Photogenerated electrons and holes aggregate on the GeC monolayer and GaN monolayer surfaces, respectively, which could make this heterojunction a promising candidate for photocatalytic water splitting and solar energy conversion.

A new crystal family of GaNGeC quaternary compounds including direct band gap semiconductors and metals

“…In this study, most calculations pertaining to DFT (the standard density functional theory) and GW (the G 0 W 0 approximation) electronic band structures, 12,20,21 elastic constants and GW +BSE optical spectra (calculated using the combination of GW and Bethe Salpeter equation (BSE) method) 12,20,21 are performed using the Vienna Ab initio Simulation Package (VASP). 22,23 The projector augmented wave pseudo potential, 23 plane wave basis set, and Perdew Burke Ernzerhof (PBE) exchange correlation functional, 24 including vdW dispersive corrections 25 and spinorbit coupling (SOC), were applied.…”

“…where ε (ω) and ε (ω) are the real and the imaginary parts of the dielectric function ε(ω), respectively, and c is the speed of light in vacuum. 12,31 3 Results and discussions On the other hand, S-1, S-5, S-6, S-7 and S-8 present a hexagonal layered structure along the c-axis direction as they belong to the hexagonal crystal family. Specifically, S-1, S-5 and S-6 comprise GaN and GeC monolayers with different stacks, whereas S-7 and S-8 comprise GaC and GeN monolayers with different stacks.…”

“…Recently, GaN and GeC monolayers and GeC/GaN van der Waals (vdW) heterojunctions have been studied. 12 Moreover, GaN monolayers have been synthesized in experiments. [13][14][15][16] The research of the current paper provides a new way to investigate the GaNGeC system from bulk materials to thin films, the doublelayer vdW heterojunction and single-layer.…”

“…As listed in Table 1, S-1, S-2, S-3,S-4, S-5 and S-6 crystals are semiconductors, whereas S-7 and S-8 are metals. With regard to the semiconductors, the GW band structures 12,20,21 are shown, and for metals, the PBE band structures are displayed (Fig. 4).…”

“…7,8 On the other hand, recently, gallium nitride (GaN) and germanium carbide (GeC) monolayers and GeC/GaN van der Waals (vdW) heterojunctions have been studied. 12 GaN monolayers have been synthesized in experiments. [13][14][15][16] Moreover, threedimensional (3D) GaN has excellent electronic and optical properties, as a typical representative of third-generation semiconductors, and has been widely used in microwave communications, light-emitting diodes and laser diodes in the ultraviolet range.…”