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In this study, based on first-principles calculation, the structural, electronic, interfacial, and optical properties of two-dimensional (2D) semiconductor vertical heterostructure constructed by g-GaN and Mg(OH)2 are addressed. The g-GaN/Mg(OH)2 heterostructure is discovered to be formed by van der Waals (vdW) forces and possesses a type-II band structure which can promote the separation of photogenerated electron–holes constantly. At the same time, the calculated band edge positions of the heterostructure are decent to induce the oxidation and reduction reactions for water splitting at pH 0. Gibb's free energy change in the redox reaction for the g-GaN/Mg(OH)2 vdW heterostructure is further investigated that the heterostructure can act as a suitable catalyst in hydrogen evolution reaction and oxygen evolution reaction for water splitting. The charge-density difference and the potential drop are calculated across the interface of the g-GaN/Mg(OH)2 vdW heterostructure, and the potential drop can induce a large built-in electric field, which is also a boost to prevent the recombination of the photogenerated charges. Finally, the applied external biaxial strain is studied that it can improve the optical absorption performance of the g-GaN/Mg(OH)2 vdW heterostructure. This study provides a possibility of method to design the 2D vdW heterostructure as a photocatalyst to decompose water. [ABSTRACT FROM AUTHOR]

Based on first-principles calculations, we systematically investigate the electronic and optical properties of van der Waals (vdW) heterostructures composed of graphene-like gallium nitride (g-GaN) and transition metal dichalcogenides (TMDs). The investigated vdW heterostructures (g-GaN/MoS 2 , g-GaN/WS 2 , g-GaN/MoSe 2 , and g-GaN/WSe 2) are all semiconductors with direct bandgap. In particular, both the g-GaN/MoS 2 and g-GaN/WS 2 vdW heterostructures possess type-II band alignment, which will facilitate the separation of photogenerated carriers, and enhance their lifetime. Furthermore, band edge positions of these two heterostructures satisfied both water oxidation and reduction energy requirements, suggesting the potential in photocatalysts for water splitting. In addition, both g-GaN/MoS 2 and g-GaN/WS 2 vdW heterostructures exhibit a high electron mobility, which ensure that the redox reactions for water splitting will be effectively proceeded. More importantly, they show significant absorption peaks in the visible light region, leading to highly efficient utilization of the solar energy. These fascinating properties render the g-GaN/MoS 2 and g-GaN/WS 2 vdW heterostructures high-efficiency photocatalysts for water splitting. Unlabelled Image • Many g-GaN/TMD vdW heterostructures are direct-bandgap semiconductors. • Both g-GaN/MoS 2 and g-GaN/WS 2 form type-II heterostructure. • g-GaN/MoS 2 and g-GaN/WS 2 satisfy both water oxidation and reduction potential levels. • Both g-GaN/MoSe 2 and g-GaN/WSe 2 vdW heterostructures have type-I band alignment. [ABSTRACT FROM AUTHOR]

Abstract Four vertical heterostructures based on two-dimensional transition-metal dichalcogenides (TMDs) – MoS 2 /GeC, MoSe 2 /GeC, WS 2 /GeC, and WSe 2 /GeC, were studied by density functional theory calculations to investigate their structure, electronic characteristics, principle of photogenerated electron–hole separation, and optical-absorption capability. The optimized heterostructures were formed by van der Waals (vdW) forces and without covalent bonding. Their most stable geometric configurations and band structures display type-II band alignment, which allows them to spontaneously separate photogenerated electrons and holes. The charge difference and built-in electric field across the interface of these vdW heterostructures also contribute to preventing the photogenerated electron–hole recombination. Finally, the high optical absorption of the four TMD-based vdW heterostructures in the visible and near-infrared regions indicates their suitability for photocatalytic, photovoltaic, and optical devices. Highlights • The most stable structures of the vertical heterostructures of TMDs/GeC are obtained. • Van der Waals interaction are found in these heterostructures. • Type-II band alignment are addressed in all the vdW heterostructures which can separate the photogenerated-charge. • All the structures are suitable for photocatalytic, photovoltaic, and optical devices. • All the structures show high optical absorption in the visible and NIR ranges. [ABSTRACT FROM AUTHOR]

After the discovery of graphene, a lot of research has been conducted on two-dimensional (2D) materials. In order to increase the performance of 2D materials and expand their applications, two different layered materials are usually combined by van der Waals (vdW) interactions to form a heterostructure. In this work, based on first-principles calculation, some charming properties of the heterostructure constructed by Hf2CO2, AlN and GaN are addressed. The results show that Hf2CO2/AlN and Hf2CO2/GaN vdW heterostructures can keep their original band structure shape and have strong thermal stability at 300 K. In addition, the Hf2CO2/MN heterostructure has I-type band alignment structure, which can be used as a promising light-emitting device material. The charge transfer between the Hf2CO2 and AlN (or GaN) monolayers is 0.1513 (or 0.0414) |e|. The potential of Hf2CO2/AlN and Hf2CO2/GaN vdW heterostructures decreases by 6.445 eV and 3.752 eV, respectively, across the interface. Furthermore, both Hf2CO2/AlN and Hf2CO2/GaN heterostructures have remarkable optical absorption capacity, which further shows the application prospect of the Hf2CO2/MN heterostructure. The study of this work provides theoretical guidance for the design of heterostructures for use as photocatalytic and photovoltaic devices. [ABSTRACT FROM AUTHOR]

In this paper, the optical and electronic properties of WSSe/BSe heterostructure are investigated by first-principles calculations. The most stable stacking pattern of the WSSe/BSe compounds is formed by van der Waals interaction with a thermal stability proved by ab initio molecular dynamics simulation. The WSSe/BSe heterostructure exhibits a type-I band alignment with direct bandgap of 2.151 eV, which can improve the effective recombination of photoexcited holes and electrons. Furthermore, the band alignment of the WSSe/BSe heterostructure can straddle the water redox potential at pH 0–8, and it has a wide absorption range for visible light. In particular, the solar-to-hydrogen efficiency of the WSSe/BSe heterostructure is obtained at as high as 44.9% at pH 4 and 5. All these investigations show that the WSSe/BSe heterostructure has potential application in photocatalysts to decompose water. [ABSTRACT FROM AUTHOR]

• The most stable stacking structure of the ZnO/Mg(OH) 2 van der Waals heterostructure is obtained. • Type-II band alignment is addressed in ZnO/Mg(OH) 2 vdW heterostructure which can separate the photogenerated-charge. • The ZnO/Mg(OH) 2 vdW heterostructure has decent band edge positions for the redox reaction of water splitting at pH 0. • The ZnO/Mg(OH) 2 vdW heterostructure has excellent optical absorption property near the visible-light region. In this study, the structural, electronic and optical properties of the two-dimensional heterostructure based on ZnO and Mg(OH) 2 are investigated by first-principle calculations. The ZnO/Mg(OH) 2 heterostructure, formed by van der Waals (vdW) interaction, possesses a type-II band structure, which can separate the photogenerated electron–holes constantly. The heterostructure has decent band edge positions for the redox reaction to decompose the water at pH 0 and 7. As for the interfacial properties of the heterostructure, the trend of band bending of the ZnO and Mg(OH) 2 layers in the heterostructure is addressed, which will result a built-in electric field. Besides, the charge-density difference and potential drop across the interface of the ZnO/Mg(OH) 2 vdW heterostructure are also calculated. Finally, the heterostructure is demonstrated that it not only has excellent ability to capture the light near the visible spectrum region, but also can improve the optical performance for the monolayered ZnO and Mg(OH) 2. [ABSTRACT FROM AUTHOR]