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Stacking different two-dimensional (2D) materials to form van der Waals (vdW) heterostructures has been considered as an effective strategy to realize new and exciting properties and innovative device applications in optoelectronics and electronics. In this work, we theoretically investigated the electronic properties of vdW heterostructures combined with different 2D MX materials (M  =  Ga, Ge, Sn, In; X  =  As, Se). Interestingly, SnAs/GaSe vdW heterostructure was screened from all the possible MX vdW heterostructures with the direct band gap (1.25 eV) within the visible light region, which perfectly falls into the optimum range for solar cells. Meanwhile, it was demonstrated that SnAs/GaSe vdW heterostructure has a typical type-II band alignment without strong interface hybridization, thus photogenerated electrons and holes could be effectively separated into opposite layers. In addition, the large band offset, small carrier effective mass, and high tunneling probability across the interface (16.24%) also guarantee its superiority in solar energy conversion. Our results suggest that SnAs/GaSe vdW heterostructure can be a new choice for low dimensional optoelectronic devices particularly for solar cells and pave the way for experimental verification in future. [ABSTRACT FROM AUTHOR]

We study two-dimensional (2D) germanene supported on Au(1 1 1) to determine the structural, electronic and interface interaction properties on the basis of first-principles electronic calculations. In light of the lattice commensurability, (2  ×  2)/(√7  ×  √7) and (√3  ×  √3)/(√7  ×  √7) germanene/Au(1 1 1) superstructures are obtained with low-binding energy. We find that the interface effects between germanene and Au(1 1 1) break the inversion symmetry of germanene to a significant extent. The electron accumulation layer between germanene and Au(1 1 1) bonds the adlayer and substrate together, indicating strong adsorption behavior. Charge transfer occurs from Au(1 1 1) to germanene with the formation of a dipole layer. In addition, the intense electronic orbital hybridization effects between germanene and Au(1 1 1) are revealed through the atomic projected band structures. Clearly, resonant behavior occurs between germanene p orbitals and Au(1 1 1) s orbitals. As germanene is peeled off from Au(1 1 1), the band structures are characterized as metallic, and in the absence of the Au(1 1 1) substrate the band structure of (√3  ×  √3) single layer germanene demonstrates a lower effective mass due to its higher geometrical symmetry, which is similar to that of planar graphene. This paper shows that Au(1 1 1) is a suitable candidate for the growth of germanene, and our results offer useful information for the application of germanene in electronic devices. [ABSTRACT FROM AUTHOR]