Computational investigations of the metal/semiconductor NbS2/boron phosphide van der Waals heterostructure: effects of an electric field.

In this work, we design computationally the metal-semiconductor NbS2/BP heterostructure and investigate its atomic structure, electronic properties and contact barrier using first-principles prediction. Our results show that the M-S NbS2/BP heterostructure is energetically stable and is characterized by weak vdW interactions. Interestingly, we find that the combination of the metallic NbS2 and semiconducting BP layers leads to the formation of a M-S contact. The M-S NbS2/BP heterostructure exhibits a p-type Schottky contact and a low tunneling-specific resistivity of 3.98 × 10-10 Ω cm2, indicating that the metallic NbS2 can be considered as an efficient 2D electrical contact to the semiconducting BP layer to design NbS2/BP heterostructure-based electronic devices with high charge injection efficiency. The contact barrier and contact type in the M-S NbS2/BP heterostructure can be adjusted by applying an external electric field. The conversion from p-type ShC to n-type ShC can be achieved by applying a negative electric field, while the transformation from ShC to OhC type can be achieved under the application of a positive electric field. The conversion between p-type and n-type ShC and ShC to OhC type in the NbS2/BP heterostructure demonstrates that it can be considered as a promising material for next-generation electronic devices.

First principles prediction of electronic, mechanical, transport and optical properties of the silicane/Ga2SSe heterostructure.

In this work, we investigated the electronic structure, and mechanical, transport and optical properties of the van der Waals heterostructure formed from silicane (SiH) and Janus Ga2SSe monolayers using first-principles prediction. The out-of-plane symmetry in the Janus Ga2SSe monolayer leads to the formation of two different types of Ga2SSe/SiH heterostructure, namely SGa2Se/SiH and SeGa2S/SiH stacking patterns. All stacking patterns of the SiH/Ga2SSe heterostructure are thermodynamically, mechanically and energetically stable at room temperature. Furthermore, the generation of the SiH/Ga2SSe heterostructure gives rise to a reduction in the band gap, demonstrating that the electrons move faster from the valence bands to the conduction bands. The SiH/Ga2SSe heterostructure is a semiconductor with a direct band gap of about 0.68 or 0.95 eV, depending on the stacking pattern. The SiH/Ga2SSe heterostructure forms type-II band alignment for all stacking patterns, indicating that the photogenerated carriers are separated effectively, thus enhancing the photocatalytic performance. Moreover, the carrier mobilities for electrons and holes of the Ga2SSe/SiH heterostructure are higher than those of the constituent SiH and Ga2SSe monolayers in both the x and y directions, suggesting that the performances of electronic devices based on the Ga2SSe/SiH heterostructure would be excellent and reliable. The formation of the Ga2SSe/SiH heterostructure also gives rise to an enhancement of the absorption coefficient in both the visible and ultraviolet regions. Our findings could give valuable guidance for the design of high-efficiency devices based on the SiH/Ga2SSe heterostructure.

Theoretical prediction of structural, mechanical, and electronic properties of Janus GeSnX2 (X = S, Se, Te) single-layers.

The breaking of the vertical mirror symmetry in two-dimensional Janus structures has given rise to many outstanding features that do not exist in the original materials. In this work, we study the structural, mechanical, and electronic properties of Janus GeSnX2 (X = S, Se, Te) single-layers using density functional theory. The stability of the investigated Janus structures has been tested through the analysis of their phonon dispersions and elastic parameters. It is found that, with low in-plane stiffness, Janus GeSnX2 single-layers are more mechanically flexible than other two-dimensional materials and their mechanical properties exhibit very high anisotropy. All three single-layers are semiconductors and their bandgap can be altered easily by strain engineering. Due to the asymmetric structure, a vacuum level difference between the two sides is observed, leading to the difference in work function on the two sides of single-layers. Our findings not only provide necessary information about the physical properties of Janus GeSnX2 single-layers but also provide the impetus for further studies on these interesting materials both theoretically and experimentally.

Outstanding elastic, electronic, transport and optical properties of a novel layered material C4F2: first-principles study.

Motivated by very recent successful experimental transformation of AB-stacking bilayer graphene into fluorinated single-layer diamond (namely fluorinated diamane C4F2) [P. V. Bakharev, M. Huang, M. Saxena, S. W. Lee, S. H. Joo, S. O. Park, J. Dong, D. C. Camacho-Mojica, S. Jin, Y. Kwon, M. Biswal, F. Ding, S. K. Kwak, Z. Lee and R. S. Ruoff, Nat. Nanotechnol., 2020, 15, 59-66], we systematically investigate the structural, elastic, electronic, transport, and optical properties of fluorinated diamane C4F2 by using density functional theory. Our obtained results demonstrate that at the ground state, the lattice constant of C4F2 is 2.56 Å with chemical bonding between the C-C interlayer and intralayer bond lengths of about 1.5 Å which are close to the C-C bonding in the bulk diamond. Based on calculations for the phonon spectrum and ab initio molecular dynamics simulations, the structure of C4F2 is confirmed to be dynamically and thermally stable. C4F2 exhibits superior mechanical properties with a very high Young's modulus of 493.19 N m-1. Upon fluorination, the formation of C-C bonding between graphene layers has resulted in a comprehensive alteration of electronic properties of C4F2. C4F2 is a direct semiconductor with a large band gap and phase transitions are found when a biaxial strain or external electric field is applied. Interestingly, C4F2 has very high electron mobility, up to 3.03 × 103 cm2 V-1 s-1, much higher than other semiconductor compounds. Our findings not only provide a comprehensive insight into the physical properties of C4F2 but also open up its applicability in nanoelectromechanical and optoelectronic devices.

First-principles prediction of chemically functionalized InN monolayers: electronic and optical properties.

In this work, we consider the electronic and optical properties of chemically functionalized InN monolayers with F and Cl atoms (i.e., F-InN-F, F-InN-Cl, Cl-InN-F, Cl-InN-Cl monolayers) using first-principles calculations. The adsorption of the F and Cl atoms on the InN monolayer is determined to be chemically stable and the F-InN-F monolayer is most likely to occur. Our calculations show that the chemical functionalization with Cl and F atoms not only breaks the planar structure of InN monolayer but also increases its band gap. By using both Perdew, Burke, and Ernzerhof (PBE) and the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functionals, all four models of chemically functionalized InN monolayers are found to be semiconductors with direct energy gaps and these gaps depend on the constituent species. When the spin-orbit coupling (SOC) was included, the energy gap of these monolayers was reduced and an energy splitting was found at the Γ-point in the valence band. Chemically functionalized InN monolayers can absorb light in a wide region, especially the F-InN-F and Cl-InN-F monolayers have a strong ability to absorb the visible light. Our findings reveal that the chemically functionalized InN monolayers have potential applications in next-generation optoelectronic devices.