In this work, using density functional theory we investigated systematically the electronic properties and Schottky barrier modulation in a multilayer graphene/bilayer-GaSe heterostructure by varying the interlayer spacing and by applying an external electric field. At the equilibrium state, the graphene is bound to bilayer-GaSe by a weak van der Waals interaction with the interlayer distance d of 3.40 Å with the binding energy per carbon atom of -37.71 meV. The projected band structure of the graphene/bilayer-GaSe heterostructure appears as a combination of each band structure of graphene and bilayer-GaSe. Moreover, a tiny band gap of about 10 meV is opened at the Dirac point in the graphene/bilayer-GaSe heterostructure due to the sublattice symmetry breaking. The band gap opening in graphene makes it suitable for potential applications in nanoelectronic and optoelectronic devices. The graphene/bilayer-GaSe heterostructure forms an n-type Schottky contact with the Schottky barrier height of 0.72 eV at the equilibrium interlayer spacing. Furthermore, a transformation from the n-type to p-type Schottky contact could be performed by decreasing the interlayer distance or by applying an electric field. This transformation is observed when the interlayer distance is smaller than 3.30 Å, or when the applied positive external electric field is larger than 0.0125 V Å-1. These results are very important for designing new electronic Schottky devices based on graphene and other 2D semiconductors such as a graphene/bilayer-GaSe heterostructure.
Inspired by the successfully experimental synthesis of Janus structures recently, we systematically study the electronic, optical, and electronic transport properties of Janus monolayers In2XY (X/Y = S, Se, Te with X № Y) in the presence of a biaxial strain and electric field using density functional theory. Monolayers In2XY are dynamically and thermally stable at room temperature. At equilibrium, both In2STe and In2SeTe are direct semiconductors while In2SSe exhibits an indirect semiconducting behavior. The strain significantly alters the electronic structure of In2XY and their photocatalytic activity. Besides, the indirect-direct gap transitions can be found due to applied strain. The effect of the electric field on optical properties of In2XY is negligible. Meanwhile, the optical absorbance intensity of the Janus In2XY monolayers is remarkably increased by compressive strain. Also, In2XY monolayers exhibit very low lattice thermal conductivities resulting in a high figure of merit ZT, which makes them potential candidates for room-temperature thermoelectric materials.
The stacking of monolayers in the form of van der Waals heterostructures is a useful strategy for band gap engineering and the control of dynamics of excitons for potential nano-electronic devices. We performed first-principles calculations to investigate the structural, electronic, optical and photocatalytic properties of the SiC-MX (M = Mo, W and X = S, Se) van der Waals heterostructures. The stability of most favorable stacking is confirmed by calculating the binding energy and phonon spectrum. SiC-MoS is found to be a direct band gap type-II semiconducting heterostructure. Moderate in-plane tensile strain is used to achieve a direct band gap with type-II alignment in the SiC-WS, SiC-MoSe and SiC-WSe heterostructures. A difference in the ionization potential of the corresponding monolayers and interlayer charge transfer further confirmed the type-II band alignment in these heterostructures. Furthermore, the optical behaviour is investigated by calculation of the absorption spectra in terms of ε(ω) of the heterostructures and the corresponding monolayers. The photocatalytic response shows that the SiC-Mo(W)S heterostructures can oxidize HO to O. An enhanced photocatalytic performance with respect to the parent monolayers makes the SiC-Mo(W)Se heterostructures promising candidates for water splitting.
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