Intriguing electronic and optical properties of two-dimensional Janus transition metal dichalcogenides

Abstract

Atomically thin Janus transition metal dichalcogenides (JTMDs) with an asymmetric structure have emerged as a new class of intriguing two-dimensional (2D) semiconductor materials. Using state-of-the-art density functional theory (DFT) calculations, we systematically investigate the structural, electronic, and optical properties of JTMD monolayers and heterostructures. Our calculated results indicate that the JTMD monolayers suffer from a bending strain but present high thermodynamic stability. All of them are semiconductors with a band-gap range from 1.37 to 1.96 eV. They possess pronounced optical absorption in the visible-light region and cover a large range of carrier mobilities from 28 to 606 cm2 V-1 s-1, indicating strong anisotropic characteristics. Significantly, some monolayer JTMDs (e.g., WSSe and WSeTe) exhibit superior mobilities than conventional TMD monolayers, such as MoS2. Moreover, the absolute band-edge positions of the JTMD monolayers are higher than the water redox potential, and most JTMD heterostructures have a type-II band alignment that contributes to the separation of carriers. Our work suggests that the 2D JTMD monolayers are promising for nanoelectronic, optoelectronic, and photocatalytic applications.

Enhanced electron–phonon scattering in Janus MoSSe

“…Consequently, the short MFPs of MoSSe here are attributed to the out-of-plane dipole moments. Our results also indicate that the MFPs of hot holes in MoSSe and MoS 2 are larger that hot electrons, which means hot holes transport more easily than hot electrons, agrees well with the results of the mobility analysis in [28,[43][44][45][46]. Furthermore, the MFPs along AM direction are much shorter than along ZZ direction, meaning the highly anisotropic propagation of hot carriers in MoSSe and MoS 2 .…”

Strain Engineering and Electric Field Tunable Electronic Properties of Janus MoSSe/WX2 (X = S, Se) van der Waals Heterostructures

“…[23] Except for the Janus MoSSe monolayer, first principles calculation showed that MXY (M ¼ Mo, W; X/Y ¼ S, Se, Te; and X 6 ¼ Y) monolayers are semiconductors with band gap values ranging from 1.37 to 1.96 eV. [24] Many MXY monolayers, such as MnSSe, show robust ferromagnetic ordering, large spin-polarization and high Curie temperature. [25] Heterostructures are the basis for device applications, such as FETs, solar cells, and light-emitting diodes.…”

Photoexcited charge carrier behaviors in solar energy conversion systems from theoretical simulations

“…As the heterostructures are formed between 2D materials, interface reduces to actually 1D, referred to as interline. In the in‐plane heterostructures composed of 2D TMDCs, two TMDCs are linked by covalent bonds rather than the weak vdW forces in vertical vdW bilayers, ensuring the epitaxial quality and boosts the optical and electronic performance . In particular, the intrinsic p–n junction behavior has been demonstrated in in‐plane heterostructures of 2D TMDCs.…”

“…It has been identified that the excitonic properties of dye molecules/quantum dots are difficult to control, therefore, 2D TMDCs provide new choices and present superiorities. On the basis of the model system composing of single Au nanotriangles and monolayer WS 2 , controllable Fano resonances and plasmon–exciton coupling was previously realized . It is of interest that tunable transition from plasmon–exciton coupling of different strength can be achieved.…”

“…In order to realize high light–energy conversion efficiency, a variety of strategies or concepts have been developed or proposed to improve the photoelectrochemical performance of photocatalysts via addition of electron donor (hole scavenger), controlled incorporation of oxygen vacancies, noble metal loading, metal ion doping, anion doping, dye sensitization, and formation of composite semiconductors . In recent years, more and more two‐dimensional (2D) materials have been predicted, synthesized, transferred and characterized since the realization of graphene, such as transition metal dichalcogenides (TMDCs), transition metal carbides and nitrides (MXenes), group‐III and group‐IV metal monochalcogenides, black phosphorus (phosphorene, BP), and so on . In respect to potential photocatalytic applications, 2D monolayer materials find their advantages like high specific surface area, strong light absorption, high charge carrier mobility, unique electronic structures, and chemical stability.…”