Band alignment and optoelectronic characteristics of 2D Janus heterostructures

Abstract

Two-dimensional (2D) Janus semiconductor materials have attracted widespread research interest due to their unique asymmetric structures and promising optoelectronic applications. Here, we investigate the interfacial effects on band alignment and photodetection performance by constructing van der Waals heterostructures (vdWHs) based on monolayer CrS₂ and Janus MoSO, alongside engineering the interlayer distance, biaxial strain, and external electric field. The S-terminated and O-terminated interfaces induce direct and indirect band structures, respectively, while maintaining a robust type-II band alignment. Moreover, the O-terminated interface vdWH photodetector exhibits higher photocurrent density and external quantum efficiency compared with the S-terminated counterpart. These results provide an effective strategy for designing interface-engineered optoelectronic devices based on 2D Janus semiconductors.

Graphical abstract

Keywords

Janus MoSO / vdW heterostructure / band alignment / photodetection characteristics

1 Introduction

Two-dimensional (2D) Janus materials exhibit unique properties, such as the piezoelectric effect [1, 2], photovoltaic effect [3, 4], and Rashba splitting [5, 6], owing to their broken structural symmetry. These characteristics endow them with significant potential for applications in novel optoelectronic devices [7−10]. Notably, channels based on 2D transition metal dichalcogenides (TMDs) possess isolated band features that can induce a super-exponential reduction in off-state leakage current [11, 12]. Among various 2D Janus materials, Janus TMDs, with their excellent electronic and piezoelectric characteristics, are particularly promising for high-performance field-effect transistors (FETs), ultra-sensitive photodetectors, and valley electronic devices [13−16]. For instance, SnSSe-based FETs demonstrate significantly higher mobility and conduction current than their SnS₂-based counterparts [17]. Excitons in Janus TMDs form 30% faster than in pristine TMDs [18], and photoelectric devices based on Janus MoSSe exhibit pronounced spontaneous photocurrent and high light response [19].

Constructing van der Waals heterostructures (vdWHs) presents a viable strategy for tailoring material characteristics [20−22]. For example, the built-in electric field in an In₂STe/GeH vdWH enhances photocurrent conduction [23]. A Ge/SeMoS vdWH shows stronger optical absorption over a wider photon energy range compared to its monolayer constituents [24]. The GeC/SnSSe vdWH acts as an efficient photocatalyst, and its photocurrent can be increased by 40% under tensile strain [25]. Moreover, the construction of type-II band alignment, such as in CsPbI₃/TMDC and h-BNC/SWSe vdWHs, is particularly effective for optimizing charge separation and enhancing optoelectronic device performance [26, 27]. However, studies on the interface effects on electronic and photodetection characteristics of 2D Janus vdWHs remain relatively few.

The 2D Janus MoSO exhibits promising optoelectronic characteristics, including strong intrinsic polarization, stability under large strain [16], and pronounced vertical piezoelectric properties suitable for energy-harvesting and self-powered wearable devices [17]. Motivated by these properties, this study investigates the electronic and optical properties of MoSO-based vdWHs. Given the small lattice mismatch between Janus MoSO and CrS₂, we construct Janus MoSO/CrS₂ vdWHs with two distinct contact interfaces (S-terminated and O-terminated) as a model system to probe interfacial contact, band structure, and photocurrent. Our results show that both interface configurations form stable structures with a type-II band alignment, which remains robust under modulation of interlayer coupling, biaxial strain, and external electric fields. Furthermore, the designed photodetectors based on these heterostructures exhibit high external quantum efficiency (EQE) and photocurrent density.

2 Calculation method

All calculations were performed using the Vienna ab initio Simulation Package (VASP), where the electron exchange correlation was approximated by the generalized gradient approximation (GGA) of Perdew−Burke−Ernzerhof (PBE) [28, 29]. The electron-ion potential was described by the projector-augmented wave (PAW) method [30]. The Heyd−Scuseria−Ernzerhof (HSE06) functional was employed to obtain more accurate band gaps [31]. The vdW interactions were corrected using the DFT-D3 method, and dipole correction was considered. The vacuum layer thicker than 20 Å was applied along the out-of-plane direction. A plane-wave cutoff energy of 500 eV was used. The Brillouin zone was sampled with a 13 × 13 × 1 Γ-centered k-point grid [32]. Structural relaxations were conducted until the forces on each atom were less than 0.01 eV/Å and the total energy change between consecutive steps was below 10⁻⁵ eV.

The photocurrent densities of the designed devices were calculated using the non-equilibrium Green’s function, as implemented in the Quantum ATK software [33, 34]. The Brillouin zone was sampled with an 11 × 1 × 182 k-point grid, and the density mesh cutoff was set to 125 Hartree. All simulations were performed at a temperature of 300 K. The direction of incident light was perpendicular to the device, and the current flow was defined from the source to the drain electrode.

3 Results and discussion

3.1 The construction of Janus OMoS/CrS₂ and SMoO/CrS₂ vdWHs

The atomic structures of the isolated Janus MoSO and CrS₂ monolayer are depicted in Figs. 1(a) and (b), respectively. The optimized lattice constants of the MoSO monolayer and CrS₂ monolayer are a = b = 3.00 Å and a = b = 3.04 Å, in agreement with previously reported values [35−38]. The lattice mismatch between CrS₂ and MoSO is only 1.32%. Different initial stacking configurations were considered to determine the most stable stacking configuration, as illustrated in Fig. S1. According to the constituent contact interface, the contract vdWHs are categorized into two types: the S-terminated interface (denoted as the SMoO/CrS₂ vdWH) and the O-terminated interface (denoted as the OMoS/CrS₂ vdWH).

The stability of the constructed Janus OMoS/CrS₂ and SMoO/CrS₂ vdWHs was evaluated by calculating the binding energy, defined as

(1)E_{\mathrm{b}}=\left(E_{\mathrm{v}\mathrm{d}\mathrm{W}\mathrm{H}}-E_{{\mathrm{C}\mathrm{r}\mathrm{S}}_2}-E_{\mathrm{M}\mathrm{o}\mathrm{S}\mathrm{O}}\right)/A,

where E_{\mathrm{v}\mathrm{d}\mathrm{W}\mathrm{H}}, E_{{\mathrm{C}\mathrm{r}\mathrm{S}}_2}, and E_{\mathrm{M}\mathrm{o}\mathrm{S}\mathrm{O}} are the total energies of the heterostructure, the isolated CrS₂ monolayer, and the isolated MoSO monolayer, respectively, and A is the surface area. The calculated binding energies for all considered stacking configurations are listed in Table S1. The most stable stacking configuration of Janus OMoS/CrS₂ and SMoO/CrS₂ vdWHs is AD1 and AC2, with binding energies of −229.15 and −226.04 meV/Ų, respectively. All subsequent analyses are based on these most stable configurations. To further assess the dynamic stability, ab initio molecular dynamics (AIMD) simulations were performed at 300 K. As shown in Fig. S2, the total energy of each system fluctuates within a small, stable amplitude throughout the simulation. These results confirm that both the MoSO/CrS₂ and MoOS/CrS₂ vdWHs are structurally stable at room temperature.

3.2 Electronic properties of OMoS/CrS₂ and SMoO/CrS₂ vdWHs

To elucidate the electronic properties of the Janus OMoS/CrS₂ and SMoO/CrS₂ vdWHs, we first examine the band structures of their constituent monolayers. As shown in Figs. 1(d) and (e), the Janus MoSO monolayer exhibits an indirect bandgap of 1.61 eV, while the CrS₂ monolayer possesses a direct bandgap of 1.34 eV, as calculated using the HSE06 functional. These values are consistent with previous reports [35−37]. Figures 1(f) and (g) present the band structures of Janus OMoS/CrS₂ and SMoO/CrS₂ vdWHs. The OMoS/CrS₂ vdWH maintains an indirect bandgap of 0.53 eV, whereas the SMoO/CrS₂ vdWH shows a direct bandgap of 0.28 eV (HSE06). Notably, both heterostructures exhibit a type-II band alignment. For the OMoS/CrS₂ vdWH, the conduction band minimum (CBM) is dominated by the CrS₂ layer, while the valence band maximum (VBM) is primarily contributed by the MoSO layer. In contrast, for the SMoO/CrS₂ vdWH, the CBM originates from the MoSO layer, and the VBM from the CrS₂ layer. Furthermore, as demonstrated by the calculations in Fig. S3, the SOC effect has a negligible effect on the nature of band structures.

To further explore the formation mechanism of type-II band alignment in OMoS/CrS₂ and SMoO/CrS₂ vdWHs, we analyze the work functions and band alignments of the constituent monolayers, as shown in Figs. 2(a) and (b). The work function can be calculated as W=E_{\mathrm{v}\mathrm{a}\mathrm{c}}-E_{\mathrm{F}}, where E_{\mathrm{v}\mathrm{a}\mathrm{c}} and E_{\mathrm{F}} represent the vacuum energy level and Fermi energy, respectively. The calculated electrostatic potentials of the isolated MoSO and CrS₂ monolayers, as well as the heterostructures, are presented in Figs. S4 and S5. The work functions are determined to be 6.17 eV for the CrS₂ monolayer and 5.14 (7.44) eV for the S-terminated (O-terminated) side of the Janus MoSO monolayer. This indicates that the work function of the S-terminated side of MoSO is lower than that of CrS₂, while that of the O-terminated side is higher. Consequently, electrons flow from the MoSO layer to the CrS₂ layer in the OMoS/CrS₂ vdWH, whereas the direction reverses in the SMoO/CrS₂ vdWH, with electrons transferring from CrS₂ to MoSO. The corresponding built-in electric field directions are illustrated in Figs. 2(a) and (b), confirming the type-II band alignment in both systems.

For a quantitative assessment of the charge transfer, we calculate the Bader charge and the plane-average charge density difference Δρ(z). The Δρ(z) is defined as

(2)\mathrm{\Delta }\rho \left(z\right)=\rho {\left(z\right)}_{\mathrm{v}\mathrm{d}\mathrm{W}\mathrm{H}}-\rho {\left(z\right)}_{{\mathrm{C}\mathrm{r}\mathrm{S}}_2}-\rho {\left(z\right)}_{\mathrm{M}\mathrm{o}\mathrm{S}\mathrm{O}},

where \rho {\left(z\right)}_{\mathrm{v}\mathrm{d}\mathrm{W}\mathrm{H}}, \rho {\left(z\right)}_{{\mathrm{C}\mathrm{r}\mathrm{S}}_2} and \rho {\left(z\right)}_{\mathrm{M}\mathrm{o}\mathrm{S}\mathrm{O}} are the plane-averaged charge densities of the heterostructure, the isolated CrS₂ monolayer, and the isolated MoSO monolayer, respectively. Bader charge analysis reveals a net transfer of 0.0023 e from MoSO to CrS₂ in the OMoS/CrS₂ vdWH, and of 0.0173 e from CrS₂ to MoSO in the SMoO/CrS₂ vdWH. This result is corroborated by the plane-averaged charge density difference profiles shown in Fig. S5.

Moreover, under light irradiation, electrons in the valence band of the OMoS/CrS₂ and SMoO/CrS₂ heterostructures absorb photons and are excited to the conduction band, generating electron-hole pairs. Due to the type-II band alignment, these photogenerated carriers are spatially separated. In the OMoS/CrS₂ vdWH, photogenerated electrons transfer from the MoSO to the CrS₂, and photogenerated holes transfer from CrS₂ to MoSO. Conversely, for SMoO/CrS₂ vdWH, photogenerated electrons flow from CrS₂ to MoSO, and photogenerated holes flow from MoSO to CrS₂. Therefore, the type-II band alignment is advantageous for the separation of photogenerated electrons and holes. This efficient spatial separation of electrons and holes, facilitated by the type-II alignment, is highly beneficial for suppressing recombination and enhancing optoelectronic performance.

3.3 Effects of interlayer coupling, biaxial strain, and electric field

It is well-known that the electronic and optical properties of vdWHs can be effectively tuned through external means such as interlayer coupling, strain, and electric fields [39−43]. For instance, tensile strain has been shown to enhance the photocurrent in GeC/SnSSe vdWHs [25]. Biaxial strain can significantly modulate excitonic absorption peaks [44]. Furthermore, external electric fields and interlayer coupling are effective approaches for engineering the electronic structure of systems like C₃N₄/MoSi₂N₄ vdWH [45]. Motivated by these precedents, we systematically investigate the evolution of the band structures in OMoS/CrS₂ and SMoO/CrS₂ vdWHs under varying interlayer distances, biaxial strains, and external electric fields.

To understand the effect of interlayer coupling, we first examine the dependence of the binding energy and band gap on the interlayer distance, as shown in Figs. 2(c)−(e). As shown in Fig. 2(d), the binding energy of both heterostructures increases when the interlayer distance deviates from its equilibrium value, either by compression or stretching. The band gap of OMoS/CrS₂ vdWH exhibits a monotonic increase with increasing interlayer distance. For the SMoO/CrS₂ vdWH, the band gap first rises from 0.259 eV to a maximum of 0.286 eV and then declines upon further separation (all values are listed in Table S2). To gain further insight into the effect of interlayer coupling, the corresponding band structures under varying interlayer distances are presented in Fig. S6. Notably, the band alignment type remains unchanged across the entire range of distances studied for both systems. These findings demonstrate the high structural and electronic robustness of the designed vdWHs against variations in interlayer coupling.

Next, we investigate the influence of biaxial strain on the band structures of the OMoS/CrS₂ and SMoO/CrS₂ vdWHs. The applied strain (ε) is defined as \epsilon =\left(a-a_0\right)/a_0, where a and a₀ are the lattice parameters of the strained and unstrained systems, respectively. Negative and positive values denote compressive and tensile strain, respectively. A strain range from −5% to +5% with an increment of 2% is employed to systematically examine its impact on electronic properties. As illustrated in Figs. 3(b) and (c), the conduction-band offset (ΔE_c) decreases for both heterostructures across the applied strain range. In contrast, the valence-band offset (ΔE_v) exhibits different trends: it increases for the OMoS/CrS₂ vdWH but decreases for the SMoO/CrS₂ vdWH. Larger band offsets generally facilitate the spatial separation of photogenerated electron−hole pairs under illumination. Consequently, tensile strain is found to promote charge carrier separation in both types of vdWHs. Furthermore, the band gaps and detailed band structures under different strains are provided in Table S2 and Fig. 4, respectively.

Finally, the influence of an external electric field applied perpendicularly to the heterostructures (along the vacuum layer direction) is investigated. As schematically shown in Fig. 3(d), the positive field direction is defined as pointing from the CrS₂ layer to the MoSO layer. The applied external electric field strength is varied from −0.5 to +0.5 V/Å with a step of 0.2 V/Å. The projected band structures in Fig. S6 reveal that the band gaps of both vdWHs are highly sensitive to the applied field. Specifically, under a positive external electric field, the band gap of the OMoS/CrS₂ vdWH increases linearly, whereas that of the SMoO/CrS₂ vdWH decreases linearly. Conversely, a negative external electric field induces an opposite linear trend: the band gap decreases for OMoS/CrS₂ vdWH and increases for SMoO/CrS₂ vdWH. Furthermore, the evolution of the band offsets with the external electric field is presented in Figs. 3(e) and (f). A larger band offset, which promotes charge separation, is achieved in the OMoS/CrS₂ vdWH under a negative external electric field, and in the SMoO/CrS₂ vdWH under a positive external electric field. In summary, the efficient spatial separation of photogenerated electrons and holes can be effectively modulated and enhanced through interlayer coupling, biaxial strain, and external electric fields. This tunability underscores the great potential of the designed OMoS/CrS₂ and SMoO/CrS₂ vdWHs for application in high-performance optoelectronic devices.

3.4 Optoelectronic characteristics of photodetector applications

To evaluate their potential for photodetector applications, we calculated the photocurrent density of the Janus MoSO monolayer, the CrS₂ monolayer, and the OMoS/CrS₂ and SMoO/CrS₂ vdWHs using the Quantum ATK software package [46]. The simulated device architecture based on the OMoS/CrS₂ vdWH is depicted in Fig. 5(a), comprising source and drain electrodes with a length of 1.07 nm each, and a central scattering region of 7.25 nm in length. The device is illuminated by linearly polarized light with a power density of 16 mW/mm².

Figure 5(c) illustrates the photocurrent density as a function of wavelength for the constituent monolayers and the vdWHs. The photocurrent densities of both the OMoS/CrS₂ and SMoO/CrS₂ vdWHs significantly exceed those of the isolated MoSO and CrS₂ monolayers, which is attributed to the efficient separation of photogenerated electron-hole pairs facilitated by the type-II band alignment. Significant photocurrent peaks are observed at approximately 427 nm and 375 nm for the OMoS/CrS₂ and MoSO/CrS₂ vdWHs, with maximum values reaching 6.53 nA/m and 9.01 nA/m, respectively. According to Fermi’s Golden Rule, the probability of electron transitions is proportional to the density of states (DOS) [47]. As shown in Fig. 5(b), the projected density of states (PDOSs) for the OMoS/CrS₂ vdWH exhibits prominent peaks at approximately −1.2 eV and 1.7 eV, while those for the SMoO/CrS₂ vdWH are located at about −1.6 eV and 1.7 eV. The energy differences between these respective valence and conduction band peaks are approximately 2.9 eV and 3.3 eV. These energy values correspond to the observed photocurrent peaks at 427 nm (2.9 eV) and 375 nm (3.3 eV), confirming that the prominent photoresponse originates from electron transitions between these high PDOS peaks.

The external quantum efficiency (EQE) is a key parameter for photodetectors, quantifying the ratio of collected charge carriers to incident photons. It is calculated using the formula E=R_{\mathrm{p}\mathrm{h}}hc/(e\lambda ), where λ is the wavelength of incident light, R_ph is the photoresponsivity, h is Planck’s constant, c is the speed of light, and e is the elementary charge. As shown in Fig. 5(d), the calculated EQE reaches 5.6% for the SMoO/CrS₂ vdWH device and 7.8% for the OMoS/CrS₂ vdWH device. These values significantly surpass those of their constituent monolayers (3.17% for CrS₂ and 0.59% for MoSO). This enhancement clearly demonstrates that constructing vdWHs is an effective strategy for improving EQE, and further indicates that the interfacial configuration (S-terminated and O-terminated) plays a decisive role in device performance. Notably, the EQE of the SMoO/CrS₂ device (7.8%) compares favorably with other reported 2D photodetectors, such as MoSe₂/WSe₂ lateral heterostructure (4.3%) [48], the WSe₂/MoS₂ vdWH (1.5%) [49], and β-AsP (6.1%) [50]. Thus, the SMoO/CrS₂ vdWH device exhibits significant performance advantages, and its stable properties offer more potential applications in multifunctional photodetectors. Given its superior EQE alongside the structural and electronic robustness demonstrated earlier, the SMoO/CrS₂ vdWH emerges as a highly promising candidate for high-performance, multifunctional photodetectors.

4 Conclusions

In summary, we have designed and systematically investigated vdWHs by combining a CrS₂ and Janus MoSO monolayer via two distinct contact interfaces (S-terminated and O-terminated). Both OMoS/CrS₂ and SMoO/CrS₂ vdWHs exhibit stable structures and possess a type-II band alignment, which drives opposite directions of interfacial charge transfer. Remarkably, this type-II alignment is robust against significant variations in interlayer coupling, biaxial strain, and external electric field, demonstrating excellent structural and electronic stability. Notably, the photodetector based on the O-terminated interface vdWH achieves a higher photocurrent density than its S-terminated counterpart. This work elucidates the critical role of interfacial configuration in determining the properties of 2D Janus vdWHs. Our findings provide a viable strategy and material candidates for designing efficient, stable, and tunable photodetectors through interface engineering.

References

[1] Q. Ma , G. Yang , B. Wang , and Y. Liu , Large out-of-plane piezoelectric effect in a Janus ferromagnetic semiconductor monolayer of CrOFBr, Phys. Rev. B 110(6), 064430 (2024)

[2] T. V. Vu , N. T. Hiep , H. V. Phuc , B. D. Hoi , A. I. Kartamyshev , and N. N. Hieu , Raman response, piezoelectricity, and transport properties of the two-dimensional Janus HfSiX₃H (X=N/P/As) semiconductors: A first-principles study, Phys. Rev. B 110(23), 235403 (2024)

[3] L. Li , Z. X. Yang , T. Huang , H. Wan , W. Y. Chen , T. Zhang , G. F. Huang , W. Hu , and W. Q. Huang , Doping-free Janus homojunction solar cell with efficiency exceeding 23%, Appl. Phys. Lett. 125(22), 223904 (2024)

[4] A. Strasser , H. Wang , and X. Qian , Nonlinear optical and photocurrent responses in Janus MoSSe monolayer and MoS₂–MoSSe van der Waals heterostructure, Nano Lett. 22(10), 4145 (2022)

[5] A. Bordoloi and S. Singh , Exploring nonlinear Rashba effect and spin Hall conductivity in Janus MXenes W₂COX(X=S , and Se , Te), Phys. Rev. B 110(24), 245421 (2024)

[6] S. Karmakar , R. Biswas , and T. Saha-Dasgupta , Giant Rashba effect and nonlinear anomalous Hall conductivity in a two-dimensional molybdenum-based Janus structure, Phys. Rev. B 107(7), 075403 (2023)

[7] L. Du , T. Hasan , A. Castellanos-Gomez , G. B. Liu , Y. Yao , C. N. Lau , and Z. Sun , Engineering symmetry breaking in 2D layered materials, Nat. Rev. Phys. 3(3), 193 (2021)

[8] J. Kopaczek , M. Y. Sayyad , C. L. Wu , R. Sailus , R. Kudrawiec , and S. A. Tongay , Impact of polarization field architecture on excitonic properties of 2D Janus homobilayers, Nano Lett. 24(49), 15700 (2024)

[9] W. Ahmad , Y. Wang , J. Kazmi , U. Younis , N. M. Mubarak , S. H. Aleithan , A. I. Channa , W. Lei , and Z. Wang , Janus 2D transition metal dichalcogenides: Research progress, optical mechanism and future prospects for optoelectronic devices, Laser Photonics Rev. 19(6), 2400341 (2025)

[10] M. J. Varjovi,M. Yagmurcukardes,F. M. Peeters,E. Durgun, Janus two-dimensional transition metal dichalcogenide oxides: First-principles investigation of WXO monolayers with X = S, Se, and Te, Phys. Rev. B 103(19), 195438 (2021)

[11] H. Qu , S. Zhang , J. Cao , Z. Wu , Y. Chai , W. Li , L. J. Li , W. Ren , X. Wang , and H. Zeng , Identifying atomically thin isolated-band channels for intrinsic steep-slope transistors by high-throughput study, Sci. Bull. (Beijing) 69(10), 1427 (2024)

[12] W. Chu , X. Zhou , Z. Wang , X. Fan , X. Guo , C. Li , J. Yue , F. Ouyang , J. Zhao , and Y. Zhou , Stable alkali halide vapor assisted chemical vapor deposition of 2D HfSe₂ templates and controllable oxidation of its heterostructures, Front. Phys. (Beijing) 19(3), 33212 (2024)

[13] R. Guo , R. Zhao , Y. Ge , Y. Liu , W. Wan , Formation of 2D GaXY (X = S , Se, Y = F , and Cl , Br, I) with enhanced piezoelectricity via decomposition of Ga-monochalcogenide by halogenation, Appl. Phys. Lett. 123(6), 063102 (2023)

[14] M. M. Petrić , M. Kremser , M. Barbone , Y. Qin , Y. Sayyad , Y. Shen , S. Tongay , J. J. Finley , A. R. Botello-Méndez , and K. Müller , Raman spectrum of Janus transition metal dichalcogenide monolayers WSSe and MoSSe, Phys. Rev. B 103(3), 035414 (2021)

[15] L. Zhu , Y. Zhang , P. Lin , Y. Wang , L. Yang , L. Chen , L. Wang , B. Chen , and Z. L. Wang , Piezotronic effect on Rashba spin-orbit coupling in a ZnO/P₃HT nanowire array structure, ACS Nano 12(2), 1811 (2018)

[16] F. Langer , C. P. Schmid , S. Schlauderer , M. Gmitra , J. Fabian , P. Nagler , C. Schüller , T. Korn , P. G. Hawkins , J. T. Steiner , U. Huttner , S. W. Koch , M. Kira , and R. Huber , Lightwave valleytronics in a monolayer of tungsten diselenide, Nature 557(7703), 76 (2018)

[17] S. M. He , J. Y. Zhuang , C. F. Chen , R. K. Liao , S. T. Lo , Y. F. Lin , and C. Y. Su , Plasma-driven selenization for electrical property enhancement in Janus 2D materials, Small Methods 8(10), 2400150 (2024)

[18] T. Zheng , Y. C. Lin , Y. Yu , P. Valencia-Acuna , A. A. Puretzky , R. Torsi , C. Liu , I. N. Ivanov , G. Duscher , D. B. Geohegan , Z. Ni , K. Xiao , and H. Zhao , Excitonic dynamics in janus MoSSe and WSSe monolayers, Nano Lett. 21(2), 931 (2021)

[19] C. Liu , T. Liang , X. Sui , L. Du , Q. Guo , G. Xue , C. Huang , Y. You , G. Yao , M. Zhao , J. Yin , Z. Sun , H. Hong , E. Wang , and K. Liu , Anomalous photovoltaics in Janus MoSSe monolayers, Nat. Commun. 16(1), 544 (2025)

[20] Y. Wang , R. Chen , X. Luo , Q. Liang , Y. Wang , and Q. Xie , First-principles calculations on Janus MoSSe/graphene van der Waals heterostructures: Implications for electronic devices, ACS Appl. Nano Mater. 5(6), 8371 (2022)

[21] C. Long , Y. Dai , Z. R. Gong , and H. Jin , Robust type-II band alignment in Janus-MoSSe bilayer with extremely long carrier lifetime induced by the intrinsic electric field, Phys. Rev. B 99(11), 115316 (2019)

[22] Y. Hou , Y. Wang , L. Yin , Y. Wen , X. Hou , R. Cheng , and J. He , Metal-insulator transition in an isoelectronically doped transition metal dichalcogenide and its heterostructures, Front. Phys. (Beijing) 20(4), 044209 (2025)

[23] R. Li , Z. Shi , R. Xiong , Z. Cui , Y. Zhang , C. Xu , J. Zheng , B. Wu , B. Sa , and C. Wen , Computational mining of GeH-based Janus III-VI van der Waals heterostructures for solar cell applications, Phys. Chem. Chem. Phys. 25(9), 6674 (2023)

[24] J. Yuan , F. Wang , Z. Zhang , B. Song , S. Yan , M. H. Shang , C. Tong , and J. Zhou , Effects of electric field and interlayer coupling on Schottky barrier of germanene/MoSSe vertical heterojunction, Phys. Rev. B 108(12), 125404 (2023)

[25] X. Jiang,W. Xie,X. Xu,Q. Gao,D. Li,B. Cui,D. Liu,F. Qu, A bifunctional GeC/SnSSe heterostructure for highly efficient photocatalysts and photovoltaic devices, Nanoscale 14(19), 7292 (2022)

[26] G. L. Qian , Q. Xie , Q. Liang , X. Y. Luo , and Y. X. Wang , Electronic properties and photocatalytic water splitting with high solar-to-hydrogen efficiency in a hBNC/Janus WSSe heterojunction: First-principles calculations, Phys. Rev. B 107(15), 155306 (2023)

[27] C. Lu , S. Zhang , M. Chen , H. Chen , M. Zhu , Z. Zhang , J. He , L. Zhang , and X. Yuan , Van der Waals epitaxy of type-II band alignment CsPbI₃/TMDC heterostructure for optoelectronic applications, Front. Phys. (Beijing) 19(5), 53206 (2024)

[28] K. S. Novoselov , Dual single-site catalyst promoter boosts catalytic performance, Natl. Sci. Rev. 7(12), 1841 (2020)

[29] G. F. Kresse and J. Furthmüller and J , Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set, Phys. Rev. B 54(16), 11169 (1996)

[30] M. K. Mohanta , A. Arora , A. De Sarkar , and Effective modulation of ohmic contact and carrier concentration in a graphene-MgX (X= S , Se) van der Waals heterojunction with tunable band-gap opening via strain and electric field, Phys. Rev. B 104(16), 165421 (2021)

[31] J. Heyd , G. E. Scuseria , and M. Ernzerhof , Hybrid functionals based on a screened Coulomb potential, J. Chem. Phys. 118(18), 8207 (2003)

[32] H. J. Monkhorst and J. D. Pack , Special points for Brillouin-zone integrations, Phys. Rev. B 13(12), 5188 (1976)

[33] B. Zhou , A. Cui , L. Gao , K. Jiang , L. Shang , J. Zhang , Y. Li , S. J. Gong , Z. Hu , and J. Chu , Enhancement effects of interlayer orbital hybridization in Janus MoSSe and tellurene heterostructures for photovoltaic applications, Phys. Rev. Mater. 5(12), 125404 (2021)

[34] S. Smidstrup,T. Markussen,P. Vancraeyveld,J. Wellendorff,J. Schneider,T. Gunst,B. Verstichel,D. Stradi,P. A. Khomyakov,U. G. Vej-Hansen,M. E. Lee,S. T. Chill,F. Rasmussen,G. Penazzi,F. Corsetti,A. Ojanpera,K. Jensen,M. L. N. Palsgaard,U. Martinez,A. Blom,M. Brandbyge,K. Stokbro,A. T. K. Quantum, an integrated platform of electronic and atomic-scale modelling tools, J. Phys. Condens. Matter 32(1), 015901 (2020)

[35] M. Yagmurcukardes and F. M. Peeters , Stable single layer of Janus MoSO: Strong out-of-plane piezoelectricity, Phys. Rev. B 101(15), 155205 (2020)

[36] A. Ali , J. M. Zhang , I. Muhammad , I. Shahid , Y. H. Huang , X. M. Wei , and F. Kabir , Theoretical perspective on the electronic structure and optoelectronic properties of type-II SiC/CrS₂ van der Waals heterostructure with high carrier mobilities, J. Phys.: Condens. Matter 33(21), 215302 (2021)

[37] R. X. Li , X. L. Tian , S. C. Zhu , Q. H. Mao , J. Ding , and H. D. Li , MoSi₂N₄/CrS₂ van der Waals heterostructure with high solar-to-hydrogen efficiency, Physica E 144, 115443 (2022)

[38] S. B. Sharma , R. Paudel , R. Adhikari , G. C. Kaphle , D. Paudyal , and Structural deformation and mechanical response of CrS₂ , CrSe₂ and Janus CrSSe, Physica E 146, 115517 (2023)

[39] K. Zhang , Y. Guo , Q. Ji , A. Y. Lu , C. Su , H. Wang , A. A. Puretzky , D. B. Geohegan , X. Qian , S. Fang , E. Kaxiras , J. Kong , and S. Huang , Enhancement of van der Waals interlayer coupling through polar Janus MoSSe, J. Am. Chem. Soc. 142(41), 17499 (2020)

[40] X. Li , T. Liu , L. Li , M. He , C. Shen , J. Li , and C. Xia , Reconfigurable band alignment of m-GaS/n-XTe₂ (X = Mo, W) multilayer van der Waals heterostructures for photoelectric applications, Phys. Rev. B 106(12), 125306 (2022)

[41] Z. Zhou , X. Niu , Y. Zhang , and J. Wang , Janus MoSSe/WSeTe heterostructures: A direct Z-scheme photocatalyst for hydrogen evolution, J. Mater. Chem. A 7(38), 21835 (2019)

[42] S. Li , K. Wei , Q. Liu , Y. Tang , and T. Jiang , Twistronics and moiré excitonic physics in van der Waals heterostructures, Front. Phys. (Beijing) 19(4), 42501 (2024)

[43] X. Zeng , C. Wan , Z. Zhao , D. Huang , Z. Wang , X. Cheng , and T. Jiang , Nonlinear optics of two-dimensional heterostructures, Front. Phys. (Beijing) 19(3), 33301 (2023)

[44] X. Ma , S. Fu , J. Ding , M. Liu , A. Bian , F. Hong , J. Sun , X. Zhang , X. Yu , and D. He , Robust interlayer exciton in WS₂/MoSe₂ van der Waals heterostructure under high pressure, Nano Lett. 21(19), 8035 (2021)

[45] C. Q. Nguyen , Y. S. Ang , S. T. Nguyen , N. V. Hoang , N. M. Hung , and C. V. Nguyen , Tunable type-II band alignment and electronic structure of C₃N₄/MoSi₂N₄ heterostructure: Interlayer coupling and electric field, Phys. Rev. B 105(4), 045303 (2022)

[46] E. Vessally , M. Vali , A. Hosseinian , M. R. Poor Heravi , and A. Bekhradnia , Mustard gas adsorption on the pristine and BN-doped graphynes: A computational study, Phys. Lett. A 384(21), 126479 (2020)

[47] L. Li , P. Yuan , T. Liu , Z. Ma , C. Xia , and X. Li , Self-powered broadband photodetector based on a monolayer InSe p-i-n homojunction, Phys. Rev. Appl. 19(1), 014039 (2023)

[48] S. Jia , Z. Jin , J. Zhang , J. Yuan , W. Chen , W. Feng , P. Hu , P. M. Ajayan , and J. Lou , Lateral monolayer MoSe₂-WSe₂ p-n heterojunctions with giant built-in potentials, Small 16(34), 2002263 (2020)

[49] M. M. Furchi , A. Pospischil , F. Libisch , J. Burgdörfer , and T. Mueller , Photovoltaic effect in an electrically tunable van der Waals heterojunction, Nano Lett. 14(8), 4785 (2014)

[50] M. S. Long , A. Y. Gao , P. Wang , H. Xia , C. Ott , C. Pan , Y. J. Fu , E. F. Liu , X. S. Chen , W. Lu , T. Nilges , J. B. Xu , X. Wang , W. Hu , and F. Miao , Room temperature high-detectivity mid-infrared photodetectors based on black arsenic phosphorus, Sci. Adv. 3(6), e1700589 (2017)

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