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First principles calculation was performed to study the Sn 2 Te 2 X 4 (X = P, As) monolayers. Structural investigation confirms the stability of the two monolayers with Young's modulus in the range of 30.34-33.65 N m -1 and a Poisson's ratio of 0.18-0.21. The two monolayers are semiconductors with a direct band gap of 1.52-1.66 eV. The light absorption rate of the two monolayers is rather high 10 4 -10 5 cm -1 . Both monolayers have high charge carrier mobility and suitable VBM and CBM positions for the redox reaction. The η STH efficiency of both materials (15.76-17.12%) is close to the theoretical limit of 18%. Moreover, moderate strains can improve the light absorption rate, while the suitable VBM and CBM positions are preserved. These characteristics suggest that Sn 2 Te 2 X 4 (X = P, As) monolayers are good candidates for being applied in flexible devices and for the conversion of solar energy to other types of energy., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

Minimizing the contact barriers at the interface, forming between two different two-dimensional metals and semiconductors, is essential for designing high-performance optoelectronic devices. In this work, we design different types of metal-semiconductor heterostructures by combining 2D metallic MX 2 (M = Nb, Hf; X = S, Se) and 2D semiconductor SiH and investigate systematically their electronic properties and contact characteristics using first principles calculations. We find that all the MX 2 /SiH (M = Nb, Ta; X = S, Se) heterostructures are energetically stable, suggesting that they could potentially be synthesized in the future. Furthermore, the generation of the MX 2 /SiH metal-semiconductor heterostructures leads to the formation of the Schottky contact with ultra-low Schottky barriers of a few tens of meV. This finding suggests that all the 2D MX 2 (M = Nb, Ta; X = S, Se) metals act as effective electrical contact 2D materials to contact with the SiH semiconductor, enabling electronic devices with high charge injection efficiency. Furthermore, the tunneling resistivity of all the MX 2 /SiH (M = Nb, Ta; X = S, Se) MSHs is low, confirming that they exhibit high electron injection efficiency. Our findings underscore fundamental insights for the design of high-performance multifunctional Schottky devices based on the metal-semiconductor MX 2 /SiH heterostructures with ultra-low contact barriers and high electron injection efficiency., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Breaking structural symmetry in two-dimensional layered Janus materials can result in enhanced new phenomena and create additional degrees of piezoelectric responses. In this study, we theoretically design a series of Janus monolayers HfGeZ 3 H (Z = N, P, As) and investigate their structural characteristics, crystal stability, piezoelectric responses, electronic features, and carrier mobility using first-principles calculations. Phonon dispersion analysis confirms that HfGeZ 3 H monolayers are dynamically stable and their mechanical stability is also confirmed through the Born-Huang criteria. It is demonstrated that while HfGeN 3 H is a semiconductor with a large bandgap of 3.50 eV, HfGeP 3 H and HfGeAs 3 H monolayers have narrower bandgaps being 1.07 and 0.92 eV, respectively. When the spin-orbit coupling is included, large spin-splitting energy is found in the electronic bands of HfGeZ 3 H. Janus HfGeZ 3 H monolayers can be treated as piezoelectric semiconductors with the coexistence of both in-plane and out-of-plane piezoelectric responses. In particular, HfGeZ 3 H monolayers exhibit ultra-high electron mobilities up to 6.40 × 10 3 cm 2 V -1 s -1 (HfGeAs 3 H), indicating that they have potential for various applications in nanoelectronics., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

The emergence of van der Waals (vdW) heterostructures, which consist of vertically stacked two-dimensional (2D) materials held together by weak vdW interactions, has introduced an innovative avenue for tailoring nanoelectronic devices. In this study, we have theoretically designed a metal/semiconductor heterostructure composed of NbS 2 and Janus MoSSe, and conducted a thorough investigation of its electronic properties and the formation of contact barriers through first-principles calculations. The effects of stacking configurations and the influence of external electric fields in enhancing the tunability of the NbS 2 /Janus MoSSe heterostructure are also explored. Our findings demonstrate that the NbS 2 /MoSSe heterostructure is not only structurally and thermally stable but also exfoliable, making it a promising candidate for experimental realization. In its ground state, this heterostructure exhibits p-type Schottky contacts characterized by small Schottky barriers and low tunneling barrier resistance, showing its considerable potential for utilization in electronic devices. Additionally, our findings reveal that the electronic properties, contact barriers and contact types of the NbS 2 /MoSSe heterostructure can be tuned by applying electric fields. A negative electric field leads to a conversion from a p-type Schottky contact to an n-type Schottky contact, whereas a positive electric field gives rise to a transformation from a Schottky into an ohmic contact. These insights offer valuable theoretical guidance for the practical utilization of the NbS 2 /MoSSe heterostructure in the development of next-generation electronic and optoelectronic devices., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

From the extending requirements for using innovative materials in advanced technologies, it is necessary to explore new materials for relevant applications. In this work, we design new two-dimensional (2D) Janus ZrSiSZ 2 (Z = N, P, As) monolayers and investigate their crystal lattice and dynamic stability by using density functional theory investigations. The two stable structures of ZrSiSP 2 and ZrSiSAs 2 are then systematically examined for thermal, energetic, and mechanical stability, and electronic and transport properties. The calculation results demonstrate that both the ZrSiSP 2 and ZrSiSAs 2 monolayers have good thermal stability at room temperature and high energetic/mechanical stabilities for experimental synthesis. The studied structures are found to be in-direct semiconductors. Specifically, with moderate band-gap energies of 1.04 to 1.29 eV for visible light absorption, ZrSiSP 2 and ZrSiSAs 2 can be considered potential candidates for photovoltaic applications. The applied biaxial strains and external electric fields slightly change the band-gap energies of the monolayers. We also calculate the carrier mobilities for the transport properties based on the deformation potential method. Due to the lower effective masses, the carrier mobilities in the x direction are higher than those in the y direction. The carrier mobilities of the ZrSiSP 2 and ZrSiSAs 2 monolayers are anisotropic not only in transport directions but also for the electrons and holes. We believe that the results of our work may stimulate further studies to explore more new 2D Janus monolayers with novel properties of the MA 2 Z 4 family materials., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

Two-dimensional (2D) metal-semiconductor heterostructures play a critical role in the development of modern electronics technology, offering a platform for tailored electronic behavior and enhanced device performance. Herein, we construct a novel 2D metal-semiconductor MoSH@MoS 2 heterostructure and investigate its structures, electronic properties and contact characteristics using first-principles investigations. We find that the MoSH@MoS 2 heterostructure exhibits a p-type Schottky contact, where the specific Schottky barrier height varies depending on the stacking configurations employed. Furthermore, the MoSH@MoS 2 heterostructures possess low tunneling probabilities, indicating a relatively low electron transparency across all the patterns of the MoSH@MoS 2 heterostructures. Interestingly, by modulating the electric field, it is possible to modify the Schottky barriers and achieve a transformation from a p-type Schottky contact into an n-type Schottky contact. Our findings pave the way for the development of advanced electronics technology based on metal-semiconductor MoSH@MoS 2 heterostructures with enhanced tunability and versatility., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

In this work, we propose novel two-dimensional Janus XCrSiN 2 (X = S, Se, and Te) single-layers and comprehensively investigate their crystal structure, electronic properties, and carrier mobility by using a first-principles method. These configurations are the combination of the CrSi 2 N 4 material and a transition metal dichalcogenide. The X-Cr-SiN 2 single-layers are constructed by replacing the N-Si-N atomic layer on one side with chalcogen atoms (S, Se, or Te). The structural characteristics, mechanical or thermal stabilities, and electronic properties are investigated adequately. All three examined configurations are energetically stable and are all small-bandgap semiconductors (<1 eV). Since the mirror symmetry is broken in the Janus material, there exists a remarkable built-in electric field and intrinsic dipole moment. Therefore, the spin-orbit interaction is considered intensively. However, it is observed that the spin-orbit coupling has insignificant effects on the electronic properties of XCrSiN 2 (X = S, Se, and Te). Moreover, an external electric field and strain are applied to evaluate the adjustment of the electronic features of the three structures. The transport properties of the proposed configurations are calculated and analyzed systematically, indicating the highly directional isotropy. Our results suggest that the proposed Janus XCrSiN 2 could be potential candidates for various applications, especially in nanoscale electronic devices., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)