Controlled Growth of a Large-Size 2D Selenium Nanosheet and Its Electronic and Optoelectronic Applications

Abstract: Selenium has attracted intensive attention as a promising material candidate for future optoelectronic applications. However, selenium has a strong tendency to grow into nanowire forms due to its anisotropic atomic structure, which has largely hindered the exploration of its potential applications. In this work, using a physical vapor deposition method, we have demonstrated the synthesis of large-size, high-quality 2D selenium nanosheets, the minimum thickness of which could be as thin as 5 nm. The Se nanosheet exhibits a strong in-plane anisotropic property, which is determined by angle-resolved Raman spectroscopy. Back-gating field-effect transistors based on a Se nanosheet exhibit p-type transport behaviors with on-state current density around 20 mA/mm at Vds = 3 V. Four-terminal field effect devices are also fabricated to evaluate the intrinsic hole mobility of the selenium nanosheet, and the value is determined to be 0.26 cm2 Vs at 300 K. The selenium nanosheet phototransistors show an excellent photoresponsivity of up to 263 A/W, with a rise time of 0.1 s and fall time of 0.12 s. These results suggest that crystal selenium as a 2D form of a 1D van der Waals solid opens up the possibility to explore device applications.

Synthesis and Applications of Large-Size 2D Selenium Nanosheets

The research presented in the paper explores the controlled growth of large-size two-dimensional (2D) selenium (Se) nanosheets through a physical vapor deposition (PVD) method and their promising applications in electronics and optoelectronics. The study addresses the inherent challenges of selenium's anisotropic crystal structure, which predisposes it to form one-dimensional (1D) nanostructures. By developing a vapor-phase technique, the authors achieve high-quality 2D Se nanosheets with a minimum thickness of 5 nm, providing a new avenue for assessing selenium's properties and potential applications.

Key Findings

1. Synthesis Method and Structural Properties: The PVD method successfully synthesized Se nanosheets with dimensions up to 50 μm in length and 8 μm in width. The nanosheets exhibit distinct zigzag edge structures and demonstrate in-plane anisotropic properties confirmed via angle-resolved Raman spectroscopy. Transmission electron microscopy (TEM) suggests an oriented growth along the <1210> direction, distinct from typical bulk Se behavior.

2. Electronic Properties: The study constructs back-gated field-effect transistors (FETs) using the Se nanosheets, which show p-type transport with an on-state current density of approximately 20 mA/mm at a gate voltage of 3V. The intrinsic hole mobility was calculated to be 0.26 cm²/V·s at room temperature, which is similar to those found in bulk selenium and selenium nanobelts.

3. Optoelectronic Performance: Phototransistors fabricated from the Se nanosheets exhibited remarkable photoresponsivity, achieving 263 A/W with a rise time of 0.10 s and a fall time of 0.12 s. This photoresponsivity is significantly higher than that reported for other 2D materials, indicating Se nanosheets' suitability for high-sensitivity photoelectric applications.

Implications and Future Directions

The successful synthesis of Se in a 2D nanosheet form offers substantial implications for both theoretical studies and practical applications. The anisotropic properties and elevated photoresponsivity suggest potential in next-generation optoelectronic devices, including sensors and photovoltaic systems. The study provides a foundation for further refinement in producing 2D materials from 1D van der Waals materials.

Future research can expand on the methods used for semiconductor integration and the improvement of charge transport properties. Additionally, exploring the interaction of these Se nanosheets in heterostructures with other 2D materials could lead to innovative device applications. The environmental stability of these materials, as evidenced by their stability over time, further supports their use in real-world applications and long-term device performance.

Conclusion

This paper contributes to the growing interest in novel 2D materials by presenting a robust methodology for synthesizing large-area Se nanosheets with excellent electronic and optoelectronic properties. The work opens a pathway for leveraging the unique characteristics of selenium for advanced device applications, reinforcing the role of 2D materials in future technologies. Thus, while challenges in scalability and material integration remain, this study underscores the potential utility of 2D selenium in broad scientific and commercial contexts.