Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted considerable attention owing to their synergetic effects with other 2D materials, such as graphene and hexagonal boron nitride, in TMD-based heterostructures. Therefore, it is important to understand the physical properties of TMD–TMD vertical heterostructures for their applications in next-generation electronic devices. However, the conventional synthesis process of TMD–TMD heterostructures has some critical limitations, such as nonreproducibility and low yield. In this paper, we synthesize wafer-scale MoS2–WS2 vertical heterostructures (MWVHs) using plasma-enhanced chemical vapor deposition (PE-CVD) via penetrative single-step sulfurization discovered by time-dependent analysis. This method is available for fabricating uniform large-area vertical heterostructures (4 in.) at a low temperature (300 °C). MWVHs were characterized using various spectroscopic and microscopic techniques, which revealed their uniform nanoscale polycrystallinity and the presence of vertical layers of MoS2 and WS2. In addition, wafer-scale MWVHs diodes were fabricated and demonstrated uniform performance by current mapping. Furthermore, mode I fracture tests were performed using large double cantilever beam specimens to confirm the separation of the MWVHs from the SiO2/Si substrate. Therefore, this study proposes a synthesis mechanism for TMD–TMD heterostructures and provides a fundamental understanding of the interfacial properties of TMD–TMD vertical heterostructures.
The specific capacitance values describe the effect of urea concentration for nitrogen-doped molybdenum sulphide.
The conventional synthesis of two-dimensional (2D) transition metal dichalcogenide (TMDC) heterostructures is low yielding and lack the heterojunction interface quality. The chemical vapor deposition (CVD) techniques have achieved highquality heterostructure interfaces but require a high synthesis temperature (>600 °C) and have a low yield of heterostructures. Therefore, the large scale and high interface quality of TMDC heterojunctions using low-temperature synthesis methods are in demand. Here, high-quality, wafer-scale MoS 2 and WS 2 heterostructures with 2D interfaces were prepared by a one-step sulfurization of the molybdenum (Mo) and tungsten (W) precursors via plasma-enhanced CVD at a relatively low temperature (150 °C). The 4 inch wafer-scale synthesis of the MoS 2 −WS 2 heterostructures was validated using various spectroscopic and microscopic techniques. Further, the photocurrent generation and photoswitching phenomenon of the so-obtained MoS 2 −WS 2 heterostructures were studied. The photodevice prepared by the MoS 2 −WS 2 heterostructures at 150 °C showed a photoresponsivity of 83.75 mA/W. The excellent photoresponse and faster photoswitching highlight the advantage of MoS 2 −WS 2 heterostructures toward advanced photodetectors.
Two-dimensional molybdenum disulfide (MoS2) is one of the most promising candidates for next-generation semiconductors. Among the advantages offered by MoS2, a tunable bandgap that depends on the thickness is essential for the on-demand manufacturing of nanoelectronics. For this reason, elaborate layer control of MoS2 has been a long-standing research objective. However, prior efforts had several critical issues including surface roughness, poor uniformity/scalability, and impurities. Through this study, we aimed to achieve both ultrahigh precision and purity in large-scale (4 in.) layer control of MoS2 by two consecutive plasma processes: plasma-enhanced chemical vapor deposition (PECVD) and reactive ion etching (RIE). The 4 in. wafer-scale MoS2 was synthesized by PECVD, and the as-grown bulk layers were etched using RIE with a computationally screened gas mixture in the cyclic step. For every RIE cycle, the 4 in. MoS2 wafer was evenly etched to a thickness of 0.3–0.4 nm while there was no damage to the atomic structure and chemical impurities. For the computational screening of candidate gases, first-principles calculations explored the energetics of surface reaction and offered physical insights into the associated electronic interaction. The combination of computational screening and experimentation accelerates optimal process design and provides an in-depth understanding of the plasma–surface interactions.
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