Transfer-free, scalable vertical heterostructure FET on MoS₂/WS₂ continuous films

Abstract

Taking into account the novel layered structure and unusual electronic properties of MoS2 and WS2 on the side the lack of dangling bonds between these two components and donor-acceptor linkage effects, growth of the MoS2/WS2 vertical heterojunction film on the amorphous SiO2/Si substrate have created high demand. In this study, we reported the continuous, scalable, and vertical MoS2/WS2 heterostructure film by using a sputtering without a transfer step. The WS2 film was continuously grown on MoS2 and eventually led to the formation of the MoS2/WS2 vertical heterojunction film. Dozens of FETs fabricated on MoS2/WS2 continuous heterojunction film were created on the same substrate in a single lithographic fabrication step, allowing them to be commercialized and not only used in research applications. RAMAN spectra proved the formation of the MoS2/WS2 heterostructure film. In XPS measurements, it was shown that a separate MoS2 and WS2 layer was grown instead of the alloy structure. The polarity behavior of the MoS2/WS2 heterostructure FET was found to be modulated with different drain voltages as p-type to ambipolar and finally n-type conductivity because of the transition of band structure and Schottky barrier heights at different drain voltages. Electron mobility (7.2 cm2/V.s) and on/off ratio (104-105) exhibited by the MoS2/WS2 heterostructure FETs displayed a more improved electrical performance than that of individual WS2, MoS2 devices. It was observed that the mobility value of MoS2/WS2 FET was approximately 514 times greater than WS2 FET and 800 times greater than MoS2 FET. Additionally, the MoS2/WS2 FET on/off ratio was larger than 2 order MoS2 FET and 1 order WS2 FET. The film of continuous vertical heterojunctions as in the MoS2/WS2 currents in the study would be a promising candidate for nanoelectronics fields. This work demonstrated the progress towards realizing carrier-type controlled high-performance MoS2/WS2 heterojunction-based FETs for future logic devices.

Large area van der Waals MoS2–WS2 heterostructures for visible-light energy conversion

“…61 and in more recent references. 27,[62][63][64][65][66][67][68] We also stress that the absolute photocurrent and photovoltage values which have been measured in our proofof-concept TMD heterojunction are far too low for any realistic electro-optical photoconversion application. This limitation is primarily due to the very high series resistance of the graphene bilayer back contact, in the range of 20 kΩ (more details in ESI † section S4).…”

Recent progress on ambipolar 2D semiconductors in emergent reconfigurable electronics and optoelectronics

“…[167] Vertical van der Waals heterostructures combined with ambipolar 2D semiconductors allow for the integration of highly disparate materials with crystal lattice mismatching. [168] They have been employed in the construction of high-performance electronic and optoelectronic devices, such as ReSe 2 /MoS 2 van der Waals heterostructures, which exhibit ultra-fast and linear polarization-sensitive photodetectors, [169] vertical MoS 2 /WS 2 heterostructure with ambipolarity behavior, [170] vertical graphene/WS 2 /graphene van der Waals heterostructure with a low off-state current and a high ON/OFF ratio, exhibiting both n-type and bipolartype conduction, [171] ReSe 2 /PtSe 2 heterojunction for highperformance photodetectors, [172] WSe 2 /InSe heterostructure photodetector with ambipolar photoresponsivity, [173] and ambipolar SnO/SnS heterojunction transistors employed to build CMOS inverters. [174] Such investigations indicate that vertical heterostructures hold great potential for use in reconfigurable devices towards high-performance integrated circuits and systems.…”

High-Performance 1D–2D Te/MoS2 Heterostructure Photodetectors with Tunable Giant Persistent Photoconductivity

“…Two-dimensional (2D) semiconducting materials have been studied extensively as photodetectors because of their intriguing optical properties. − Among them, transition metal dichalcogenides (TMDCs) are one of the most investigated owing to their widely tunable electronic bandgap ranging from ∼few tens meV to ∼2 eV. − Even though various studies have reported the wafer-scale synthesis of TMDCs for CMOS-based applications, − TMDCs are vulnerable to oxidation from ambient conditions, which have impeded their use as a replacement for Si technology. In the past few years, air-stable layered materials, such as n-type bismuth oxychalcogenides (Bi 2 O 2 Se), and monoelemental materials, such as p-type tellurene, have been synthesized by chemical vapor deposition (CVD) and hydrothermal synthesis − and utilized for short wavelength infrared (SWIR) photodetectors and MIR at room temperature. − Since photodetectors integrated with single 2D materials in the conventional transistor configuration exhibit very low photoresponses owing to their very small absorption cross section and only the interface of the gate (G)–source (S) and gate (G)–drain (D) contributing to the photocurrent induced by electron and hole separation at the Schottky barrier, vertically stacked photoreactors have been investigated to overcome this issue by maximizing photoactive area, i.e., highly enhanced absorption cross section. − Among them, a vertically stacked van der Waals heterojunction, i.e., forming a p–n junction using two different kinds of materials, or the same type of polarity with different Fermi level has been reported for a high on/off ratio, − superior interface quality because of the lack of dangling bonds in the 2D materials, − and bandgap engineering due to numerous selections of van der Waals materials of various bandgaps and work function for p- and n-type semiconductors. , These devices usually exhibit a photoresponse toward fast photodetectors with rise or fall times of tens of μs to ms. ,− Even though a very slow photoresponse with a long retention time in vertically stacked heterostructured devices using van der Waals 2D materials has been recently reported, − …”