Two-dimensional molybdenum disulfide (MoS2) has emerged as a promising material for optoelectronic applications because of its superior electrical and optical properties. However, the difficulty in synthesizing large-scale MoS2 films has been recognized as a bottleneck in uniform and reproducible device fabrication and performance. Here, we proposed a radio-frequency magnetron sputter system, and post-treatments of electron beam irradiation and sulfurization to obtain large-scale continuous and high-quality multilayer MoS2 films. Large-area uniformity was confirmed by no deviation of electrical performance in fabricated MoS2 thin-film transistors (TFTs) with an average on/off ratio of 103 and a transconductance of 0.67 nS. Especially, the photoresponsivity of our MoS2 TFT reached 3.7 A W–1, which is a dramatic improvement over that of a previously reported multilayer MoS2 TFT (0.1 A W–1) because of the photogating effect induced by the formation of trap states in the band gap. Finally, we organized a 4 × 4 MoS2 phototransistor array with high photosensitivity, linearity, and uniformity for light detection, which demonstrates the great potential of 2D MoS2 for future-oriented optoelectronic devices.

We synthesised a crystalline MoS2 film from as-sputtered amorphous film by applying an electron beam irradiation (EBI) process. A collimated electron beam (60 mm dia.) with an energy of 1 kV was irradiated for only 1 min to achieve crystallisation without an additional heating process. After the EBI process, we observed a two-dimensional layered structure of MoS2 about 4 nm thick and with a hexagonal atomic arrangement on the surface. A stoichiometric MoS2 film was confirmed to grow well on SiO2/Si substrates and include partial oxidation of Mo. In our experimental configuration, EBI on an atomically thin MoS2 layer stimulated the transformation from a thermodynamically unstable amorphous structure to a stable crystalline nature with a nanometer grain size. We employed a Monte Carlo simulation to calculate the penetration depth of electrons into the MoS2 film and investigated the atomic rearrangement of the amorphous MoS2 structure.

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WS2-based photodetectors were fabricated by sputtering and electron beam irradiation (EBI), and the effect of EBI on the crystallization of WS2 films was investigated. EBI at 1 kV energy for 1 min transformed the as-deposited amorphous structure of WS2 film into a two-dimensional (2D) layered crystalline structure with high uniformity over a 50.8 mm diameter wafer. Additionally, EBI enhanced the photoelectrical properties of WS2-based photodetectors. The as-deposited WS2 film yielded a responsivity of 0.10 mA · W−1 under 450 nm laser irradiation, but showed no response under 532 and 635 nm laser wavelengths. However, after 1 kV and 3 kV EBI of the WS2 films, the responsivities under laser irradiation at 450, 532, and 635 nm were 0.36, 1.37, and 0.19 mA · W−1, and 1.68, 2.45, and 1.09 mA · W−1, respectively. The substrate temperatures after 1 min of 1 kV and 3 kV EBI were 102 °C and 591 °C, respectively. The WS2-based photodetectors exhibited high responsivity in the visible light region despite their unique process conditions of low temperature and fast EBI treatment. Such desirable performance of the EBI-treated WS2 films shows significant potential for future large-area and low-temperature photoelectronic applications. Thus, we demonstrated that EBI is an attractive method for synthesizing 2D materials as it is fast, simple, controllable, and compatible with sputtering processes.

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We herein aim to improve the understanding of the photoresponsive behavior of electron-beam irradiated MoS2 films. In this context, MoS2-based photodetectors were fabricated via sputtering and electron beam irradiation (EBI). The structural transformation imparted on MoS2 through EBI and the relationship between the structural, stoichiometric, and photoelectric properties of the synthesized MoS2 were investigated. MoS2 channels displayed a remarkable photoresponse in the visible light region. More specifically, MoS2 treated with 3 kV-EBI showed a responsivity of 7.61 mA/W when illuminated by a 450 nm laser, which is a 970% increase from that of the as-deposited MoS2. The variation of the time-dependent photocurrent with respect to the EBI parameters employed was attributed to the internal defects of MoS2. We concluded that EBI is a low-temperature process that is compatible with sputtering, and it exhibits potential for application in the area of flexible optoelectronics.

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