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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