Authors: Lu Li | Y. Q. Zhang | Dongxia Shi | Guangyu Zhang
Source: Acta Physica Sinica (article, 2022-01-01)
Field: Materials Science — Materials Chemistry

Cotrollable growth of monolayer MoS&lt;sub&gt;2&lt;/sub&gt; films and their applications in devices Monolayer molybdenum disulfide (MoS&lt;sub&gt;2&lt;/sub&gt;) is an emerging two-dimensional (2D) semiconductor material.The MoS&lt;sub&gt;2&lt;/sub&gt; film has a natural atomic-level thickness, excellent optoelectronic and mechanical properties, and it also has the potential applications in very large-scale integration technology in the future. In this article we summarize the research progress made by our group in the studying of monolayer MoS&lt;sub&gt;2&lt;/sub&gt; films in the past few years. The controlled growth of large-size MoS&lt;sub&gt;2&lt;/sub&gt; single crystals is achieved by oxygen-assisted chemical vapor deposition method. By a unique facile multisource CVD growth method, the highly oriented and large domain size ML MoS&lt;sub&gt;2&lt;/sub&gt; films are epitaxially grown on a 4-inch wafer scale. Almost only 0° and 60° oriented domains are present in films, and the average size of MoS&lt;sub&gt;2&lt;/sub&gt; grains ranges from 100 μm to 180 μm . The samples exhibit their best optical and electrical quality ever obtained, as evidenced from their wafer-scale homogeneity, nearly perfect lattice structure, average room-temperature device mobility of ~70 cm&lt;sup&gt;2&lt;/sup&gt;·V&lt;sup&gt;–1&lt;/sup&gt;·s&lt;sup&gt;–1&lt;/sup&gt; and high on/off ratio of ~10&lt;sup&gt;9&lt;/sup&gt; on SiO&lt;sub&gt;2&lt;/sub&gt; substrates. By adjusting the oxygen doping concentration in the MoS&lt;sub&gt;2&lt;/sub&gt; film through using an effective CVD technique, electrical and optical properties can be well modified, thereby greatly improving the carrier mobilities and controllable n-type electronic doping effects resulting from optimized oxygen doping levels of MoS&lt;sub&gt;2–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;O&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; . In terms of MoS&lt;sub&gt;2&lt;/sub&gt; thin film devices and applications, the 4-inch wafer-scale high-quality MoS&lt;sub&gt;2&lt;/sub&gt; monolayers are used to fabricate the transparent MoS&lt;sub&gt;2&lt;/sub&gt;-based transistors and logic circuits on flexible substrates. This large-area flexible FET device shows excellent electrical performance with a high device density (1,518 transistors per cm&lt;sup&gt;2&lt;/sup&gt;) and yield (97%), and exhibits a high on/off ratio (10&lt;sup&gt;10&lt;/sup&gt;), current density (~35 μA·μm&lt;sup&gt;–1&lt;/sup&gt;), mobility (~55 cm&lt;sup&gt;2&lt;/sup&gt;·V&lt;sup&gt;–1&lt;/sup&gt;·s&lt;sup&gt;–1&lt;/sup&gt;) and flexibility. Based on the vertically integrated multilayer device via a layer-by-layer stacking process, an individual layer of all-2D multifunctional FET is successfully achieved with nearly multiplied on-current density, equivalent device mobility, and persevered on/off ratio and subthreshold swing (SS) of the individual layer, the combined performance of the device is fully utilized, and the integration of “sensing-storing-computing” is realized. A two-terminal floating-gate memory (2TFGM) based artificial synapse built from all-2D van der Waals materials is prepared, the 2TFGM synaptic device exhibits excellent linear and symmetric weight update characteristics with high reliability and tunability. A large number of states of up to ≈3000, high switching speed of 40 ns and low energy consumption of 18 fJ for a single pulse are demonstrated experimentally. The introduction of structural domain boundaries in the basal plane of monolayer MoS&lt;sub&gt;2&lt;/sub&gt; can greatly enhance its hydrogen evolution reaction performance by serving as active sites. The progress we have made in the preparation of monolayer MoS&lt;sub&gt;2&lt;/sub&gt; films and the research on device characteristics is of guiding significance for the basic and application research of MoS&lt;sub&gt;2&lt;/sub&gt;, and also is universal and instructive for other 2D transition metal dichalcogenides. Monolayer ; Materials science ; Chemical vapor deposition ; Epitaxy ; Molybdenum disulfide ; Nanotechnology ; Wafer ; Crystallography ; Analytical Chemistry (journal) ; Chemistry ; Layer (electronics) ; Metallurgy 2D Materials and Applications ; Advanced Sensor and Energy Harvesting Materials ; Nanowire Synthesis and Applications