High-Crystalline\nMonolayer Transition Metal Dichalcogenides\nFilms for Wafer-Scale Electronics

Abstract

Chemical\nvapor deposition (CVD) using liquid-phase precursors has\nemerged as a viable technique for synthesizing uniform large-area\ntransition metal dichalcogenide (TMD) thin films. However, the liquid-phase\nprecursor-assisted growth process typically suffers from small-sized\ngrains and unreacted transition metal precursor remainders, resulting\nin lower-quality TMDs. Moreover, synthesizing large-area TMD films\nwith a monolayer thickness is also quite challenging. Herein, we successfully\nsynthesized high-quality large-area monolayer molybdenum diselenide\n(MoSe₂) with good uniformity via promoter-assisted liquid-phase\nCVD process using the transition metal-containing precursor homogeneously\nmodified with an alkali metal halide. The formation of a reactive\ntransition metal oxyhalide and reduction of the energy barrier of\nchalcogenization by the alkali metal promoted the growth rate of the\nTMDs along the in-plane direction, enabling the full coverage of the\nmonolayer MoSe₂ film with negligible few-layer regions.\nNote that the fully selenized monolayer MoSe₂ with high\ncrystallinity exhibited superior electrical transport characteristics\ncompared with those reported in previous works using liquid-phase\nprecursors. We further synthesized various other monolayer TMD films,\nincluding molybdenum disulfide, tungsten disulfide, and tungsten diselenide,\nto demonstrate the broad applicability of the proposed approach.