Sulfidation characteristics of amorphous nonstoichiometric Mo-oxides for MoS2 synthesis

Highlights: • Sulfidation characteristics of amorphous MoO_3−x films evaporated from MoO₃ and MoO₂ are compared. • More largely-reduced MoO_3−x is appropriate for formation of a continuous MoS₂ film. • Thickness and sulfidation temperature are optimized to produce a MoS₂ monolayer. • Operation of bottom-gated transistors with a synthesized MoS₂ film is demonstrated. In this study, the thermal sulfidation characteristics of two amorphous nonstoichiometric Mo-oxide (MoO_3−x) films were investigated that were deposited using e-beam evaporation of MoO₃ and MoO₂ powders. It was observed that evaporation of MoO₂ produced an amorphous MoO_3−x film that exhibited a greater number of low oxidation states than that obtained by MoO₃ evaporation. Moreover, subsequent sulfidation allowed the formation of a continuous MoS₂ film; meanwhile, the MoO₃-evaporated sample transformed into a discontinuous MoS₂ film. Both the initial thickness of the MoO₂-evaporated film and the sulfidation temperature were varied to determine their effects on the final MoS₂ film quality. The sulfidation of an approximately 1-nm-thick MoO₂-evaporated film at 780 °C produced a predominantly monolayer MoS₂ film. Further, an operation of the bottom-gated transistor arrays using the synthesized MoS₂ film was demonstrated along with a preliminary experimental result for potential application in three-dimensional device integration.