Low-temperature, plasma assisted, cyclic synthesis of MoS2

Abstract

Thin film reaction based synthesis techniques are promising for large area, uniform two-dimensional transition metal dichalcogenide (TMD) layers such as MoS2. In this work, the impact of the initial molybdenum film composition (metallic versus oxidized) is explored. Alternating steps of Mo sputtering and H2S soaks are used in conjunction with plasma assisted synthesis techniques to synthesize films at low temperatures. Raman, photoluminescence, x-ray photoelectron spectroscopy, and atomic force microscopy are used to physically characterize the films' atomic structure, stoichiometry, and topography, while devices were fabricated to characterize their electronic properties. MoS2 synthesized from metallic Mo films were found to exhibit better atomic and electronic structure than MoS2 synthesized from MoOx films. Additionally, slowing the rate of synthesis by segmenting growth into repeating cycles resulted in much higher film quality. To understand the impact of atomic structure and stoichiometry on device performance, films synthesized at low temperature were exposed to various high temperature annealing conditions to induce changes in film structure and composition. Physical and electrical characterization reveal that stoichiometry has a significantly weaker influence on electronic performance than grain size and atomic structure. These results provide valuable information on the optimization of low temperature thin film reactions for TMD syntheses.