Transport Property Evolution in 2H-MoTe_2−x Mediated by Te-Deficiency-Induced Mirror Twin Boundary Networks

The 2H-MoTe₂ is a well-known layered 2D semiconductor that is considered as a promising material for next-generation microelectronic and optoelectronic devices. Te-deficiency-induced defective structures, like Te vacancy and mirror twin boundary (MTB), would be generated at elevated temperatures. However, the temperature-dependent evolution of such defects and their influence on the macroscopic electrical transport property of 2H-MoTe₂ is unclear. Herein, the semiconductor–metal transition phenomenon in 2H-MoTe_2−x mediated by the evolving disordered MTB network with increasing Te deficiency is reported on. The samples are grown by molecular beam epitaxy, while the Te deficiency is tuned by post-growth flash annealing in ultra-high vacuum. Low-temperature scanning tunneling microscope investigation discloses the medium-range disorder evolution of the MTB network incorporated in the 2H-MoTe₂, which eventually transforms to an ordered metallic Mo₅Te₈ metastable phase. The scanning tunneling spectroscopy shows rich in-gap states localized at the MTBs, which provide a conducting channel in the semiconductor. The ultra-high vacuum in situ transport measurement shows a gradual decrease of resistance of the sample upon flash annealing from 50 to 480 °C, confirming the influence of Te deficiency on the transport property, which would play an essential role in the device performance and durability.