Hydroxide Vapor Phase Deposition for Low-Defect-Density 2D TMDs Growth

Two-dimensional (2D) semiconducting monolayer materials such as transition metal dichalcogenides (TMDs) MX₂ (M=Mo, W; X=S, Se) are considered promising as channel materials to extend the Moore’s Law in the post-Si era. Recently, wafer-scale single-crystal TMD monolayers have been demonstrated by chemical vapor deposition (CVD), which shows homogeneous electrical performance due to the decreased grain boundaries. Nevertheless, the abundant point defects in TMD monolayers like vacancies and impurities introduced during the synthetic processes limit their electrical quality. Thus, innovative endeavors on growth reactions to realize low-defect-density growth are urgently needed. Here, we reported that adopting extremely pure metal precursor in combination with hydroxide vapor phase deposition (OHVPD) enables the growth of low-defect-density TMD monolayers. The PL spectra show the superior optical quality of OHVPD-TMD monolayers (i.e., WS₂ and MoS₂) with higher peak energies and narrower FWHM compared to conventional CVD samples. The scanning tunneling microscopy (STM) images show that the transferred OHVPD-TMD monolayers have one order of magnitude lower defect density compared to samples prepared by the CVD method. The field effect transistor (FET) devices based on OHVPD-WS₂ monolayers reach a peak electron mobility of ~200 cm²/Vs at room temperature, and ~800 cm²/Vs at 15K. The on-state current of short-channel-length devices (100 nm) reaches a value of ~400 mA/mm. Based on STM and device measurements, the as-grown high-quality TMD monolayer films are less susceptible to subsequent film transferring and device fabricating processes.