Minimizing Defects in Wafer-Scale WSe₂ Monolayers

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted great attention as they prospect of continuing Moore's law. Recent advancements in wafer-scale single crystal 2D TMD growth and device technologies have demonstrated their scalable potential and excellent electronic performance, approaching the projection made by the International Roadmap for Devices and Systems (IRDS). However, while notable progress has been achieved with n-type characteristics in MoS₂, the performance of p-type WSe₂ remains suboptimal, primarily due to the lack of efficient bottom-up synthesis methods for high-quality WSe₂ monolayers.<br/>To address this gap, we have developed a hydroxide vapor phase deposition (OHVPD) approach for synthesizing high-quality p-type monolayer WSe₂. By introducing moisture into the epitaxial process, tungsten hydroxide acts as an immediate that provides a lower sulfurization energy pathway, facilitating the growth of WSe₂ with significantly reduced point defect density. Combining this with C-plane sapphire substrates having single exposed surfaces, we have achieved 2-inch single-crystal WSe₂ with low defect density.<br/>Moreover, our systematic study of the effect of the H₂ to H₂O ratio on the quality of WSe₂ provides insight into the fundamental mechanisms at play. Scanning tunneling microscopy (STM) characterization reveals that OHVPD-WSe₂ exhibits a total defect density of 7.8×10¹¹cm^-2, an order of magnitude lower than that of conventionally grown CVD-WSe₂. Optical characterizations, including cryogenic photoluminescence (PL), show negligible defect emission, confirming its intrinsic properties. Field-effect transistor (FET) devices based on our OHVPD-WSe2 display typical p-type characteristics, with a peak mobility of 110 cm²V^-1s^-1 and an average mobility of 87 cm²V^-1s^-1.