Wafer-Scale Single-Crystal WSe₂ Monolayers Using Substrate-Passivation-Driven Epitaxy

Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) offer a promising materials platform for next-generation electronic devices, providing ultimate subnanometer thickness control and various functionalities for advanced optoelectronics. Among 2D TMDs, p-type TMDs such as WSe₂ are essential for fabricating fully complementary metal-oxide-semiconductor (CMOS) 2D circuits. Nonetheless, achieving wafer-scale, single-orientation p-type WSe₂ monolayers is notably elusive compared with n-type MoS₂ monolayers. Herein, we report a substrate-passivation-driven epitaxy strategy that produces a 98.44% single-orientation WSe₂ monolayer on two-inch C-plane sapphire, surpassing previous benchmarks of around 82-87% ratios for single-orientation large-area p-type TMDs. By precisely tailoring the introduction sequence of H₂ gas and Se vapor for in situ substrate treatment, we engineered an AlOSe₂-Se-passivated sapphire surface that stabilizes the as-grown WSe₂ monolayer with a predominantly 30° single orientation. Optical and electrical characterization results corroborate the structural uniformity of the WSe₂ monolayers and the consistency of their device performance across wafer-scale transistor arrays. By advancing the epitaxial growth mechanism of oriented WSe₂ monolayer on sapphire, we establish this passivation-driven epitaxy strategy that can be used as a robust materials platform for scalable, single-orientation p-type TMD monolayers, bridging the performance gap between n-type and p-type 2D semiconductors for next-generation electronic and optoelectronic devices.