Kosuke Nagashio received Ph.D. degrees in Materials Engineering from The University of Tokyo in 2002. From 2002 to 2003, he was a postdoctoral research fellow at Stanford University, California. He is currently a Professor with the Department of Materials Engineering, The University of Tokyo. His current research interests include the growth, characterization, device fabrication, and electronic transport properties of two-dimensional materials and related systems.

We elucidate the electronic origin of hidden interfacial doping in monolayer MoS₂ single-crystal wafers grown on sapphire by metal–organic chemical vapor deposition (MOCVD) and establish a transfer-free top-gate device platform. Despite structural perfection, as-fabricated devices exhibit degenerate electron doping and lack a clear off state. Hall measurements quantify an interfacial electron density of 2.7×10¹² cm⁻², evidencing substantial charge transfer across the nominal van der Waals interface. Interface-sensitive spectroscopy, lateral force microscopy, and thermal desorption analysis reveal a buried sulfate-derived layer accompanied by a water-like interfacial structure that acts as an intrinsic electron donor. A purely dry H₂/Ar annealing process selectively removes these species, suppressing charge transfer and restoring intrinsic FET characteristics without transfer or wet processing. Through this dry interface engineering approach, we demonstrate MOCVD-grown single-crystal MoS₂ wafers as a robust, transfer-free platform for the reliable evaluation of intrinsic gate stacks and device performance.

1. Y. Sakuma, and K. Nagashio, et al., “Self-aligned and self-limiting van der Waals epitaxy of monolayer MoS₂ for scalable 2D electronics,” Nature Commun., 2026, 12, 602. DOI: 10.1038/s41467-026-68320-8
2. S. Li, and K. Nagashio, et al., “MOCVD-Grown MoS₂ Wafers as a Transfer-Free Platform for Top-Gate Devices via Dry Interface Engineering,” Adv. Mater. 2026, e73931. DOI: 10.1002/adma.73931