The continued scaling of silicon transistors faces major challenges due to leakage current increase and on/off ratio degradation from short-channel and medium tunneling effect. Two-dimensional semiconductors offer potential for high-speed, low-power switching at small nodes. However, achieving wafer-scale modulated-doped monolayer transition metal dichalcogenides films remains difficult, as conventional doping techniques like high-temperature diffusion and ion implantation are incompatible with atomic-thin 2D materials.
The research team has developed a novel metal-assisted van der Waals epitaxy technique, successfully fabricating wafer-scale monolayer MoS2 films and achieving precise substitutional doping. Utilizing a self-designed chemical vapor deposition (CVD) system and industry-compatible c-plane sapphire substrates, the team achieved uniform doping with transition metals such as iron, niobium, copper, and vanadium. Chloride-based precursors ensured high doping efficiency, energy-dispersive spectroscopy confirmed macroscopic homogeneity, and high-resolution microscopy verified atomic-scale uniformity.
This doping strategy successfully modulated the electronic properties of MoS2: transition metal dopants introduced controllable impurity states within the MoS2 bandgap, enabling n-type (Fe doping) and p-type (Nb/Cu/V doping) conductivity via Fermi level shifting – a mechanism corroborated by density functional theory calculations, X-ray photoelectron spectroscopy, and photoluminescence studies. Crucially, for Fe-doped MoS2, second-harmonic generation imaging and atomic-resolution microscopy revealed that these films consist of seamlessly stitched, unidirectionally aligned domains without in-plane grain boundaries, achieving a true single-crystal structure across the entire wafer.
The doped MoS2 films exhibited exceptional electrical properties: Fe-doped transistors demonstrated an electron mobility of up to 71.2 cm2V-1s-1 and an on/off current ratio exceeding 108, outperforming pristine MoS2 and rivaling mechanically exfoliated samples. The team successfully fabricated an ultra-low-power inverter by integrating n-type (Fe-MoS2) and p-type (V-MoS2) transistors. Furthermore, by employing a gate-last process, they integrated approximately 265 thousand top-gate transistors on a 4-inch sapphire wafer, demonstrating uniform device performance and exploring digital logic applications through simulations. This breakthrough paves a viable path for the industrial-scale production of electronic devices based on two-dimensional semiconductors.
