A Monolayer MoS2 FET with an EOT of 1.1 nm Achieved by the Direct Formation of a High-κ Er2O3 Insulator Through Thermal Evaporation

Achieving the direct growth of an ultrathin gate insulator with high uniformity and high quality on monolayer transition metal dichalcogenides (TMDCs) remains a challenge due to the chemically inert surface of TMDCs. Although the main solution for this challenge is utilizing buffer layers before oxide is deposited on the atomic layer, this method drastically degrades the total capacitance of the gate stack. In this work, we constructed a novel direct high-κ Er₂O₃ deposition system based on thermal evaporation in a differential-pressure-type chamber. A uniform Er₂O₃ layer with an equivalent oxide thickness of 1.1 nm was achieved as the gate insulator for top-gated MoS₂ field-effect transistors (FETs). The top gate Er₂O₃ insulator without the buffer layer on MoS₂ exhibited a high dielectric constant that reached 18.0, which is comparable to that of bulk Er₂O₃ and is the highest among thin insulators (< 10 nm) on TMDCs to date. Furthermore, the Er₂O₃/MoS₂ interface (D_it ≈ 6 × 10¹¹ cm⁻² eV⁻¹) is confirmed to be clean and is comparable with that of the h-BN/MoS₂ heterostructure. These results prove that high-quality dielectric properties with retained interface quality can be achieved by this novel deposition technique, facilitating the future development of 2D electronics.