Controlled Fabrication of Metallic MoO₂ Nanosheets towards High-Performance p-Type 2D Transistors

Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDCs) are extensively employed as channel materials in advanced electronic devices. The electrical contacts between electrodes and 2D semiconductors play a crucial role in the development of high-performance transistors. While numerous strategies for electrode interface engineering have been proposed to enhance the performance of n-type 2D transistors, upgrading p-type ones in a similar manner remains a challenge. In this work, significant improvements in a p-type WSe₂ transistor are demonstrated by utilizing metallic MoO₂ nanosheets as the electrode contact, which are controllably fabricated through physical vapor deposition and subsequent annealing. The MoO₂ nanosheets exhibit an exceptional electrical conductivity of 8.4 × 10⁴ S m^‒1 and a breakdown current density of 3.3 × 10⁶ A cm^‒2. The work function of MoO₂ nanosheets is determined to be ≈5.1 eV, making them suitable for contacting p-type 2D semiconductors. Employing MoO₂ nanosheets as the electrode contact in WSe₂ transistors results in a notable increase in the field-effect mobility to 92.0 cm² V^‒1 s^‒1, which is one order of magnitude higher than the counterpart devices with conventional electrodes. This study not only introduces an intriguing 2D metal oxide to improve the electrical contact in p-type 2D transistors, but also offers an effective approach to fabricating all-2D devices.