Ultrathin GaO_x tunneling contact for 2D transition-metal dichalcogenides transistor

Interlayer insertion has emerged as one of the key strategies for contact engineering in two-dimensional (2D) field-effect transistors (FETs). However, conventional interlayers such as hexagonal boron nitride (hBN) have limitations in contact performance and face challenges in achieving low-thermal-budget large-area fabrication. In this work, we explore the functionalization of printed ultrathin gallium oxide (GaO_x) films as tunneling contact layers in 2D transistors. Leveraging self-limiting oxidation of liquid gallium, we fabricate nanometer-thick GaO_x films (3.6 nm) that possess shallow defect states arising from oxygen vacancies, thereby narrowing the tunneling barrier width. When integrated as a tunneling layer in multilayer WS₂ field-effect transistors, the GaO_x film significantly enhances device performance, achieving a record electron mobility of 296 cm²·V⁻¹·s⁻¹, an ultra-low contact resistance of 2.38 kΩ·μm, and a minimal contact barrier height of 3.7 meV. Distinct from conventional insulating tunneling dielectrics, the observed performance enhancement originates from a hybrid tunneling mechanism within GaO_x, which is activated under the synergy of multiple electric fields and temperatures. Oxygen vacancies act as dynamic conduction channels that mediate composite tunneling pathways combining defect-assisted, direct, and Fowler–Nordheim tunneling, thus enabling efficient carrier injection across the interface. In addition, the low-temperature printing method also enables van der Waals integration in scalable fabrication without the Fermi pinning effect. This study not only demonstrates the new functional application of printed GaO_x films and clarifies the role of their oxygen vacancies in the tunneling mechanism but also proposes a novel, scalable strategy for optimizing contact engineering in low-dimensional electronic devices.