Large-Area Metal-Semiconductor Heterojunctions Realized via MXene-Induced Two-Dimensional Surface Polarization

Direct MXene deposition on large-area 2D semiconductor surfaces can provide design versatility for the fabrication of MXene-based electronic devices (MXetronics). However, it is challenging to deposit highly uniform wafer-scale hydrophilic MXene films (e.g., Ti₃C₂T_x) on hydrophobic 2D semiconductor channel materials (e.g., MoS₂). Here, we demonstrate a modified drop-casting (MDC) process for the deposition of MXene on MoS₂ without any pretreatment, which typically degrades the quality of either MXene or MoS₂. Different from the traditional drop-casting method, which usually forms rough and thick films at the micrometer scale, our MDC method can form an ultrathin Ti₃C₂T_x film (ca. 10 nm) based on a MXene-introduced MoS₂ surface polarization phenomenon. In addition, our MDC process does not require any pretreatment, unlike MXene spray-coating that usually requires a hydrophilic pretreatment of the substrate surface before deposition. This process offers a significant advantage for Ti₃C₂T_x film deposition on UV-ozone- or O₂-plasma-sensitive surfaces. Using the MDC process, we fabricated wafer-scale n-type Ti₃C₂T_x-MoS₂ van der Waals heterojunction transistors, achieving an average effective electron mobility of ∼40 cm²·V^-1·s^-1, on/off current ratios exceeding 10⁴, and subthreshold swings of under 200 mV·dec^-1. The proposed MDC process can considerably enhance the applications of MXenes, especially the design of MXene/semiconductor nanoelectronics.