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., Ti 3 C 2 T x ) on hydrophobic 2D semiconductor channel materials (e.g., MoS 2 ). Here, we demonstrate a modified drop-casting (MDC) process for the deposition of MXene on MoS 2 without any pretreatment, which typically degrades the quality of either MXene or MoS 2 . 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 Ti 3 C 2 T x film (ca. 10 nm) based on a MXene-introduced MoS 2 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 Ti 3 C 2 T x film deposition on UV-ozone- or O 2 -plasma-sensitive surfaces. Using the MDC process, we fabricated wafer-scale n -type Ti 3 C 2 T x -MoS 2 van der Waals heterojunction transistors, achieving an average effective electron mobility of ∼40 cm 2 ·V -1 ·s -1 , on/off current ratios exceeding 10 4 , 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.