Ambipolar and Robust WSe₂ Field‐Effect Transistors Utilizing Self‐Assembled Edge Oxides

Transition metal oxides (TMOs) with high work function (WF) show promising properties as unipolar p‐type contacts for transition metal dichalcogenides. Here, ambipolar field‐effect transistors (FETs) enabled by bilayer WSe 2 with self‐assembled TMOs (WO 2.57 ) as contacts are reported. Systematic material characterizations demonstrate the formation of WO 2.57 /WSe 2 heterojunctions around nanoflake edges with Se atoms substituted by O atoms after air‐exposure, while pristine properties of WSe 2 almost sustain in inner domains. As‐fabricated FETs exhibit both polarities, implying WO 2.57 with lowered WF at edges can serve as both the p‐type and n‐type contact for inner WSe 2 . Noteworthy, greatly reduced contact resistance and enhanced channel current are achieved, compared to the devices without WO 2.57 contacts. Linear drain–source current relationship from 77 to 300 K indicates the ohmic contact between edge WO 2.57 and inner WSe 2 . Density functional theory calculations further reveal that the WO 2.57 /WSe 2 heterojunction forms a barrier‐less charge distribution. These nm‐scale FETs possess remarkable electrical conductivity up to ≈2600 S m −1 , ultra‐low leakage current down to ≈10 −12 A, robustness for high voltage operation, and air stability, which even outperform pristine WSe 2 FETs. Theoretical calculations reveal that the high conductivity is exclusively attributed to the air‐induced WO 2.57 and its further carrier injection to WSe 2 .