p-Type Conversion of WS₂ and WSe₂ by Position-Selective Oxidation Doping and Its Application in Top Gate Transistors

For the complementary operation of two-dimensional (2D) material-based field-effect transistors (FETs), high-performance p-type FETs are essential. In this study, we applied surface charge-transfer doping from WOx, which has a large work function of ∼6.5 eV, selectively to the access region of WS₂ and WSe₂ by covering the channel region with h-BN. By reducing the Schottky barrier width at the contact and injecting holes into the valence band, the p-type conversion of intrinsically n-type trilayer WSe₂ FET was successfully achieved. However, trilayer WS₂ did not show clear p-type conversion because its valence band maximum is 0.66 eV lower than that of trilayer WSe₂. Although inorganic WOx boasts high air stability and fabrication process compatibility due to its high thermal budget, the trap sites in WOx cause large hysteresis during back gate operation of WSe₂ FETs. However, by using top gate (TG) operation with an h-BN protection layer as a TG insulator, a high-performance p-type WSe₂ FET with negligible hysteresis was achieved.