p-Type Conversion of WS 2 and WSe 2 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 WO x , which has a large work function of ∼6.5 eV, selectively to the access region of WS 2 and WSe 2 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 WSe 2 FET was successfully achieved. However, trilayer WS 2 did not show clear p-type conversion because its valence band maximum is 0.66 eV lower than that of trilayer WSe 2 . Although inorganic WO x boasts high air stability and fabrication process compatibility due to its high thermal budget, the trap sites in WO x cause large hysteresis during back gate operation of WSe 2 FETs. However, by using top gate (TG) operation with an h -BN protection layer as a TG insulator, a high-performance p-type WSe 2 FET with negligible hysteresis was achieved.