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-basedfield-effect transistors (FETs), high-performance p-type FETs areessential. In this study, we applied surface charge-transfer dopingfrom WO x , which has a large work functionof similar to 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 contactand injecting holes into the valence band, the p-type conversion ofintrinsically n-type trilayer WSe2 FET was successfullyachieved. However, trilayer WS2 did not show clear p-typeconversion because its valence band maximum is 0.66 eV lower thanthat of trilayer WSe2. Although inorganic WO x boasts high air stability and fabrication processcompatibility due to its high thermal budget, the trap sites in WO x cause large hysteresis during back gateoperation 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 hysteresiswas achieved.