p-Type Conversion of WS<sub>2</sub> and WSe<sub>2</sub> by Position-Selective Oxidation Doping and Its Application in Top Gate Transistors
Ryoichi Kato, Haruki Uchiyama, Tomonori Nishimura, Keiji Ueno, Takashi Taniguchi, Kenji Watanabe, Edward Chen, Kosuke Nagashio
Abstract
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.