Research / 2021 / Article / Fig 4

Research Article

Wafer-Scale Synthesis of WS2 Films with In Situ Controllable p-Type Doping by Atomic Layer Deposition

Figure 4

The electrical properties of WS2 n-FETs and Nb-doped WS2 p-FETs. (a) CMOS-compatible process flow of FETs and schematic of device structures. (b) The transfer and output characteristics of WS2 n-FET with 2 μm gate width and the mobility distribution of 30 WS2 n-FETs. The on-current reached 0.4 μA/μm, and the on/off ratio was up to 105. (c) The transfer and output characteristics of 15-cycle Nb-doped WS2 p-FET with 2 μm gate width and the distribution of at and for 132 Nb-doped WS2 p-FETs with 25-cycle Nb doping. The carrier type changed from electron to hole, and the on-current was μA/μm. (d) The doping effects on WS2 FETs. Nb dopants varied from 1 to 20 cycles. Nb-doped WS2 FET did not show p-type behavior but with a decreased on- and off-current until reaching 15 cycles. After 20-cycle Nb doping, the device presented heavily p-type behavior, indicating the controllable doping. (e) The PBTI of WS2 n-FET at RT. The stress was set to be 5.5 V. After 1000 s stress, the on-current degraded only for 3.5%, while the was up to 300 mV. (f) The air stability of WS2 n-FET in ambient for 1, 3, and 6 months. The on-current degraded slightly within one order, while the degradation of off-current was less obvious after 3 months than that of 6 months. (g) The I-V curve of WS2/Nb-doped WS2 p-n structures with the rectifying ratio of over 104. The inset figure was rectifying ratio.