Research / 2021 / Article / Fig 3

Research Article

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

Figure 3

Material characterization of Nb-doped p-type WS2. (a) The XPS fine spectra of as-deposited and annealed 400-cycle WS2 with 30-cycle Nb doping. WS2, WS2+x, and NbS2 were all observed in as-deposited Nb-doped WS2 film. After annealing, only WS2 and NbS2 were observed, indicating the effective doping. (b) The Raman spectra of 400-cycle WS2 with Nb doping varying from 10 to 100 cycles. A blue shift of A1g peak was observed when increasing doping concentration, implying the stiffening of Nb-doped WS2 lattice with Nb-S bonds. (c) The hall mobility and resistivity of WS2 and Nb-doped WS2 with 50-cycle Nb doping at temperature varying from 50 K to 300 K. (d) The mobility, resistivity, and TOF-SIMS of WS2 and Nb-doped WS2 with Nb doping of 15, 20, and 100 cycles. After 15-cycle Nb doping, the carrier type changed from electrons to holes, and the mobility decreased one order of magnitude, while the resistivity increased 4 orders of magnitude. However, with increasing Nb doping, the mobility continued to decrease, while the resistivity started to decrease. The normalized Nb secondary ion intensity of Nb-doped WS2 films indicated the occurrence of p-type doping.