Tuning the Electronic and Optoelectronic Properties of Fermi‐Level Pinning‐Free MoS ₂ and WSe ₂ Transistors by Surface Charge Transfer Doping

Abstract Surface charge transfer doping (SCTD) can tune the carrier concentration and type in 2D materials, and thereby modulates the electronic and optoelectronic properties. This work systematically investigated the influence of SCTD on the electronic and optoelectronic properties of Fermi‐Level Pinning‐Free MoS 2 and WSe 2 transistors. The increased hole current and the decreased electron current indicated p‐type doping in WSe 2 and MoS 2 FETs induced by F 4 TCNQ doping. P‐type doping transforms the electrical contact behavior between WSe 2 or MoS 2 and gold electrodes in opposite directions: the WSe 2 ‐Au interface changes from Schottky to ohmic, while the MoS 2 ‐Au contact transitions from ohmic to Schottky. Simultaneously, p‐type doping converts recombination centers in WSe 2 into deep trap states, whereas in MoS 2 , the trap states between quasi‐Fermi levels turn into recombination centers. These combined modifications in contact resistance and defect properties lead to a notable slowing of the WSe 2 photoresponse, with rise and fall times increasing from 1.3 s/1.8 s to 15 s/18 s, while the responsivity improves from 0.5 mA/W to 2 A/W. In contrast, MoS 2 exhibits accelerated response dynamics, with rise and decay times shortening dramatically from 36 s/100 s to 0.12 s/0.01 s, accompanied by a drop in responsivity from 254 mA/W to 3 mA/W.