## 3 Results and Discussion
### Field-Effect Transistor Device Characterization
The electron mobility (\(\mu\)) is given by the field-effect mobility, which is defined from the linear region of a \(I_{\text{drain}}-V_{\text{G}}\) curve with a slope of \(g_{m}\) as \(\mu=g_{m}(L/W)(1/C_{\text{ox}}V_{\text{DS}})\) where \(C_{\text{ox}}\) is the oxide capacitance per unit area [53]. Figure 6f shows that \(\mu\) decreased from \(\sim\)0.15 cm\({}^{2}\)/V\(\cdot\)s (Dev1) to \(\sim\)0.03 cm\({}^{2}\)/V\(\cdot\)s (Dev4) as the irradiation effects were applied more significantly probably since the defect created by the FLI process may play a role as a scattering center or a carrier trap [55]. The relatively low RT \(\mu\) is probably due to the interfacial charge traps between the MoS\({}_{2}\) channel and substrate and is expected to increase with decreasing temperature by suppressing phonon scattering [53]. The \(\mu\) could be enhanced by improving the metal/ML-MoS  
Figure 6: Variations in field-effect transistor (FET) characteristics of ML-MoS\({}_{2}\)-based FET devices by the area-selective FLI process: (**a**) An OM plan-view image of the four FET devices (Dev1–4) based on a single ML-MoS\({}_{2}\) flake. The red dashed circle indicates that the irradiation center was located inside the Dev4 channel. (**b**) The drain current vs. gate voltage (\(I_{\text{drain}}\) vs. \(V_{\text{G}}\)) curves measured from the devices at the drain-to-source voltage (\(V_{\text{DS}}\)) of 50 mV. (**c**) The set of \(I_{\text{drain}}\) vs. \(V_{\text{DS}}\) plots of the four devices at \(V_{\text{G}}=0\). From the \(I_{\text{drain}}\) vs. \(V_{\text{G}}\) data in (**b**), the following important device parameters and electronic properties of the ML-MoS\({}_{2}\) channels can be extracted: (**d**) channel conductivity (\(\sigma\)) at \(V_{\text{G}}=100\) V, (**e**) subthreshold voltage (\(V_{\text{th}}\)), (**f**) electron mobility (\(\mu\)), and (**g**) electron carrier concentration (\(n_{\text{2D}}\)). The distance \(d\) in (**d**–**g**) indicates the locations of the Dev1–4 along the dashed line parallel to the channel length from the origin 0 in the center line of the Dev1 channel as described in (**a**). Note that in (**g**), the \(n_{\text{2D}}\) values should be multiplied by \(10^{12}\). contacts, optimizing interface and surface states, and adopting the device design suitable for high-mobility devices [53; 55; 56; 57]. Moreover, by gentle annealing, \(\mu\) could be improved up to \(\sim\)0.40-0.50 cm\({}^{2}\)/V-s in the case of pristine channels (Figure S4). More importantly, Figure 6g shows that the electron carrier concentration (\(n_{\text{2D}}\)) for the 2D system calculated from \(n_{\text{2D}}=\sigma/e\mu\) decreased from 7.74 \(\times\) 10\({}^{12}\) cm\({}^{-2}\) (Dev1) to 2.87 \(\times\) 10\({}^{12}\) cm\({}^{-2}\) (Dev4) by \(\sim\)62.9% with the irradiation intensity increases (with increasing _d_) [53]. The \(n_{\text{2D}}\) value in the pristine state (Dev1), quite consistent with the literature value of \(\sim\)10\({}^{13}\) cm\({}^{-2}\), may justify these analyses based on the FET characterization [58]. Accordingly, it is verified that the p-type doping effects based on the interaction between point defects and gas molecules could be amplified by the FLI process [25; 26; 32]. Moreover, it should be noted that \(\sigma\) was degraded rapidly by the FLI process since both \(\mu\) and \(n_{\text{2D}}\) decreased simultaneously. These results show that the FLI process enables tuning electrical device properties of ML-MoS\({}_{2}\)-channel-based FETs exploiting defect-assisted p-type doping effects, consistently with the results of ambient PL experiments. Via the advanced post-fabrication annealing process, it would be possible to improve the device performance of FLI-treated FET channels further in terms of hysteresis and \(\mu\).