## 1 Introduction  
The extraordinary characteristics of two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted significant attention for use in optoelectronics and electronic applications. The performance of these field-effect transistors (FETs) based on van der Waals materials has been widely studied and, accordingly, various attempts have been made to seek rare and novel properties in 2D TMDs, including adjustments of electrical parameters, such as threshold voltages, mobilities, and bandgaps [1, 2, 3, 4, 5]. Among numerous 2D TMDs, 2H-MoTe\({}_{2}\) has been known to possess a bandgap ranging from the visible to near-infrared regions, theoretically 0.83 eV (indirect) [6] and 1.13 eV (direct); the bandgap value is similar to that of silicon with 1.1 eV [4]. In addition to a bandgap close to that of Si, it possesses high carrier mobility and a low phase transition barrier, and thus it can be made metallic or semiconductive through various methods, such as laser irradiation, plasma treatment, temperature control, and tellurisation reaction [7, 8, 9, 10, 11]. The intrinsic n-type behaviour of multi-layered MoTe\({}_{2}\) devices is attributed to tellurium vacancies [6]. MoTe\({}_{2}\) originally shows n-type behaviour but undergoes charge transfer when exposed to air due to the adsorption of water and oxygen molecules, the oxygen/water redox couple being known to suppress electron conduction in FETs [6, 12]. Similar to other 2D TMDs, MoTe\({}_{2}\) shows thickness-dependent behaviour, which changes from hole-dominantto electron-dominant with increasing channel thickness [13]; this conduction mechanism of MoTe\({}_{2}\) is attributed to Schottky barrier height modulation and related bandgap alignment and the resulting band bending at the interface [4]. Therefore, depending on the channel thickness, the MoTe\({}_{2}\) device intrinsically exhibits hole-dominant carrier transport in air; the device is turned on at a negative gate bias. Despite the aforementioned favourable features of MoTe\({}_{2}\) as a switching device, it usually exhibits an on state at zero gate bias, even without any post treatment, which is undesirable in functional electronic device applications [14, 15]. This behaviour of the MoTe\({}_{2}\) channel shown in numerous previous studies raises a concern about its potential as a switching device in integrated circuits because the device should preferably be in the off state at zero gate bias to reduce standby power consumption. Compared with unipolar transistors, controlling the threshold, onset, and flat-band voltages is essential in ambipolar transistors, where both n- and p-type transistors should be highly functional and reliable for use in CMOS applications. Therefore, achieving a normal off state can be critical, particularly when a single conductive channel can serve as both \(n\)- and p-type transistors. As Te vacancies are highly sensitive to oxygen absorption and disassociation, various doping methods have been proposed [13, 16, 17, 18, 19]. However, the oxidative nature of MoTe\({}_{2}\) devices and their interactions with oxygen molecules under various conditions have not yet been fully explored. Surface charge transfer by oxygen can be a non-destructive and practical doping method once reliable control over dopability is achieved. Herein, we suggest a facile doping technique that holds considerable potential for low-dimensional nanomaterials whose applications have been restricted by physisorption- or chemisorption-induced doping. Simply annealing the MoTe\({}_{2}\) FETs on a hot plate at 100 \({}^{\circ}\)C for a short duration yields a stable shift in the charge neutrality point, which makes them a promising candidate for switching applications. Shifting the charge neutrality point thus leads to the tuning of the threshold voltage of the MoTe\({}_{2}\) FETs, which is pivotal for realising robust digital circuits.