Synergistic hole-doping on ultrathin MoTe₂ for highly stable unipolar field-effect transistor

Despite an appropriate energy bandgap and potential to achieve unipolar p-type from initial ambipolar, the oxidative sensitivity nature of monolayer MoTe₂ has hindered its further device development for practical electronic and optoelectronic applications. Here, we demonstrate a facile superacid (TFSI) doping approach to construct a highly stable unipolar p-type MoTe₂ at the atomically thin limit, without harnessing its structure. From Raman analysis, a controllable hole-doping effect of MoTe₂ is evident by tuning the TFSI molarity (м). Considerable shifts and sharpening in A_1g peaks were observed, indicating the p-doping effect induced by TFSI treatment. When combining this technique with PMMA encapsulation, the obtained monolayer MoTe₂ field-effect transistor (FET) displays dramatic conversion from ambipolar to unipolar p-type, high on/off ratio of 10⁶, and mobility increases of up to 250 times, which is among the highest mobility increment factor to date. By integrating X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and atomic force microscopy techniques, it is further clarified that the hydrogen bonds between PMMA and TFSI are a key mechanism to enable oxidation prevention while also synergizing the doping effect of TFSI via an efficient electron-withdrawing network on monolayer MoTe₂ FET.