α-MoO₃ as a Conductive 2D Oxide: Tunable n-Type Electrical Transport via Oxygen Vacancy and Fluorine Doping

Layered transition metal oxides remain a relatively unexplored front in the study of two-dimensional (2D) van der Waals materials, providing opportunities to further advance semiconductor physics and devices in a novel class of atomically thin crystals. It is usually uncommon to observe tunable electronic characteristics or achieve field effect control in these materials, given their wide band gaps and insulating nature. However, when these oxides are manipulated via doping or intercalation with new ion species, the band gap, carrier concentration, and field effect mobility can be affected, as well. Herein, we conduct a study to dope multilayer nanoflakes of α-MoO₃ with H⁺ ion intercalation, which creates oxygen vacancies and facilitates n-type conduction. Devices are characterized with controllable electron densities in the range of 10¹⁹-10²¹/cm³ and field effect gating behavior with typical field effect mobilities of 0.1 cm²/Vs. Furthermore, both wet-etching and dry-etching techniques are conducted to dope the lattice with F ions. It is found that fluorine doping is an effective reversible method to produce devices with enhanced ON-OFF switching capability during electrical gating. These advancements in controlling the n-type conductivity of nanostructured α-MoO₃ may further enhance its potential in various applications such as sensing, catalysis, or as flexible electrodes in batteries.