Tunable Doping Strategy for Few-Layer MoS₂ Field-Effect Transistors via NH₃ Plasma Treatment

Molybdenum disulfide (MoS₂) is a promising candidate for next-generation transistor channel materials, boasting outstanding electrical properties and ultrathin structure. Conventional ion implantation processes are unsuitable for atomically thin two-dimensional (2D) materials, necessitating nondestructive doping methods. We proposed a novel approach: tunable n-type doping through sulfur vacancies (V_S) and p-type doping by nitrogen substitution in MoS₂, controlled by the duration of NH₃ plasma treatment. Our results reveal that NH₃ plasma exposure of 20 s increases the 2D sheet carrier density (n_2D) in MoS₂ field-effect transistors (FETs) by +4.92 × 10¹¹ cm^-2 at a gate bias of 0 V, attributable to sulfur vacancy generation. Conversely, treatment of 40 s reduces n_2D by -3.71 × 10¹¹ cm^-2 due to increased nitrogen doping. X-ray photoelectron spectroscopy, Raman spectroscopy, and photoluminescence analyses corroborate these electrical characterization results, indicating successful n- and p-type doping. Temperature-dependent measurements show that the Schottky barrier height at the metal-semiconductor contact decreases by -31 meV under n-type conditions and increases by +37 meV for p-type doping. This study highlights NH₃ plasma treatment as a viable doping method for 2D materials in electronic and optoelectronic device engineering.