Barrier-Assisted Plasma Doping for Spatially Selective Resistance Engineering in MoS₂ Transistors

Atomically thin transition-metal dichalcogenides (TMDs) are promising channel materials for low-power logic. However, the absence of scalable and region-selective doping techniques leads to excessive local resistances that hinder the technological readiness of 2D transistors. Here, a barrier-assisted NH₃ plasma process is demonstrated that enables degenerate n-type doping of monolayer MoS₂ while preserving its crystallinity. The ultrathin pV3D3/Al₂O₃ dielectric stack not only blocks plasma-induced damage but also functions as a chemical filter that permits NH_x radicals to diffuse through. Through this doping process, an electron density of 4.3 × 10¹³ cm^-2 is achieved, yielding a contact resistance of 1.45 kΩ·µm. Density functional calculations show that NH₂ radicals adsorbed on the pristine MoS₂ surface are the main source of n-type doping while NH radicals can heal S-vacancy defects. Leveraging the spatial selectivity of this approach, mobility and on-current are enhanced by 5.8-fold with negligible threshold-voltage shift. Extension-region activation further suppresses series resistance, increasing the on-current by 260-fold (V_DS = 0.05 V) while maintaining enhancement-mode operation. These findings establish barrier-assisted NH₃ plasma doping as a promising approach for enabling high-performance n-type 2D transistors and advancing future energy-efficient 2D CMOS technology.