We present a method for substitutional p-type doping in monolayer (1L) and few-layer (FL) WS2 using highly reactive nitrogen atoms. We demonstrate that the nitrogen-induced lattice distortion in atomically thin WS2 is negligible due to its low kinetic energy. The electrical characteristics of 1L/FL WS2 field-effect transistors (FETs) clearly show an n-channel to p-channel conversion with nitrogen incorporation. We investigate the defect formation energy and the origin of p-type conduction using first-principles calculations. We reveal that a defect state appears near the Fermi level, leading to a shallow acceptor level at 0.24 eV above the valence band maximum in nitrogen-doped 1L/FL WS2. This doping strategy enables a substitutional p-type doping in intrinsically n-type 1L/FL transition metal dichalcogenides (TMDCs) with tunable control of dopants, offering a method for realizing complementary metal-oxide-semiconductor FETs and optoelectronic devices on 1L/FL TMDCs by overcoming one of the major limits of TMDCs, that is, their n-type unipolar conduction.
Keywords: atomic nitrogen; field-effect transistor; first-principles calculations; p-type WS2; substitutional doping; two-dimensional transition metal dichalcogenides.