Origin of p-type conductivity in a WSe₂ monolayer

Transition-metal dichalcogenides have promising potentials for high-performance electronic and optoelectronic applications, which could be deeply influenced by defects, including native defects and dopants. Experiments to date have frequently reported p-type conductivity in the WSe₂ monolayer, but the origin remains elusive. Here, using the first-principles calculations, we systematically investigate the point defects in the WSe₂ monolayer and show that: (1) no intrinsic point defect is responsible for the p-type doping; (2) hydrogen interstitials (H_i) are possible sources for n-type conductivity; (3) oxygen substitution of Se (O_Se) can greatly promote the formation of adjacent W vacancy (V_W), and finally make V_W relatively shallow acceptors by forming the defect complex nO_Se + V_W (n = 1 to 6). Our work reveals that nO_Se + V_W is the origin of the p-type conductivity in the unintentionally doped WSe₂ monolayer, given that O is present throughout the synthesis conditions of WSe₂.