Unintentional Doping Effects on Atomically-Thin Nb-doped MoS₂ Observed by Scanning Nonlinear Dielectric Microscopy

Two-dimensional semiconductors such as atomically-thin MoS2 have recently gained much attention because of their superior material properties fascinating for the future electronic device applications. Here we investigate the nanoscale dominant carrier distribution on atomically-thin natural and Nbdoped MoS2 mechanically exfoliated on SiO2/Si substrates by using scanning nonlinear dielectric microscopy. We show that a few-layer natural MoS2 sample is an n-type semiconductor, as expected, but Nb-doped MoS2, normally considered as a p-type semiconductor, can unexpectedly become an n-type semiconductor due to strong unintentional electron doping.