Control of polarity in multilayer MoTe2 field-effect transistors by channel thickness

In this study, electronic properties of field-effect transistors (FETs) fabricated from exfoliated MoTe₂ single crystals are investigated as a function of channel thickness. The conductivity type in FETs gradually changes from n-type for thick MoTe₂ layers (above ≈ 65 nm) to ambipolar behavior for intermediate MoTe₂ thickness (between ≈ 60 and 15 nm) to ptype for thin layers (below ≈ 10 nm). The n-type behavior in quasi-bulk MoTe₂ is attributed to doping with chlorine atoms from the TeCl₄ transport agent used for the chemical vapor transport (CVT) growth of MoTe₂. The change in polarity sign with decreasing channel thickness may be associated with increasing role of surface states in ultra-thin layers, which in turn influence carrier concentration and dynamics in the channel due to modulation of Schottky barrier height and band-bending at the metal/semiconductor interface.