Doping-Induced Schottky-Barrier Realignment for Unipolar and High Hole Current WSe2 Devices With >108 ON/OFF Ratio

Direct evidence of O-2-plasma induced contact metal Fermi-level realignment is observed in WSe(2 )based SB field-effect transistors (FETs), leading to high hole currents with on/off ratios >10(8). The formation of tungsten oxide (WOx) converted from top WSe2 layers not only serves as an effective p-type dopant, but also unpins the Fermi-level of the metal contacts. The phenomena are corroborated by significant threshold voltage shifts, improved hole currents and suppression of the electron branch, observed from our statistical device characteristics. In addition, channel thickness dependence is investigated with the observation of complete suppression of the electron branch in thin WSe2 (<4.9nm) devices after the O-2-plasma treatment, which is interpreted as more substantial increase of SB height to the conduction band of larger bandgaps. Excellent air-stability is also concluded from statistical device results, suggesting a robust p-doping approach for WSe2 through O-2-plasma treatment.