Tunable electrical properties of multilayer HfSe₂ field effect transistors by oxygen plasma treatment

HfSe₂ field effect transistors are systematically studied in order to selectively tune their electrical properties by optimizing layer thickness and oxygen plasma treatment. The optimized plasma-treated HfSe₂ field effect transistors showed a high on/off ratio improvement of four orders of magnitude, from 27 to 10⁵, a field effect mobility increase from 2.16 to 3.04 cm² V^-1 s^-1, a subthreshold swing improvement from 30.6 to 4.8 V dec^-1, and a positive threshold voltage shift between depletion mode and enhancement mode, from -7.02 to 11.5 V. The plasma-treated HfSe₂ photodetector also demonstrates a reasonable photoresponsivity from the visible to the near-infrared region of light.