Doped WS2 transistors with large on-off ratio and high on-current

Doping of two-dimensional (2D) transition metal dichalcogenides (TMDs) is needed to adjust the threshold voltage (V T ) and to increase the current drive by reducing both the channel and sheet resistances [1] . However, doping in TMDs often results in a sharp degradation in the on-off ratio of the field-effect transistors (FETs) [2] , [3] . Tungsten disulfide (WS 2 ) is a layered TMD with a large band-gap (> 2 eV in bilayers [4] ). We show a stable n-type doping technique using sub-stoichiometric Aluminum oxide (AlO X ) [5] in exfoliated bilayer WS 2 transistors which results in the highest reported per-layer on-current for WS 2 (80 µA/µm per layer) while retaining the high on-off ratio (10 8 ) and low off-current (≈ 5x10 -13 A/μm). Modelling these devices reveals a large interfacial trap density (1×10 13 cm 2 eV -1 ) and a high Schottky barrier height (SBH) at the contacts (0.4 eV).