Non-degenerate n-type doping by hydrazine treatment in metal work function engineered WSe₂ field-effect transistor

We report a facile and highly effective n-doping method using hydrazine solution to realize enhanced electron conduction in a WSe₂ field-effect transistor (FET) with three different metal contacts of varying work functions—namely, Ti, Co, and Pt. Before hydrazine treatment, the Ti- and Co-contacted WSe₂ FETs show weak ambipolar behaviour with electron dominant transport, whereas in the Pt-contacted WSe₂ FETs, the p-type unipolar behaviour was observed with the transport dominated by holes. In the hydrazine treatment, a p-type WSe₂ FET (Pt contacted) was converted to n-type with enhanced electron conduction, whereas highly n-doped properties were achieved for both Ti- and Co-contacted WSe₂ FETs with on-current increasing by three orders of magnitude for Ti. All n-doped WSe₂ FETs exhibited enhanced hysteresis in their transfer characteristics, which opens up the possibility of developing memories using transition metal dichalcogenides. (paper)