Efficient doping modulation of monolayer WS₂ for optoelectronic applications

Transition metal dichalcogenides (TMDCs) belong to a subgroup of two-dimensional (2D) materials which usually possess thickness-dependent band structures and semiconducting properties. Therefore, for TMDCs to be widely used in electronic and optoelectronic applications, two critical issues need to be addressed, which are thickness-controllable fabrication and doping modulation of TMDCs. In this work, we successfully obtained monolayer WS₂ and achieved its efficient doping by chemical vapor deposition and chemical doping, respectively. The n- and p-type dopings of the monolayer WS₂ were achieved by drop coating electron donor and acceptor solutions of triphenylphosphine (PPh₃) and gold chloride (AuCl₃), respectively, on the surface, which donates and captures electrons to/from the WS₂ surface through charge transfer, respectively. Both doping effects were investigated in terms of the electrical properties of the fabricated field effect transistors. After chemical doping, the calculated mobility and density of electrons/holes are around 74.6/39.5 cm²·V^-1·s^-1 and 1.0×10¹²/4.2×10¹¹ cm^-2, respectively. Moreover, we fabricated a lateral WS₂ p-n homojunction consisting of non-doped n-type and p-doped p-type regions, which showed great potential for photodetection with a response time of 1.5 s and responsivity of 5.8 A/W at V_G=0 V and V_D=1 V under 532 nm light illumination.