  For the first time, polyethyleneimine (PEI) doping on multilayer MoS2
field-effect transistors are investigated. A 2.6 times reduction in sheet
resistance, and 1.2 times reduction in contact resistance have been achieved.
The enhanced electrical characteristics are also reflected in a 70% improvement
in ON current, and 50% improvement in extrinsic field-effect mobility. The
threshold voltage also confirms a negative shift upon the molecular doping. All
studies demonstrate the feasibility of PEI molecular doping in MoS2
transistors, and its potential applications in layer-structured semiconducting
2D crystals.
