The doping mechanism and electrical performance of polyethylenimine‐doped MoS₂transistor

Abstract

We present a systematic investigation of polyethylenimine (PEI) doping mechanism and its effects on the multilayer MoS 2 field effect transistors (FETs). The threshold voltages of MoS 2 FETs before (i.e., pristine) and PEI doping are observed at 3.7 and 0.72 V, respectively. This negative threshold voltage shift clearly reveals that the PEI molecules effectively act as n‐type dopants. The electrical properties are improved by absorption of PEI molecules onto MoS 2 channel because the width of Schottky barrier (SB) is narrowed by the induced interfacial dipole between PEI molecules and MoS 2 layers. Through the density function theory (DFT) calculation and X‐ray photoelectron spectroscopy (XPS) analysis, we confirm that formation of MoN bond generates new energy state into the bandgap. Consequently, the hole carriers can easily tunnel through the barrier under negative gate voltage. Furthermore, PEI doping improve photoresponsivity and time‐resolved photo‐switching characteristics because of the new energy state. Our studies demonstrate the PEI doping method has a great potential for improving electrical and optical properties of MoS 2 ‐based devices.