Understanding asymmetric transfer characteristics and hysteresis behaviors in graphene devices under different chemical atmospheres

Abstract

Asymmetric transfer characteristics and hysteresis behaviors are two puzzling electronic transport properties in graphene field effect transistor (GFET). Herein, we presented systematic investigations on these phenomena by varying gate voltage sweeping rates and testing chemical atmospheres. Three different doping mechanisms for GFET were proposed to illustrate these behaviors: electric field doping, molecule chemical doping, and electrochemical doping by redox reactions. In ambient environment, the plateau's emergence in asymmetric transfer curve of GFET was attributed to the counteraction between n-type electric field doping and p-type O2/H2O electrochemical doping. The hysteresis effect difference in backward sweeping varied as a function of gate voltage sweeping rate, which has been offered a qualitative explanation in the context of thermodynamics and kinetics. In NH3, the degree of hysteresis effect in GFET increased with the vapor concentration rising up, while NO2 atmosphere induced opposite behavior. Generally, the interplay of the three doping mechanisms accounts for the total Fermi level modulation and carrier migration behavior near the Dirac point. For instance, the electrochemical doping could occur spontaneously because the electric effect doping or chemical doping raised the graphene Fermi level high enough with respect to the electrochemical O2/H2O redox potential.