Investigating the mechanism of hysteresis effect in graphene electrical field device fabricated on SiO₂ substrates using raman spectroscopy

The hysteresis effect is a common problem in graphene field-effect transistors (FETs). Usually, the external doping to graphene is considered to be responsible for the hysteresis behavior, but is not yet clearly understood. By monitoring the doping of graphene and the hysteresis in graphene FETs under different atmospheres using in situ Raman spectroscopy, it is confirmed that the electrochemical doping of O₂/H₂O redox couple to graphene is responsible for the hysteresis effect. In addition, Raman spectra of graphene on SiO₂ substrate show stronger doping than that suspended, which indicates that SiO₂ substrate plays an important role in the doping of graphene. Herein it is proposed that the doping species (H ₂O and O₂) are bounded at the interface of graphene/SiO₂ substrate by hydrogen-bonds with the silanol groups on SiO₂ substrate. The dynamic equilibrium process of the charge-transfer between H₂O/O₂ redox couple and graphene under electrical field modulation is carefully analyzed using Marcus-Gerischer theory. This work provides a clear view to the mechanism of the hysteresis effect, and is of benefit to a reliable design to suppress the hysteresis in graphene FETs. Electrochemical doping of the O₂/H₂O redox couple to graphene occurring at the interface of graphene/SiO₂ substrate is proven responsible for the origin of the hysteresis effect in graphene electrical field transistors. Marcus-Gerischer theory is used to explain the charge-transfer mechanism between the O₂/H₂O redox couple and graphene, and to analyze their dynamic equilibrium process under electrical field effect.