A fresh-bias photoresponse of graphene field-effect transistor: An electrical tunable fast dipole moment generation

Abstract A unique extra photoresponse of graphene field-effect transistor to the first laser pulse after a switch of back-gate voltage (VBG) is reported and explored here. It is referred as fresh-bias photoresponse (FBPR). FBPR suggests a unique prompt charge transfer process triggered by laser illumination with the help of the VBG and the transferred charge holds as far as the VBG holds unchanged. The responsible charge transfer process is proposed between ester oxygen and carbonyl carbon atoms in the ester side chains of poly(methyl methacrylate) (PMMA) molecule. The proposed mechanism explains perfectly all of the features of FBPR. The charge transfer process generates the inter-molecular dipole moment of PMMA. Such dipole moment generation is much fast than that introduced by a photo-triggered isomerization reaction of photochromic molecule, which have been used in graphene based photodetectors. This mechanism is further confirmed by the test result of a control device with mechanically exfoliated graphene channel and a control device fabricated on hexagonal boron nitride substrate. The mechanism behind FBPR may provide a new way of developing phototransistors, photodetectors or photoelectronic memory devices in the future.