Gate-tunable ion-electron hybrid phototransistor based on graphene/RbAg4I5 composite

A new kind of phototransistor based on graphene and superionic conductor is fabricated by depositing a layer of RbAg4I5 on transferred graphene by a vacuum thermal evaporation method. Electrons in graphene and silver ions in RbAg4I5 form ion-electron bound state (IEBS) at the interface due to Coulomb interaction. The bound state, which can be dissociated by photons, greatly influences the electronic conductivity of graphene. The binding energy between ions and electrons is an important parameter to determine the photon energy that can be absorbed to set free bound state. Through the back-gate bias, we realize controllable modulation on binding energy. The binding energy between electron and silver ion linearly decrease with the increase of gate, resulting in the increased number of IEBS that can be dissociated by photons, which are proved by both experimental measurement and theoretical analysis. Owing to the decrease in binding energy, the response amplitudes can be increased by up to two order of magnitude under the illumination of lasers. This phototransistor based on graphene and RbAg4I5 achieves controllable responsivity from several mA/W to several hundred mA/W while the response speed remains unchanged at order of 100 milliseconds. This study, on the one hand, makes us have a better understanding in the modulation of ion on electron transport; on the other hand, offers new road for us to achieve the modulation on the photo-responses, and is very promising to be applied in optoelectronic devices with current circuit technology.