Photo-Induced Electrical Gating with the Inserting of an Interfacial Carrier Blocking Layer for Organic/Graphene Phototransistors

Although ultrahigh photoconductive gain is achieved in organic semiconductor-sensitized graphene phototransistors, the response speed is limited by the photo-induced carrier injection at the organic/graphene interface. In this work, an insulating hexagonal boron nitride layer is inserted between the organic heterostructure and graphene to block the interfacial carrier transport. Above the h-BN layer, the organic heterostructure is adopted as the light-absorbing layer, and the photoresponse of graphene is realized through electrical gating of the atop h-BN dielectric layer, by the accumulated carriers in the organic heterostructure. Under this "photo-induced electrical gating" mechanism, the recombination of nonequilibrium carriers takes place only within the organic heterostructure. Furthermore, monolayer perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) is deposited on graphene before transfer of the h-BN, by which the interfacial encapsulated bubbles are effectively reduced. As a step further, the trap states are pre-filled with background light illumination, then the carrier recombination follows the band-to-band pathway. Finally, the response time of the organic/h-BN/graphene phototransistor is reduced to 7.15 ms, and a high photoresponsivity is achieved even though the carrier multiplication is sacrificed, which is reconciled by the improvement of the device quantum efficiency. The h-BN interfacial insulating layer blocks the carriers transporting between the organic layers and the graphene channel. Photoresponse of the graphene phototransistor is realized through electrical gating of the h-BN layer, generated by the photo-induced carriers accumulated in the organic layer upon h-BN. The device response speed is accelerated effectively under the "photo-induced electrical gating" working mechanism. image