High sensitivity ultraviolet detection based on three-dimensional graphene field effect transistors decorated with TiO2 NPs

A three-dimensional (3D) ultraviolet (UV) photodetector was fabricated by decorating a tubular graphene field-effect transistor (GFET) with titanium dioxide (TiO2) nanoparticles (NPs). The unique tubular architecture not only provides a natural 3D optical resonant microcavity to enhance the optical field inside it, but also increases the light-matter interaction area. Strong UV absorption in the TiO2 NPs creates a number of electron-hole pairs, where the electrons are transferred to graphene, while the holes are trapped within the TiO2 NPs, leading to a strong photogating effect on the graphene channel conductance. The photoresponsivity of our 3D GFET photodetector decorated with TiO2 NPs was demonstrated up to 475.5 A W-1 at 325 nm, which is about 2 orders of magnitude higher than that of a 3D GFET photodetector without the TiO2 NP decoration (1 A W-1), and over 3 orders of magnitude higher than that of a recently reported UV photodetector based on the graphene/vertical Ga2O3 nanowire array heterojunction (0.185 A W-1). Moreover, the photoresponsivity and photoresponse speed of the device can be easily tuned by applying a small gate bias (<= 3 V) and/or changing the source-drain bias. These results indicate that the photoresponsivities of graphene-based photodetectors can be significantly improved by exploiting 3D graphene structures and integrating graphene with semiconducting light harvesters simultaneously.