Modification of graphene photodetector by TiO₂ prepared by oxygen plasma

Single-layer graphene has been proved to be an ideal material for broadband high-speed photodetector. However, the pure graphene photodetector photoresponsivity is limited to tens of mA/W by the low optical absorption and short exciton life of graphene. When higher responsivity is needed, the graphene layer needs to be coupled with other materials, e.g., Titanium Dioxide (TiO₂). Conventional TiO₂ recipes require either solution or high temperature which tends to destruct the graphene layer. In this work, TiO₂ is synthesized by oxygen plasma treating Ti film. This novel synthesis route of TiO₂ avoids defects introduced by the conventional recipes. The hybrid device shows a high photoresponsivity of ~ 179 A/W, a fast response time of ~ 20 ms and a specific detectivity of ~ 9.12 × 10⁹ Jones with the incident light intensity of sub-microwatt. Under the illumination, the photon absorption in graphene creates electron–hole pairs, which were separated at TiO₂/graphene interface by an internal electric field and corresponding electrons transfer from the graphene to TiO₂ layer. The high photoresponsivity is attributed to the long lifetime of the photoexcited charge carriers caused by a built-in field at the interface of TiO₂/graphene. Our research provides an effective method to improve the photoresponse of the graphene-based photodetector. In addition, our TiO₂ recipe could be applied in the fabrication of other electronic devices where solution or high temperature processes are difficult.