Modification of graphene photodetector by TiO.sub.2 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 (TiO.sub.2). Conventional TiO.sub.2 recipes require either solution or high temperature which tends to destruct the graphene layer. In this work, TiO.sub.2 is synthesized by oxygen plasma treating Ti film. This novel synthesis route of TiO.sub.2 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 x 10.sup.9 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 TiO.sub.2/graphene interface by an internal electric field and corresponding electrons transfer from the graphene to TiO.sub.2 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 TiO.sub.2/graphene. Our research provides an effective method to improve the photoresponse of the graphene-based photodetector. In addition, our TiO.sub.2 recipe could be applied in the fabrication of other electronic devices where solution or high temperature processes are difficult.