High Mobility of Graphene-Based Flexible Transparent\nField Effect Transistors Doped with TiO₂ and Nitrogen-Doped\nTiO₂

Abstract

Graphene\nwith carbon atoms bonded in a honeycomb lattice can be\ntailored by doping various species to alter the electrical properties\nof the graphene for fabricating p-type or n-type field-effect transistors\n(FETs). In this study, large-area and single-layer graphene was grown\non electropolished Cu foil using the thermal chemical vapor deposition\nmethod; the graphene was then transferred onto a poly­(ethylene terephthalate)\n(PET) substrate to produce flexible, transparent FETs. TiO₂ and nitrogen-doped TiO₂ (N-TiO₂) nanoparticles\nwere doped on the graphene to alter its electrical properties, thereby\nenhancing the carrier mobility and enabling the transistors to sense\nUV and visible light optically. The results indicated that the electron\nmobility of the graphene was 1900 cm²/(V·s). Dopings\nof TiO₂ and N-doped TiO₂ (1.4 at. % N) lead\nto n-type doping effects demonstrating extremely high carrier mobilities\nof 53000 and 31000 cm²/(V·s), respectively. Through\nUV and visible light irradiation, TiO₂ and N-TiO₂ generated electrons and holes; the generated electrons transferred\nto graphene channels, causing the FETs to exhibit n-type electric\nbehavior. In addition, the Dirac points of the graphene recovered\nto their original state within 5 min, confirming that the graphene-based\nFETs were photosensitive to UV and visible light. In a bending state\nwith a radius of curvature greater than 2.0 cm, the carrier mobilities\nof the FETs did not substantially change, demonstrating the application\npossibility of the fabricated graphene-based FETs in photosensors.