Photoinduced Terahertz Conductivity and Carrier Relaxation in Thermal-Reduced Multilayer Graphene Oxide Films

Graphene oxide (GO) is an attractive option for large scale production of graphene. On the other hand, the graphene obtained by the reduction of GO has inevitable structural defects, and the vacant lattice sites will significantly restrict its conductivity. It has been demonstrated that thermal annealing in hydrogen is an efficient method to reduce defects and heal the lattice in GO samples. However, it is still not clear how the defects and/or disordering influence the photoelectric conversion efficiency and the carrier relaxation pathway in GO. Herein, time-domain terahertz (THz) spectroscopy is employed to characterize the properties of the multilayer GO films which were annealed in hydrogen at various temperatures. Upon photoexcitation, a transient increase of the conductivity was observed for the reduced graphene oxide (RGO) samples. The ultrafast carrier relaxation process can be well assigned to the carrier-carrier scattering and carrier-phonon coupling. Our results demonstrated that the RGO films with fewer defects and better lattice structure are successfully manufactured. In addition, by fitting to the Drude model, several electron transport parameters, such as the carrier scattering time, carrier plasma frequency, and photoinduced conductivity, are obtained in our multilayer RGO films.