Ultra-broadband self-powered reduced graphene oxide photodetectors with annealing temperature-dependent responsivity

Self-powered ultra-broadband photothermoelectric photodetectors based on free-standing reduced graphene oxide (RGO) films annealed under various temperatures (200-1000 degrees C) are developed for the first time. The preparation process of the free-standing RGO films is simple, low-cost, and scalable. An interesting phenomenon was found that with increasing annealing temperature, responsivities of RGO-based photodetectors decreased across the ultra-broadband range from ultraviolet (375 nm) to terahertz (118.8 mu m) regions. The dependence of device responsivity on annealing temperature is derived from differences in the oxygen functional groups present on the RGO films. The negative sheet Hall coefficients of the annealed RGO films confirmed that they behaved as n-type semiconductors, indicating that electron-donating groups dominated in all the annealed free-standing RGO films. The content of electron-donating groups gradually decrease as the annealing temperature rose. The response times of our devices (<50 ms) are approximately one to three orders of magnitude faster than the reported ultra-broadband photodetectors based on supported RGO films and silicon-based heterojunctions. Since our photodetectors are macro-electronic devices, the response time could be further decreased by reducing the channel length. Considering the properties of self-powered, low cost, easy preparation, and ultra-broadband response, our RGO photodetectors have potential applications for integrated optoelectronics. (C) 2019 Elsevier Ltd. All rights reserved.