Fluorination is an effective process to open the band gap of graphene (Gr), which is beneficial to the development of optoelectronic devices working in wide wavelength. Herein, we report a dual-mode broadband photodetector (PD) by integrating fluorinated graphene (F-Gr) with silicon (Si). It is found that when working in photoconductive mode, the F-Gr/Si heterojunction exhibited a remarkable photoresponse over a wide spectral region from ultraviolet (UV), visible to near infrared (NIR) light with a high responsivity ( R) of 1.9 × 107 A W-1 and specific detectivity ( D*) of 4.4 × 1012 Jones at 650 nm. Nonetheless, both parameters will be considerably reduced when the F-Gr/Si heterojunction works in the photodiode mode. In this mode, the Ilight/ Idark ratio is as high as 2.0 × 105 and the response speed is accelerated by more than 3 orders of magnitude from about 5 ms to 6.3 μs. Notably, the responsivity of the device in the UV and NIR regions was remarkably enhanced in comparison with that of pristine Gr/Si-heterojunction-based devices. Considering the F-coverage-dependent band gap of the F-Gr revealed by the first-principle calculations, we believe that the enhancement was ascribed to the opening of the band gap in the partially fluorinated Gr, which is stabilized due to the configuration entropy as the temperature increases. The dual-mode PD enabled the simultaneous weak light detection and fast photodetection, which overcome the limitation of the traditional monomode PD.
Keywords: band gap opening; broadband; fluorinated graphene; photoconductive photodetector; photodiode.