The paper presents the development and characterization of ultrafast graphene photodetectors using single and few-layer graphene field-effect transistors (FETs). The authors demonstrate that graphene can absorb a significant fraction of light over a broad wavelength range, with a photoresponse that does not degrade up to high modulation frequencies of 40 GHz. This is attributed to the unique electronic and photonic properties of graphene, such as its high carrier mobility and zero bandgap. The photodetectors exhibit high internal quantum efficiency (6-16%) and zero dark current operation, making them suitable for applications in high-speed optical communications, terahertz detection, imaging, and spectroscopy. The high bandwidth of the photodetectors is primarily limited by the RC time constant rather than transit time, suggesting a potential intrinsic bandwidth of over 500 GHz. The study also discusses the mechanisms of photo-carrier generation and transport in graphene, which differ from those in conventional semiconductors, leading to superior performance in photonic devices.The paper presents the development and characterization of ultrafast graphene photodetectors using single and few-layer graphene field-effect transistors (FETs). The authors demonstrate that graphene can absorb a significant fraction of light over a broad wavelength range, with a photoresponse that does not degrade up to high modulation frequencies of 40 GHz. This is attributed to the unique electronic and photonic properties of graphene, such as its high carrier mobility and zero bandgap. The photodetectors exhibit high internal quantum efficiency (6-16%) and zero dark current operation, making them suitable for applications in high-speed optical communications, terahertz detection, imaging, and spectroscopy. The high bandwidth of the photodetectors is primarily limited by the RC time constant rather than transit time, suggesting a potential intrinsic bandwidth of over 500 GHz. The study also discusses the mechanisms of photo-carrier generation and transport in graphene, which differ from those in conventional semiconductors, leading to superior performance in photonic devices.