(color online) Graphene MSM photodetector. (a) Three-dimensional schematic of a graphene MSM photodetector. (b) Relative photoresponse versus light intensity modulation frequency. The 3-dB bandwidth of this photodetector is above 15 GHz. Inset: receiver eye-diagram obtained using this photodetector, showing a clear open eye (from Ref. ^[29]). (c) (Left) Energy band diagram of a graphene p–n junction used in typical photocurrent measurements. With zero bias, dc current and the bolometric current are zero. Thermoelectric and photovoltaic currents point in the same direction. (Middle) and (Right) Energy band diagrams for graphene MSM photodetector. A uniform graphene channel is subjected to a finite source–drain bias, under small and high doping levels, respectively. Thermoelectric (TE) and photovoltaic (PV) currents are opposite. At low electrostatic doping, the photovoltaic effect dominates, while at high doping levels, the bolometric effects are pronounced (from Ref. ^[28]).