Characterization and Modeling of Interfacial Photogating Effect in Graphene Field-Effect Transistor Photodetectors on Silicon.

Infrared photodetection of silicon is prevented by the bandgap energy at wavelengths longer than approximately 1100 nm (∼1.12 eV) at room temperature, while silicon is the most used in modern electronics. Of particular interest is the performance of silicon for photodetectors in the infrared region beyond the silicon bandgap. Here, we demonstrate graphene field-effect transistor photodetectors on silicon with high photoconductive gain and photodetection capability extending to the infrared region. These devices have a photoresponsivity of >10 A/W for excitation above the silicon bandgap energy and yield a value of 35 A/W for infrared detection at a wavelength of 1530 nm. The high photosensitivity of the devices originates from the photogating effect in the nanostructures and a long Urbach tail extending into the infrared region. A model to explain the mechanism of the photoconductive gain is proposed, which shows that the gain results from modulation of the surface charge region under illumination. The gain strongly depends on the excitation power, due to carrier capture processes occurring over the barriers associated with the surface charge region, in agreement with the experimental data. This model properly explains the photoresponse behavior of graphene field-effect transistors on silicon.