Fig. 2
Impact of the gate voltage on the photodetector performance in the visible and near-infrared regimes. a Responsivity of the fabricated photodetector at a wavelength of 800 nm under a bias voltage of 20 mV. Inset figures show band diagrams for the graphene photodetector at gate voltages of −20, 22, and 65 V. The Fermi energy level (EF) and graphene Dirac point energy level (EF′) are illustrated by the dashed and solid black lines, respectively. The carrier concentration in the graphene nano-stripes used in this study is measured to be 1.8 × 1013 cm−2 when the gate is unbiased, indicating highly p-doped graphene nano-stripes at a gate voltage of −20 V. b Responsivity of the fabricated photodetector at optical wavelengths ranging from 800 nm to 1.8 μm and at gate voltages of −20, 22, and 65 V. The responsivity values at each gate voltage are divided by the photodetector responsivity at 800 nm to eliminate the influence of variations in the band diagram at different gate voltages. The dashed lines show the predicted responsivity spectra assuming interband transitions are allowed over the entire wavelength range
