2.4 Photodetector constructed with the monolayer graphene directly synthesized on Si substrate
Finally, we demonstrate the high-quality performance properties of three different devices directly fabricated from our monolayer graphene grown on different substrates. Figure 5a displays the schematic diagram of our as-fabricated monolayer graphene photodetectors on Si substrate. To evaluate the performance of the individual photodetector in broadband detection, both visible light (532 nm) and near-infrared light (980 nm and 1550 nm) with a fixed power density of 30 mW/cm2 are used to stimulate the graphene/Si Schottky junctions. Figure 5b shows the I-V features of our photodetectors under dark and light illumination at various wavelengths, indicating the typical current rectifications in our Schottky junctions of graphene and Si substrate.[46-47] During illumination in the Schottky junction area, a pronounced photocurrent can be seen at the reverse bias. Moreover, the generated photocurrent improves immediately as the wavelength is shortened from 1550 nm to 532 nm, demonstrating the device’s good capability for photoelectric conversion.[48]