Graphene on Silicon-Nitride Photodetector

摘要

Even though graphene is a gapless material, it demonstrates strong interband absorption from a broad rangeof wavelengths between VIS and NIR. Recent photocurrent graphene-based detectors demonstrated strong pho-toresponse signal near the graphene/metal boundaries. To increase the response time of photodetectors, the useof low thermal capacity materials and structures are required. SiN membranes are good candidates due to theirhigh-quality factor (up to 106-107), low mass and excellent optical properties. The motivation for this studywas based on a lack of any suitable solution for nano-dimension form factor detector that could be integratedinto 3D photonic bandgap structures for real-time internal characterization.The proposed detector comprises out of 100 nm and 1 μm suspended SiN membrane in a Si chip. Twofabrication procedures were performed to deposit dissimilar metal contact. For the first instance, silver andpalladium were deposited using a lithography-free inkjet procedure in a form of macroscopic pads (Fig. 1(a)).For the second instance, an interdigitated pattern was produced by a planar masked-UV lithography approach(Fig. 1(b)). Finally, a transparent monolayer graphene sheet was applied to the surface.The detectors were characterized by exposure to VIS 515 nm and NIR 1030 nm laser radiation, the inducedcurrent was measured. When the detector is irradiated, two mechanisms which lead to charge separation andphoto-voltage or/and photo-current generation are occurring. The laser exposure causes a localised light ab-sorbance and heating, resulting in a buildup of an electric field as photo-voltage via a photo-electric (Seebeck)mechanism. Also, due to the electric field present between the two dissimilar metal electrodes, photo-generatedcarriers are subjected to external bias and photo-current is generated upon illumination. An experimentalsensitivity value up to 1 μA/W was observed.In conclusion, a new type of broad-spectrum photodetector was validated. The proposed photodetectoris inferior to the current mature silicon photodetector technology in terms of sensitivity. However, for theparticular function of detection of light inside 3D photonic structures, the low sensitivity (invisibility) is a requiredproperty. It is optically thin on the nanoscale and can be tens/hundreds of micrometers in lateral dimensions asneeded, therefore can be integrated into existing and novel photonic chips, including three-dimensional ones. Itsunprecedented form factor will be a new option for high-density 3D photonic devices.