Graphene Quantum Dot-Decorated Vertically Oriented Graphene/Germanium Heterojunctions for Near-Infrared Photodetectors

Two-dimensional graphene films and graphene derivatives have attracted broad interest because of the large potential in optoelectronic applications. However, improving the performance of photodetectors based on graphene films and graphene derivatives remains a great challenge. Through replacing graphene films with vertically oriented graphene (VOG), which is subsequently functionalized with graphene quantum dots (GQDs), a functional VOG is assembled on the germanium (Ge) heterojunction (designated as GQDs/VOG/Ge) for near-infrared light detection. The properties of the photodetector are enhanced by the synergistic effects of GQDs and VOG with regard to light absorption and electron transport. Functional modification of VOG is an efficient way to adjust and control the Fermi level of VOG, increase the built-in potential of the Schottky junctions, and facilitate separation of photoinduced electron and hole pairs. The as-fabricated photodetector shows excellent responsivity (1.06 × 106 AW-1) and detectivity (2.11 × 1014 cm Hz1/2 W-1) at a wavelength of 1550 nm. Investigation of the photoresponse reveals response rates with microsecond rise/fall time in addition to excellent reproducibility and long-term stability. The results reveal a simple strategy to fabricate novel structures for high-performance graphene-based photodetectors.