Intact Vertical 3D–0D–2D Carbon-Based p–n Junctions for Use in High-Performance Photodetectors

Ultrathin 2D graphene (2D-Gr) sheets have inherently weak absorption characteristics (only 2.3%). Pristine-graphene-based photodetectors therefore have short carrier lifetimes and small Schottky barriers that severely restrict their practical application. In this work, chemical vapor deposition (CVD) and dynamic plasma-assisted CVD (PACVD) are used to grow vertical p–n junctions in situ, which can then be used to form novel near-infrared photodetectors. The directly formed vertical heterostructures feature 0D C₃N quantum dots (QDs) in the middle position which acts as nucleation seeds to directly and rapidly grow 3D graphene (3D-Gr) structures that act as the n-type region. The bottom layer consists of a single-crystal 2D-Gr film that forms the p-type region. The large built-in electric field at the interface of the depletion region of the 3D-Gr/2D-Gr vertical p–n junction leads to the rapid separation of any photogenerated electron–hole pairs. Thus, the photodetector exhibits an excellent responsivity of 2.98 × 10⁷ A W⁻¹ and a detectivity of 1.04 × 10¹³ cm Hz^1/2 W⁻¹ at a wavelength of 1550 nm. The response speed of the photodetector is ultrafast and exceeds that of other vertical/lateral p–n-junction-based photodetectors. Its speed is ascribed to the synergism that exists between the C₃N QDs and 3D-Gr due to their unique electron distributions and structural distortions. The research paves the way for a novel class of high-performance graphene-based photodetectors with hybrid architecture.