High-performance photodetectors based on Schottky junctions formed by vertical 2D-3D-2D graphene sandwich nanocavity and germanium substrate

The inefficient light absorption and gapless features of two-dimensional graphene (2D-graphene) severely impact quantum yield and electron-hole recombination, limiting its suitability in optoelectronics. Herein, a bottom 2D-graphene directly on the Ge substrate by chemical vapor deposition (CVD), a middle 3D-graphene is synthesized in-situ using 2D-graphene as the buffer layer via plasma-enhanced chemical vapor deposition (PECVD). A top 2D-graphene is transferred to 2D/3D-graphene/Ge by thermal release tape (TRT) technology to form a vertical 2D/3D/2D graphene sandwich cavity on the Ge substrate. The bottom 2D-graphene layer can not only perform as an interfacial layer for the in-situ preparation of 3D-graphene but also increase the electrical conductivity of the interface and advance the character of the Schottky junction formed between 3D-graphene/Ge, thereby improving the photon detection. The fabricated photodetector exhibits outstanding characteristics at a 1550 nm wavelength, with a high responsivity of 1.4 A/W and detectivity of 1.1 × 10¹⁴ Jones. This is due to the enhanced light absorption of the sandwich cavity and a high-quality interface layer (bottom 2D-graphene). The results reveal that this vertical 2D/3D/2D graphene sandwich architecture will facilitate the development of graphene-based NIR detection.