Schottky Barrier Height Modification of Graphene/Ge by Al $_{\text{2}}$ O $_{\text{3}}$ Interfacial Layer and Au Nanoparticles for High-Gain Short-Wavelength Infrared Photodetectors

The metal/germanium (Ge) photodetectors have garnered significant attention for their potential applications in ON-chip optoelectronics. However, the severe Fermi-level pinning effect (FLPE) on the Ge surface makes it difficult to suppress dark current and improve photoresponsivity. To address these issues, an ultrathin dielectric layer ( $\text{2}$ -nm-thick Al $_{\text{2}}$ O $_{\text{3}}$ ) is introduced between metal and Ge to mitigate the FLPE. Additionally, monolayer graphene (Gr) decorated with Au nanoparticles (NPs) serves as a transparent electrode to enhance the responsivity of the photodetector. The responsivities of the Au NPs decorated Gr/Ge junction photodetectors are significantly improved to 7528 and 7115 A/W at 1310 and 1550 nm, respectively, under dim light illumination at room temperature. The corresponding specific detectivities reach up to 4.59 $\times$ 10 $^{\text{11}}$ cm $\cdot$ Hz $^{\text{1/2}}$ $\cdot$ W $^{-\text{1}}$ and 4.4 $\times$ 10 $^{\text{11}}$ cm $\cdot$ Hz $^{\text{1/2}}$ $\cdot$ W $^{-\text{1}}$ , respectively. These results demonstrate that the combination of 2-D and 3-D materials is an effective strategy for high-performance photodetectors working in short-wave infrared (SWIR) bands at a low cost.