Schottky Barrier Height Modification of Graphene/Ge by Al2O3 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 (2-nm-thick Al2O3) 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^{{11}} cm \cdot Hz ^{\text {1/2}} \cdot \text{W}^{-{1}} and 4.4\times 10^{{11}} cm \cdot Hz ^{\text {1/2}} \cdot \text{W}^{-{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.