Multiphysics-Coupled Strain Engineering in Flexible 3D-Graphene/Germanium Heterostructures for Broadband Photodetection

Flexible photodetectors that maintain structural integrity while offering tunable photoelectric responses under deformation face challenges in material selection. Germanium (Ge) is a promising candidate for its strong absorption in the visible- to near-infrared spectrum, yet the mechanisms of interfacial modulation and photoelectric responses in ultrathin flexible germanium remain poorly understood. This study presents a 3D-graphene/Ge heterostructure on 4 in. flexible Ge thin films (∼15 μm thick). The flexible photodetector demonstrates a stable photoelectric response from 380 to 1850 nm, with a responsivity of 80.2 A W⁻¹ and a detectivity of 1.2 × 10¹¹ jones at 1850 nm. It has low noise (2.2 × 10⁻²¹ A² Hz⁻¹), rapid response times (rise/fall times of 164 and 161 μs), and a -3 dB cutoff frequency of 1.8 kHz. The device remains stable after over 10⁴ bending cycles and dynamic deformation. Practical applications involve multispectral imaging and wearable setups for fingertip and wrist photoplethysmography-based monitoring.