1成果简介 

        柔性光电探测器因在可穿戴健康监测、机器人视觉、柔性显示等领域的广阔前景，受到学术界和产业界的高度关注。锗（Ge）作为IV族窄带隙半导体，在可见-近红外波段具有优异的光吸收能力，是构建宽带柔性光电探测器的理想候选材料。然而，超薄柔性锗薄膜中界面调制与光电响应的物理机制尚不清晰，且柔性器件在持续变形条件下如何保持结构完整性并实现可调控的光电响应仍是重大挑战。

        本文，宁波大学Gang Wang、山东大学郭庆磊教授，中国科学院上海微系统与信息技术研究所薛忠研究员等在《Nano Letters》期刊发表题为"Multiphysics-Coupled Strain Engineering in Flexible 3D-Graphene/Germanium Heterostructures for Broadband Photodetection"的研究论文。研究在4英寸柔性Ge薄膜（~15 μm厚）上成功构建了3D-石墨烯/锗（3D-Graphene/Ge）异质结，提出了一种多物理场耦合应变工程策略，系统揭示了超薄柔性锗中界面调制与光电响应的物理机制。该柔性光电探测器展现出以下优异性能：

        超宽带响应：380–1850 nm（紫外-可见-近红外全覆盖）⚡ 高响应度：80.2 A W⁻¹（@1850 nm）🎯 高探测率：1.2 × 10¹¹ Jones（@1850 nm）🤫 超低噪声：2.2 × 10⁻²¹ A² Hz⁻¹⏱️ 快速响应：上升/下降时间仅 164/161 μs📊 -3 dB截止频率：1.8 kHz🔄 弯曲稳定性：>10⁴次弯曲循环+动态变形后性能稳定

        研究还将器件成功应用于多光谱成像和可穿戴光电容积脉搏波（PPG）监测（指尖和腕部），展示了其在柔性电子和生物医学领域的实用化潜力。

        2图文导读  

        图1. Fabrication, morphological characterization, and built-in electric field properties of the 3D-graphene/Ge heterojunction. (a) A photograph of a 4-in. wafer-scale flexible Ge film. (b) A digital photograph demonstrating the bendability of the flexible Ge film; the inset presents a cross-sectional SEM image of Ge. (c) A cross-sectional SEM image of the 3D-graphene/Ge heterostructure. (d) Three-dimensional AFM image of the 3D-graphene/Ge heterostructure. (e) Porosity map of 3D-graphene. (f) Raman spectra of the 3D-graphene and Ge before and after integration; the inset shows the contact angle measurement. (g) Surface potential mapping of the flexible 3D-graphene/Ge heterojunction under dark and illuminated conditions. (h) Corresponding surface potential variation profiles. (i) Surface current mapping of the flexible heterojunction under dark and illuminated conditions. (j) Corresponding surface current variation profiles.

        图2. Photoelectric performance of the 3D-graphene/Ge heterojunction photodetector. (a) I–V characteristics of the flexible 3D-graphene/Ge heterojunction photodetector measured at different wavelengths. (b) Frequency-dependent noise current spectrum of the device. (c) Photocurrent response of the device to cyclic variations in incident laser power. (d) Photoresponse of the device under illumination with an 1850 nm laser at different modulation frequencies. (e) Attenuation characteristics of the photocurrent amplitude as a function of modulation frequency. (f) tr and tf of the device. (g) Self-powered photoresponse stability of the device; the inset shows the photocurrent variation over 100 consecutive cycles. (h) Responsivity and specific detectivity of the device at different wavelengths.

        图3. Regulation effects and physical mechanisms of mechanical deformation on the photoelectric performance of the flexible 3D-graphene/Ge heterojunction. (a) A schematic illustration of the 3D-graphene/Ge flexible heterojunction in a stable concave bending state. (b) TCAD-simulated distribution of photogenerated carriers in the flexible heterojunction under concave bending with optical illumination. (c) FDTD-simulated stress distribution and (d) electric field mode distribution of the flexible heterojunction under concave bending at different deformation levels. (e) A schematic diagram of the bending test setup for the flexible heterojunction, indicating the bending radius (r) and bending strain (ε). (f) I–V characteristics of the flexible heterojunction under different strain levels with 1850 nm illumination. (g) The dependence of the responsivity of the flexible heterojunction on bending strain. (h) A macroscopic optical photograph of bare flexible Ge under external bending. (i) Stability of the photoresponse signal of the flexible heterojunction during cyclic bending tests.

        图4. Applications of the 3D-graphene/Ge heterojunction in image sensing and flexible physiological signal monitoring. (a) A schematic illustration of the image sensing test platform. (b) A flowchart of signal processing and feature extraction for multiwavelength photoelectric responses. (c) A schematic diagram of pixel partitioning of the raw data. (d) The mask pattern used for imaging tests (size: 7 mm × 7 mm). (e–h) Photocurrent distribution images acquired by the photodetector under illumination at 780, 980, 1550, and 1850 nm, respectively. (i) The fused and visualized result of multiwavelength image integration. (j) A schematic of the fingertip-wearable testing setup, along with the corresponding heart rate measurement results under (k) resting and (l) postexercise conditions. (m) A schematic illustration of the wrist-based detection configuration, along with the corresponding heart rate measurement results under (n) resting and (o) postexercise conditions.

        3小结 

        在本研究中，通过将晶圆级（4英寸）柔性锗薄膜（约15微米）与原位生长的三维互连石墨烯相结合，构建了一种柔性三维石墨烯/锗异质结构。这种结构制备出了性能优异、光谱响应宽广且在机械变形下具有强长期稳定性的柔性光探测器。实验与模拟结果表明，当垂直取向的3D石墨烯多孔网络与柔性锗基板紧密耦合时，可增强光子吸收和载流子传输。所制备的柔性光探测器在380至1850 nm波长范围内表现出稳定的光响应，在1850 nm处的响应度为80.2 A W –1，比探测率达1.2 × 10¹¹琼斯，低噪声电流密度为2.2 × 10⁻²¹ A² Hz⁻¹，响应速度达微秒级（tr和tf分别为164和161 μs），且-3 dB截止频率为1.8 kHz。该研究揭示了柔性异质结构中机械变形、应变梯度与电磁场之间的耦合机制。弯曲引起的应变通过石墨烯的三维结构增强了界面电势和电场分布，从而产生应变诱导的内建电场。这种增强效应改善了光生载流子的分离，并减少了非辐射复合损耗，确保了在弯曲和加载循环过程中光电性能的稳定性。该器件在经历反复弯曲循环和长期储存后，性能退化可忽略不计，彰显了其机械可靠性和工作稳定性。这种柔性三维石墨烯/锗光探测器已成功应用于多波长高分辨率成像和精确生理信号采集，实现了从可见光到近红外光谱范围内的有效波长分辨、空间定位以及持续的心率动态监测。该研究成果证实了该技术在柔性光电子器件领域的可行性和可靠性，对可穿戴光电子设备、多光谱成像、柔性生物电子学及先进传感平台具有重要意义。

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