柔性3D-石墨烯/鍺異質結，實現380–1850nm超寬帶光電探測

1成果簡介

柔性光電探測器因在可穿戴健康監測、機器人視覺、柔性顯示等領域的廣闊前景，受到學術界和產業界的高度關注。鍺（Ge）作為IV族窄帶隙半導體，在可見-近紅外波段具有優異的光吸收能力，是構建寬帶柔性光電探測器的理想候選材料。然而，超薄柔性鍺薄膜中界面調制與光電響應的物理機制尚不清晰，且柔性器件在持續變形條件下如何保持結構完整性并實現可調控的光電響應仍是重大挑戰。

本文，寧波大學Gang Wang、山東大學郭慶磊教授，中國科學院上海微系統與信息技術研究所薛忠研究員等在《Nano Letters》期刊發表題為"Multiphysics-Coupled Strain Engineering in Flexible 3D-Graphene/Germanium Heterostructures for Broadband Photodetection"的研究論文。研究在4英寸柔性Ge薄膜（~15 μm厚）上成功構建了3D-石墨烯/鍺（3D-Graphene/Ge）異質結，提出了一種多物理場耦合應變工程策略，系統揭示了超薄柔性鍺中界面調制與光電響應的物理機制。該柔性光電探測器展現出以下優異性能：

• 超寬帶響應380–1850 nm（紫外-可見-近紅外全覆蓋）
• 高響應度80.2 A W?1（@1850 nm）
• 高探測率1.2 × 1011 Jones（@1850 nm）
• 超低噪聲2.2 × 10?21 A2 Hz?1
• ??快速響應：上升/下降時間僅164/161 μs
• -3 dB截止頻率1.8 kHz
• 彎曲穩定性>10?次彎曲循環+動態變形后性能穩定
• 
  

研究還將器件成功應用于多光譜成像和可穿戴光電容積脈搏波（PPG）監測（指尖和腕部），展示了其在柔性電子和生物醫學領域的實用化潛力。

2圖文導讀

圖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.

圖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.

圖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.

圖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小結

在本研究中，通過將晶圓級（4英寸）柔性鍺薄膜（約15微米）與原位生長的三維互連石墨烯相結合，構建了一種柔性三維石墨烯/鍺異質結構。這種結構制備出了性能優異、光譜響應寬廣且在機械變形下具有強長期穩定性的柔性光探測器。實驗與模擬結果表明，當垂直取向的3D石墨烯多孔網絡與柔性鍺基板緊密耦合時，可增強光子吸收和載流子傳輸。所制備的柔性光探測器在380至1850 nm波長范圍內表現出穩定的光響應，在1850 nm處的響應度為80.2 A W –1，比探測率達1.2 × 1011瓊斯，低噪聲電流密度為2.2 × 10?21 A2 Hz?1，響應速度達微秒級（tr和tf分別為164和161 μs），且-3 dB截止頻率為1.8 kHz。該研究揭示了柔性異質結構中機械變形、應變梯度與電磁場之間的耦合機制。彎曲引起的應變通過石墨烯的三維結構增強了界面電勢和電場分布，從而產生應變誘導的內建電場。這種增強效應改善了光生載流子的分離，并減少了非輻射復合損耗，確保了在彎曲和加載循環過程中光電性能的穩定性。該器件在經歷反復彎曲循環和長期儲存后，性能退化可忽略不計，彰顯了其機械可靠性和工作穩定性。這種柔性三維石墨烯/鍺光探測器已成功應用于多波長高分辨率成像和精確生理信號采集，實現了從可見光到近紅外光譜范圍內的有效波長分辨、空間定位以及持續的心率動態監測。該研究成果證實了該技術在柔性光電子器件領域的可行性和可靠性，對可穿戴光電子設備、多光譜成像、柔性生物電子學及先進傳感平臺具有重要意義。

文獻：
https://doi.org/10.1021/acs.nanolett.6c00834

來源：材料分析與應用