Germanium Nanostructures for Efficient Silicon-Compatible Optoelectronics

该项目由材料研究部（DMR）的电子和光子材料计划（EPM）和电气、通信和网络系统部（ECCS）的能源、电力和自适应系统计划（EPAS）共同资助。技术描述：基于受限锗量子点和锗/硅量子线的高效光电活性材料，有望增强对芯片兼容光电探测器和宽带吸收太阳能电池有用的光转换机制。该项目重点研究两类相互关联的光电材料和器件：(1)用于高效光电探测器的紧密排列的Ge量子点阵列和(2)用于串联太阳能电池的Ge/Si异质阳极线。锗量子点的材料性质（如浓度、结晶度和表面钝化）与光电功能直接相关，并对其进行了优化，以提高光探测速度，同时保持高响应性。利用时间分辨测量以及充电和量子点间跳变的理论建模研究了响应时间和增益机制。对于第二类材料和器件，使用蒸汽-液-固技术生长Ge/Si纳米线以克服晶格失配限制。异质纳米线的输运和光响应与纳米线直径、长度、掺杂和成分有关，并用于预测具有提高光谱覆盖和降低反射率的密集纳米线阵列的集体行为。为了提高光电转换效率，我们进行了模拟以匹配锗和硅段的短路电流。非技术描述：这个研究项目是关于锗基纳米结构中的光-物质相互作用，包括量子点和量子线。这些纳米结构结合了吸引人的物理特性，使得在纳米尺度上更有效的光-物质相互作用成为可能。具体来说，该项目寻求将这些纳米材料用于更高效的光电探测器和宽带太阳能电池。这项研究在布朗大学的课堂内外都产生了教育影响。它包括布朗大学的教师和研究生与洛斯阿拉莫斯国家实验室的科学家在纳米线生长方面的长期合作。本科生也参与了部分研究。此外，以太阳能为基础的K-12推广活动得到扩大，当地高中生参加实验室夏季研究。

This project is jointly funded by the Electronic and Photonic Materials Program (EPM) in the Division of Materials Research (DMR) and the Energy, Power, and Adaptive Systems Program (EPAS) in the Division of Electrical, Communications and Cyber Systems (ECCS).Technical Description: Efficient optoelectronic active materials, based on confined germanium quantum dots and germanium/silicon quantum wires, promise enhanced photoconversion mechanisms useful for chip-compatible photodetectors and solar cells with broadband absorption. This project focuses on two interrelated classes of optoelectronic materials and devices: (1) a close-packed array of Ge quantum dots for high-efficiency photodetectors and (2) Ge/Si heteronanowires for tandem solar cells. Materials properties of Ge quantum dots (such as concentration, crystallinity and surface passivation) are directly correlated to optoelectronic functionalities and optimized to improve the photodetection speed while retaining high responsivity. The response time and gain mechanisms are studied using time-resolved measurements as well as theoretical modeling of charging and inter-quantum-dot hopping. For the second class of materials and devices, the Ge/Si nanowires are grown using the vapor-liquid-solid technique to overcome lattice mismatch limitations. The transport and optical response of individual heteronanowires are correlated with nanowire diameter, length, doping and composition, and are used to predict the collective behavior of dense nanowire arrays with improved spectral coverage and reduced reflectivity. Simulations are performed to match the short-circuit currents in the Ge and Si sections in order to achieve enhanced photoconversion efficiency.Non-technical Description: This research project is on light-matter interactions in germanium-based nanostructures, including quantum dots and quantum wires. These nanostructures combine attractive physical properties enabled by more efficient light-matter interaction at the nanoscale. Specifically, the project seeks to use these nanomaterials for higher-efficiency photodetectors and broadband solar cells. The research has educational impact in and out of the classroom at Brown University. It includes long-term collaboration between faculty and graduate students at Brown University and scientists at the Los Alamos National Laboratory, on nanowire growth. Undergraduates also work on parts of the research. In addition, solar energy-based K-12 outreach activities are expanded and local high-school students participate in laboratory summer research.