基于回音壁模式的热电子光电转换研究

Hot-electron photoconversion based on internal photoemission effect is attracting more and more attention due to the utilization of photons with energy below the band edge of the semiconductor materials. However, due to the lack of the effective light and carrier management strategies, the photoconversion efficiency of the hot-electron device is extremely low. Although the metallic nanostructures can promote the hot-electron generation by excitating surface plasmons, they are highly demanding on the nanofabrication technology and time-consuming; meanwhile, for the planar system, the involved thick metal film and numerous dielectric layers lead to a low photoconversion efficiency and throughput. In this project, we propose a novel hot-electron photoconversion system based on the optical whispering gallery mode. By exciting the whispering gallery mode in the dielectric nanospheres, the incident light can be coupled into the ultrathin metallic film to improve the hot-electron generation, transport, and injection efficiency simultaneously. The main contexts of the research are listed as follows: designing the nanosphere arrays to excite the whispering gallery mode and investigating how to control the resonance wavelength and intensity to realize the polarization-insensitive, wide-angle narrowband/broadband photoresponse. Then, constructing the comprehensive hot-electron generation, transport and injection model to predict and optimize the photoconversion performance of the hot-electron device. Finally, carrying out the device fabrication, characterization and performance test to achieve the high-efficiency, easy-fabrication and large-scale hot-electron device.

基于内光电效应的热电子光电转换可以收集能量低于半导体带隙的光子，引起了科研人员的广泛关注。然而，由于缺少有效的光电管理策略，器件转换效率极低。虽然表面等离子共振可以提高热电子产生率，但是复杂的金属微纳结构对纳米加工技术要求高且成本昂贵；同时，平面系统由于涉及较厚的金属和较多的电介质层，器件转换效率和成品率不高。本项目提出基于光学回音壁模式的热电子光电转换体系。通过在电介质纳米球中激发光学回音壁模式将入射光耦合进超薄金属薄膜中提高热电子产生、输运和注入效率。研究内容包括：设计激发光学回音壁模式的电介质纳米球阵列结构；分析器件结构对回音壁模式共振波长和强度的调控，实现对角度和入射光偏振不敏感的高效窄带/宽带光学响应；构建完善的热电子产生、输运和注入模型实现对热电子器件电学性能的准确预测和深度调控。最后开展实验、器件表征和光电转换性能测试，实现高效、易制备、大面积的热电子器件。

本课题研究的热载流子光电探测器通过金属与半导体接触形成的肖特基结来收集金属吸收光子后产生的高能量热载流子，拓展了传统半导体光电探测器的可探测波长范围。然而，较低的热载流子光电转换效率和复杂的金属微纳结构导致器件成本高和难以大面积制备等问题，阻碍了热载流子红外光电探测器的实际应用。本研究基于第一性原理计算和蒙特卡罗模拟，研究了二维层状过渡金属碳、氮化物在热载流子器件中的应用；研究了不同应变(拉伸和压缩应变)对金属电子结构的调控和对热载流子产生、传输性能的影响，探索了不同应变下热载流子器件的注入效率；从理论和实验上提出基于平面双层结构的热电子光电探测器。其在光学上可以实现光学完美吸收以提高热电子产生率，在电学上热电子越过肖特基结被收集产生光电流，探讨了双层系统在宽带热载流子光电探测中的应用；在基于等离激元纳米结构的热电子光电探测器理论和研究方面：提出并制备了基于超表面结构、金/硅纳米碗、纳米线和纳米锥的热载流子光电探测器，分别在可见波段到近红外波段都可以实现超宽带、偏振不敏感的广角高吸收和热载流子光电探测，理论探测波长极限可以到2.5 μm。并且，从实验上验证了在单像素光电成像领域中的应用；最后对热载流子光电探测研究的三个重要方面进行了详细介绍和展望，包括金属微纳结构中的热载流子产生、传输和注入过程；热载流子器件的热力学损耗分析以及新材料、新结构实现器件性能的突破；热载流子光电探测器在纳米显微成像、圆偏振光检测和折射率传感等领域的应用。