基于表面等离激元微纳结构的热载流子光电转换研究

Nano-optoelectronics is a significant field of science at present. During the progress of the nano-miniaturization and integration of the optoelectronic devices, surface plasmonics (SPs) play an important role. However, the relevant researches are mainly focused on the photonic characteristic of the surface plasmonics. This project will integrate the near-field confinement (subwavelength hot spots) of SPs, high controllability of the metallic nanostructures on the characteristic absorption wavelength, and the tunneling junction effect of ultra-thin dielectric film together; in the meantime, we combine both the photonic and electronic characteristics of SPs together and investigate the excitation, transport and photoelectric conversion of the hot carrier in the plasmonic nanostructures. The main contents of the project are as follows: i) Design the new types of metallic nanostructures and device architectures for exciting surface plasmonics, in which the key point is studying the enhancement, the tunability and the optimization of SPs, and exploring the new excitation modes of hot carrier in the metallic nanostructure; ii) Build a suit of dynamical model to describe completely and systematically the transport process of hot carriers, and thoroughly investigate the inner working mechanism of the device, including carrier diffusion, tunneling effect, and so on; iii) Construct the metallic nanostructures, then fabricate the whole device based on hot carrier and explore the effective approaches of improving the photoelectric conversion efficiency, in order to develop new photoelectric conversion device with proprietary intellectual property rights. The implementation of this project will contribute to unearth the new mechanism of photoelectric conversion in the subwavelength devices, and provide helpful guidance to the high efficiency photoelectric detection and solar energy utilization.

纳米光电子学是当前重大科学领域，在光电子器件纳米化和集成化进程中，表面等离激元（SPs）发挥着重要作用，相关研究集中在SPs的光子学特征及应用。本项目同时考虑SPs的光子学和电子学特征，通过有机整合SPs的近场光学限制（亚波长热点场）、微纳金属结构特征吸收波长的高度可控性以及超薄介质膜的隧道结效应，研究SPs微纳结构中热载流子的激发、输运和光电转换机理以及控制措施。主要内容包括：设计激发SPs的新型微纳金属结构和整体器件架构，重点研究SPs的增强、调控和优化机制，探索光生热载流子的激发新模式；从基本物理场出发透彻研究器件内部载流子的扩散和隧穿等效应，建立一套完整的描述热载流子输运过程的动力学模型；构筑金属微结构和热载流子光电器件，系统研究器件光电转换效率提升的有效途径，研发具有自主知识产权的新型光电转换器件。项目的开展有助于发掘亚波长器件光电转换新机制，为高效光电探测和太阳能利用提供指导。

利用有限元方法建立了全场/散射场电磁模型，精确求解Maxwell方程组获得光和微纳结构的相互作用信息；根据热载流子输运的过程建立了完整的输运模型，实现了精确仿真，为后续器件设计奠定了坚实基础。结合纳米光学的已有研究成果，创新设计微纳结构，提出了若干热载流子探测器结构方案，并优化结构参数和器件性能，并初步开展了前期探索性实验。相对于传统光栅结构，共形热载流子探测器结构不但具有更高的净吸收、光响应度，而且具有更窄的线宽；在可见光波段范围内，共形结构在共振频率下的光响应度为~0.032 mA/W，约为一般光栅探测器（~0.012 mA/W）的2.7倍。利用纳米线径向输运特性，提出同轴热电子收集方案，数值验证了在光通信波段热电子探测器在无偏压条件下光响应度可达~200 nA/mW；在正向偏压0.6V下，光响应度可达~600 nA/mW，理论上较光栅热载流子探测器提升2-3个数量级。通过引入透明导电层作为一端电极，提出两种典型的集成平面热载流子器件，在一维光子晶体和上端金属电极（或多层堆栈）之间形成Fabry–Pérot腔，增加电磁场强度和非对称金属吸收，从而实现光电响应度大幅提升。