基于非对称纳米间隙电极的二维热电子光探测器研究

In recent years, it is a hot research topic in the field of photoelectronic devices that the hot electrons induced by plasmonic nano-stucture are used to extend the photodetector’s detecting wave range and improve their photoelectric performance. However, the current research mostly focused on the enhancement of light absorption induced by the plasmonic resonance structure, and did not consider how to realize the fast and efficient collection for hot electrons. In this project, a new type of hot electron photodetector integrated the advantages of light absorption and collection of hot electorns is proposed. Single/few layer of MoS2 is used as device material to enhance the internal optical gain. Due to the nonequilibrium photo-current produced by asymmetric structure, the device is a passive detector. Narrowed to nanometer scale to reduce hot electrons’ scattering loss, metal electrode gaps focus light and increase collection speed and efficiency. Nano-gap electrodes with high resolution are prepared by electron beam lithography process and the key technology will be studied. We will investigate the limiting factors for the collecting speed and efficiency of hot electrons and clarify their physical mechanisms. The working principle of asymmetric nano-gap electrodes and its role in the improvement of device performance will be studied. The physical mechanisms of the contact of Au electrodes and MoS2 will be clarified. We will fabricate and test these devices by experiments. It is expected to get hot electron photodetectors with ultra-fast speed, high sensitivity and wide-band through this project.

利用等离激元纳米结构诱导热电子以扩展光探测器的工作波段、提升光电性能是近年光电器件领域的研究热点。但目前的研究大多聚焦于利用等离激元共振增强器件光吸收，并没有考虑如何实现热电子的高效收集。本项目拟提出一种在光吸收和热电子收集两方面兼具优势的光探测器件：采用单层/少层MoS2作为器件材料以提升内部光电增益；非对称电极能产生非平衡光生电流，实现无源光电响应;金属电极间隙缩小至纳米尺度以降低热电子的输运损耗，在聚焦入射光的同时大幅提高热电子收集速度与效率。探索利用电子束曝光工艺制备高分辨率纳米间隙电极的关键技术;从物理机制上阐明制约热电子收集效率的关键因素；阐明非对称纳米间隙电极的工作机理及其对热电子收集的提升作用；阐明金属电极与单层/少层MoS2材料接触的物理机制；完成器件的实验制备及性能测试。本项目将有望获得超快、高灵敏度、宽波段的热电子光探测器。

热电子光探测器可以使硅基器件无需键合或外延低带隙半导体而实现近红外光探测。本项目的旨在结合二维材料和硅基的优势，通过缩短热电子在半导体中的输运距离，提高器件对光的吸收转化等方式提高器件的光电响应率，并研究器件的物理机理，达到对此类器件的深入理解，为器件设计提供指导。本项目开展实验和理论研究，主要取得的研究成果有：1. 针对器件光吸收率低的问题，采用透明二维材料作为光电极，有效提升了光吸收率，器件响应率的峰值出现在波长为1310 nm处，值为3.75 mA/W。当波长为1550 nm时，响应率的值为1.58 mA/W。2. 为了缩短热电子的输运距离，将纳米金属电极埋入硅基，增大了热电子的界面发射锥角，使热电子的收集效率有效提升，从而使器件的光电响应率得到很好提升。3. 利用二维超材料的滤光特性，设计了圆偏振光探测器，器件对于左、右旋圆偏振光有较大的光响应率差异。4.结合嵌入式电极和二维材料的优势，设计了嵌入式二维热电子光探测器，在1550 nm波长处获得巨大的光响应率差值，其差值为21 mA W−1。5. 提出一种新型的自供电基于二维手性超材料的硅基圆偏振光探测器。该器件利用二维手性超材料电极实现对左、右旋圆偏振光的差异性吸收，通过判断输出电流的方向以实现左、右旋圆偏振光的鉴别。这些研究成果证明二维热电子光探测器在光通信、仿生学、热成像等领域有很重要的应用价值。