用于高效光能收集的超薄纳米器件及其光电性能调控

When the absorptive materials are scaled down to ultra-thin dimensions (inculding individual layers of atomic crystal planes), their light-matter interactions (e.g. optical absorption, energy conversion enfficiency, nonlinear optical response, etc.) are weak.That is why in most thin-film energy harvesting/conversion applications, there is a trade-off between optical absorption and thickness of s emiconductor materials. In this project, we will develop a fundemantal strategy to enhance the light-matter interaction of ultra-thin films (i.e. sub-5-nm-thick Ge, Si or SiGe films) based on strong interference effect in planar nanocavities, and overcome the limitation between the optical absorption and film thickness of energy harvesting/conversion materials without increasing the thickness of the films. By inserting a lossless spacer layer (e.g. SiO2, Al2O3 , HfO2 or TiO2 films) between the ultra-thin absorbing film and the highly reflective metal film, the optical absorption in the ultra-thin semiconductor layer can be enhanced significantly. This principle is quite general and will be applied to explore the spectrally tunable absorption enhancement of various ultra-thin absorbing semiconductor materials, which will create new regimes of optical physics and photon-energy collection applications. The dimension, material, microscopic crystal structure of the nanocavity will be characterized in detail to reveal its correlation with the angle and polarization state of the incident light. The relation between optical absorption and the carrier generation, transportation and collection will be explored, including the surface defect state effect in these ultra-thin semiconductor layers. We will focus on developing the controllable fabrication and characterization methods for the proposed nanocavity enhanced ultra-thin films, and exploring the feasibility of these super absorbing ultra-thin films for improved photo-detection and energy collection/conversion devices. Accordingly, it is expected to have significant implications in both theory and application in the near future.

当薄膜厚度小到有限原子层时,光与薄膜的相互作用,如光吸收,能量转化效率,非线性光响应等就明显减弱。因此对光能收集和能量转换的功能器件而言,减小半导体薄膜厚度和提高光吸收率之间存在矛盾。本项目致力于研究在不改变薄膜材料厚度的条件下大幅增强超薄材料的光吸收的器件结构,提出在5nm以下的Ge、Si或其合金膜和高反射金属层(Au,Ag,Al,Cu)之间加入相位补偿层(SiO2,Al2O3,HfO2,TiO2),形成三层器件结构;研究其吸收增强和波峰调控效应,系统探讨超薄吸收材料强干涉效应的形成和器件应用的条件;揭示纳米腔结构的尺度,材料组分,晶态结构,外部入射光的角度和偏振态与光吸收及光生载流子传输收集之间的关系;阐明材料界面问题作用于光吸收和载流子输运的物理机制;建立超薄半导体光吸收结构的可控制备和表征手段,为超薄膜(包括单原子层厚度)器件的能效提升提供思路和实证，具有理论和实际应用价值.

金属纳米材料，由于有着特殊的物理、化学性质，在光学领域有着很好的应用前景，得到了广泛的关注。金属纳米颗粒材料，在光学检测、纳米涂料、光电催化、光学成像、传感等领域有很大的应用价值。薄膜材料在各种光学仪器中几乎是不可分离的部分。随着人类科技水平的提高，金属纳米颗粒材料、薄膜材料的工艺控制、结构设计等方面得到了巨大的提升。通过结构设计，来提高纳米腔超薄膜的光吸收性能是目前的一个研究的热点，这种特殊光电性能的器件在光电检测、光能收集器件领域有着重要的应用空间。本项目利用一种低成本的制备方法，将金属纳米颗粒作为一层材料，并融合到传统的薄膜干涉结构中，利用这两种结构相结合来调控整个体系的光学性质。通过调节MIM三层结构薄膜的中间介质层厚度以及表面颗粒的形貌、尺寸及材质，来改变整个结构的光吸收能力，从而使薄膜实现不同的结构色。在调制结构色的基础上，利用二次退火的方法，在三层结构薄膜体系中引入金银混合颗粒表面，提高体系光吸收能力并作为表面增强拉曼（SERS）的衬底。由于表面存在混合金属颗粒以及结合了MIM三层结构的设计优化，使得这种SERS衬底有比较理想的增强因子、均匀性、使用寿命等性质，在环境检测、食品安全、毒品检测等领域有着很好的实际应用价值。