太赫兹表面等离子体波在半导体表面的传输特性及其应用研究

Terahertz surface plasmon polaritons (THz SPPs) have the potential for applications in communications, detection and chemical analysis by exploiting their traits of being plasmonic as well as in the THz region. Although THz and SPPs are topics that have been under intense investigation, THz SPPs are just developing in recent years. Propagation lengths of THz SPPs are much longer than that of visible light SPPs propagating in metal, but THz SPPs cannot be confined on the surfaces of metals as visible light SPPs do. It is also impossible to control the propagation lengths of THz SPPs by varying the carrier density of metal. In contrast, the carrier density of semiconductors can be easily changed by varying the temperature and the optical intensity, which inspires us to investigate new THz SPPs modulators based on the carrier density modulation. The modulation effect is associated with the plasma frequency of the semiconductor, which controls the propagation length of the THz SPPs through absorption. In comparison with traditional THz SPPs modulators based on gratings, our new devices have the merits of wide modulation frequency band, large modulation amplitude, high modulation speed and low cost. Moreover, THz SPPs spectroscopy can be explored for the study of plasma frequency measurement, carrier density and surface defects detection. We also highlight the possibility of studying biochemical thin films using THz SPPs spectroscopy. Therefore, we can know more about the transmission characters of THz SPPs propagating in semiconductors through the research of this project. We anticipate to contribute to the development of THz industry of our country by exploring the new applications of THz SPPs.

太赫兹表面等离子体波集太赫兹波与表面等离子体波两者优点于一身，在通讯、检测、分析领域有着广阔的应用前景。与金属表面传输的可见光表面等离子体波相比，太赫兹表面等离子体波的传播距离更长,但金属无法将太赫兹表面等离子体波的能量局域在表面，也无法通过改变载流子浓度对其传输进行调制。本项目通过改变温度、光强等手段调控半导体等离子体频率，从而利用半导体吸收对其上传输的太赫兹表面等离子体波传播距离进行调制。与传统光栅调制的方法相比，它具有调控频带宽、幅度大、速度快、成本低等优点。与此同时，通过研究太赫兹表面等离子体波透射谱还可以测量半导体等离子体频率、检测半导体表面的微小缺陷以及分析生化薄膜的结构成份，这些方法都可以在常温下对很薄的样品进行实时无损精确检测。通过本项目的研究，可以进一步掌握太赫兹表面等离子体波在半导体表面的传输特性，扩展太赫兹表面等离子体波在相关领域的应用，为我国太赫兹产业发展作出贡献。

本项目在理论上完成了对太赫兹表面等离子体波在半导体表面的传播特性的研究，推导了太赫兹表面等离子体波在半导体表面的传播距离以及其在半导体内部和空气中的衰减距离公式，并在此基础上进一步推导了半导体等离子体频率的计算公式，研究了半导体等离子体频率与调制光强的变化关系。在理论工作的基础上，实验中完成了以下工作：（1）通过改变温度、照射光强或两刀片之间的距离调控半导体等离子体频率，从而利用半导体吸收对其上传输的太赫兹表面等离子体波传播距离进行调制，与传统光栅调制的方法相比具有调控频带宽、幅度大、速度快、成本低等优点；（2）构建了太赫兹表面等离子体波时域波谱分析系统，通过该装置对本征半导体InSb的等离子体频率进行测量，300 K温度下的测量结果1.87 THz与实际值1.9 THz基本相当；（3）通过太赫兹表面等离子体波时域波谱分析系统对半导体表面缺陷进行了检测，当半导体表面有缺陷时，太赫兹表面等离子体波时域波谱测量系统所测时域和频域谱信号有明显变化，实验所测最小缺陷尺寸仅为11微米；（4）通过太赫兹表面等离子体波时域波谱分析系统对半导体表面覆盖的生化薄膜样品进行透射波谱分析，实验结果表明当测量对象是厚度仅为自由空间太赫兹波波长约1%的单层洋葱表皮时，表面等离子体波的透射波谱与自由空间太赫兹波透射波谱相比具有更加多的特征吸收峰。以上实验均可在常温下对很薄的样品进行实时无损精确检测。通过本项目的研究，进一步掌握了太赫兹表面等离子体波在半导体表面的传输特性，扩展了太赫兹表面等离子体波在相关领域的应用，为我国太赫兹产业发展作出贡献。