电场激励条件下VO2薄膜非均匀相变的演化机制及相变速度调控研究

The ultrafast semiconductor-metal phase transition of vanadium dioxide (VO2) is the foundation for its application in high-speed optoelectronic devices. In order to improve the transition speed of electric field triggered phase transition in VO2 film, we propose to study the inhomogeneous phase transition phenomenon in the VO2 film triggered by electric field, and then improve this inhomogeneous for achieving faster phase transition speed in the film. We will investigate the formation and evolution mechanism of the inhomogeneous phase transition induced by electric field, as well as the correlation between this inhomogeneous phase transition and the transition speed. Then we will prepare the VO2 films with different microstructure, stoichiometry (the ratio of +4 valence vanadium in the film, single doping or multiple doping) and internal stress, and elucidate their effects on the inhomogeneous phase transition in the film. Moreover, we will regulate and optimize these factors, aimed at realizing much faster transition speed in the VO2 film. Our research may provide significant insights for the application of VO2 film in ultrafast terahertz devices, such as switching, modulation and memory.

VO2的超快半导体-金属相转变速度是其在高速光电器件中应用的基础。针对目前VO2薄膜的相变速度快慢不一，尤其是电致相变速度过慢的问题，提出研究外加电场条件下VO2薄膜在微观尺度上的非均匀相变现象，并计划通过改善薄膜的相变均匀性，提高其相变速度。本项目将研究电场激励条件下VO2的非均匀相变形成和演化机制，以及这种相变非均匀性与薄膜相变速度的关联性；系统分析微观结构、化学组成（+4价钒氧化物比例、元素单一掺杂或复合掺杂条件）和内应力等对薄膜相变均匀性的影响规律，并在此基础上，通过对VO2薄膜微观结构参数、组成和内应力状态的可控调整和综合优化设计，改善其相变均匀性，从而提高薄膜的相变速度，进而为VO2薄膜在THz波开关、调制、存储等功能器件领域的应用提供基础，促进其发展。

VO2的超快半导体-金属相转变速度是其在高速光电器件中应用的基础。针对现有研究报道中VO2薄膜的相变速度快慢不一，尤其是电致相变速度过慢的问题，本项目研究外加电场条件下VO2薄膜的非均匀相变现象，并计划通过改善薄膜的相变均匀性，提高其相变速度。该工作研究了薄膜电致相变的机理，发现在外加电场下VO2薄膜发生半导体态-金属态的陡然跳变，以及薄膜金属相逐步增加直至相变完成的非均匀相演化特征，结合临界电流理论阐释了薄膜的相变激发电压。从材料热力学角度阐明了VO2薄膜的生长模式，为薄膜的微观结构调控提供了理论和实验基础；通过材料设计制备，系统分析了VO2薄膜的致密度、晶粒尺寸、掺杂组成和衬底条件对其相变过程的影响规律。采用太赫兹泵浦-探测技术研究了VO2薄膜的超快相变现象，提出VO2薄膜的非均匀相变特征及其对相变速度的影响规律。另外，还发现VO2薄膜相变过程中电阻变化并与衬底实现阻抗匹配的现象，可以在无需薄膜相变完成的条件下，实现高效光电调控，为提高基于VO2薄膜相变特性的光电器件响应速率提供了一种新思路。本研究可为VO2薄膜相变速度优化及其在动态光电功能器件中的应用提供基础。