Optimization of metal-to-insulator phase transition properties in polycrystalline VO2 films for terahertz modulation applications by doping
Optimization of metal-to-insulator phase transition properties in polycrystalline VO2 films for terahertz modulation applications by doping
复制标题
通过掺杂优化多晶 VO2 薄膜中金属-绝缘体相变特性，用于太赫兹调制应用
DOI：
10.1039/c7tc05536f
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发表时间：
2018-02-21
影响因子：
6.4
通讯作者：
Jiang, Yadong
中科院分区：
文献类型：
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作者：
Ji, Chunhui;Wu, Zhiming;Jiang, Yadong
二氧化钒（VO 2）由于其众所周知的金属-绝缘体相变（MIT），是实现太赫兹（THz）光调制器件的一个有希望的候选者。此外，VO 2在调制器件上的应用需要与其光学性质的显著变化相关联的窄的滞后宽度，这在Si基多晶VO 2膜中是相当具有挑战性的。本文通过在多晶VO 2薄膜中掺杂高价金属离子（W ~（6+）或Nb ~（5+）），观察到薄膜的磁滞宽度变窄，相变温度降低。有趣的是，这些掺杂的VO 2薄膜总是保持高的太赫兹场调制深度，尽管低的相变温度导致使用的W或Nb掺杂剂。综上所述，在高纯硅衬底上沉积的具有6.5%Nb掺杂的优化的VO 2薄膜表现出最好的MIT特性，其巨场THz调制深度为62.5%，小的滞后宽度低至4.8摄氏度，相变温度低至31.1摄氏度左右，这对于实际应用是非常优异的。在此基础上，综合研究了W和Nb掺杂对多晶VO 2薄膜的微结构和MIT特性的影响。掺杂Nb 5+和W 6+离子通过类似的机制具有类似的效果。此外，THz调制能力和相变温度之间的良好平衡与掺杂薄膜的高结晶度有关。退火过程可能在这种特殊情况下起关键作用。这些结果表明，采用我们独特的制备方法可以有效地调控多晶VO 2薄膜的MIT性能，为设计和制备具有合适MIT性能的VO 2薄膜提供了一种可行的解决方案。
Vanadium dioxide (VO2), due to its well-known metal-insulator phase transition (MIT), is a promising candidate to realize optical modulation devices operating at terahertz (THz) frequencies. Moreover, the application of VO2 on modulation devices requires a narrow hysteresis width associated with a significant change in its optical properties, which is quite challenging in Si-based polycrystalline VO2 films. In this paper, by doping high-valence metal ions (W6+ or Nb5+) into polycrystalline VO2 films, a narrowed hysteresis width and a decreased phase transition temperature are observed. Intriguingly, these doped VO2 films always maintain a high THz field modulation depth despite the low phase transition temperature resulting from the usage of either W or Nb dopants. To sum up, the optimized VO2 film with 6.5% Nb doping deposited on high-purity silicon substrates exhibits the best MIT characteristics with a giant field THz modulation depth of 62.5%, a small hysteresis width down to 4.8 degrees C and a low phase transition temperature of around 31.1 degrees C, which is very excellent for practical applications. Furthermore, we synthetically investigate the influences of W and Nb doping on the microstructures and MIT characteristics of the polycrystalline VO2 films. Doping Nb5+ and W6+ ions has similar effects through a similar mechanism. In addition, the excellent balance between the THz modulation ability and phase transition temperature is related to the high crystallinity degree of the doped films. The annealing process may play a key role in this peculiar case. These results show that the excellent MIT properties of the polycrystalline VO2 films can be effectively tailored by our distinctive preparation method, which provides a feasible solution to the design and fabrication of VO2 films with suitable MIT properties for THz devices.