School of Optoelectronic Information, State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China , Chengdu 610054, P.R. China.
School of Science, Shandong University of Technology , ZiBo, Shandong 255049, P.R. China.
ACS Appl Mater Interfaces. 2016 May 11;8(18):11842-50. doi: 10.1021/acsami.5b12417. Epub 2016 May 2.
Due to the insulator-metal transition (IMT) performance covering the full terahertz (THz) band, VO2 films were extensively investigated as an excellent candidate for modulating, switching, and memory devices. However, some remarkable absorption peaks owing to the infrared-active phonon modes suppressed the films' modulation ability and restricted the films' application in high THz frequency. Here we prepared Al-doped VO2 films on (111) directional silicon substrate, which rapidly counteracted the absorption peak and exhibited widely modulating properties. Al dopants introduced into the films brought a significant shift to high frequency in Raman spectra. The result was attributed to the effect of modifying VO2 crystal, leading the V-O bond to be strained more intensively, contracting the distance of the V-V dimers. All the Raman results indicated an oxidation effect by Al doping. However, the XPS results showed a valence reduction of the vanadium element, which was caused by the valence difference between V and Al atoms. In addition to the surface morphology characterization, the IMT properties of the shrinkage of hysteresis width and resistance variations in both electrical and THz optical aspects have been systemically analyzed. An additional difference is that the temperature of the optical transition behaves lower than the electrical transition observed, which resulted from the mechanism of transition propagation and boundary barriers.
由于其在整个太赫兹（THz）波段的绝缘体-金属转变（IMT）性能，VO2 薄膜作为一种出色的调制、开关和存储器件候选材料得到了广泛的研究。然而，由于红外活性声子模式引起的一些显著吸收峰抑制了薄膜的调制能力，并限制了其在高 THz 频率下的应用。在这里，我们在（111）方向硅衬底上制备了掺 Al 的 VO2 薄膜，它能迅速抵消吸收峰并表现出广泛的调制性能。Al 掺杂剂引入薄膜后，拉曼光谱中的峰发生了显著的向高频移动。这归因于修饰 VO2 晶体的作用，使 V-O 键更加剧烈地受到应变，V-V 二聚体的距离缩短。所有拉曼结果都表明了 Al 掺杂的氧化效应。然而，XPS 结果显示钒元素的价态降低，这是由于 V 和 Al 原子之间的价态差异所致。除了表面形貌表征外，我们还系统地分析了电和太赫兹光学方面迟滞宽度收缩和电阻变化的 IMT 特性。一个额外的区别是，光学跃迁的温度表现低于观察到的电跃迁温度，这是由于跃迁传播和边界势垒的机制所致。
