Doping-driven electronic and lattice dynamics in the phase-change material vanadium dioxide
Doping-driven electronic and lattice dynamics in the phase-change material vanadium dioxide
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DOI：
10.1103/physrevb.102.115148
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发表时间：
2020-09
影响因子：
3.7
通讯作者：
K. Appavoo;J. Nag;Bin Wang;W. Luo;G. Duscher;E. A. Payzant;M. Sfeir;S. Pantelides;R. Haglund
中科院分区：
文献类型：
--
作者：
K. Appavoo;J. Nag;Bin Wang;W. Luo;G. Duscher;E. A. Payzant;M. Sfeir;S. Pantelides;R. Haglund
掺杂通常被理解为在半导体中包括额外的正或负电荷载流子的策略，从而调节费米能级并改变其在平衡极限中的电子性质。然而，因为掺杂剂也耦合到主体中的所有微观自由度，所以它们也可能改变母体材料的非平衡动力学性质，特别是在大掺杂剂浓度下。在这里，我们展示了如何替代掺杂钨在1原子。%水平改变相变材料二氧化钒的复杂电子和晶格动力学。使用飞秒宽带光谱，我们比较了最宽的波长和时间范围内尚未报道的原始和钨掺杂的$\mathrm{V}{\mathrm{O}}_{2}$外延薄膜的动态。我们表明，钨原子的主机晶格耦合修改早期的电子-声子动力学的飞秒时间尺度上，以一种违反直觉的方式改变的ps到ns的相变的光学签名。密度泛函理论正确地捕捉原始和W-掺杂$\mathrm{V}{\mathrm{O}}_{2}$之间的焓差，并显示掺杂剂如何软化临界V-V声子模式，同时引入新的声子模式，由于W-V键。虽然替代掺杂提供了控制相变材料的开关阈值和对比度的强大方法，但确定掺杂剂如何动态改变宽带光学响应对于光电子学同样重要。
Doping is generally understood as a strategy for including additional positive or negative charge carriers in a semiconductor, thereby tuning the Fermi level and changing its electronic properties in the equilibrium limit. However, because dopants also couple to all of the microscopic degrees of freedom in the host, they may also alter the nonequilibrium dynamical properties of the parent material, especially at large dopant concentrations. Here, we show how substitutional doping by tungsten at the 1 at. % level modifies the complex electronic and lattice dynamics of the phase-change material vanadium dioxide. Using femtosecond broadband spectroscopy, we compare dynamics in epitaxial thin films of pristine and tungsten-doped $\mathrm{V}{\mathrm{O}}_{2}$ over the broadest wavelength and temporal ranges yet reported. We demonstrate that coupling of tungsten atoms to the host lattice modifies the early electron-phonon dynamics on a femtosecond timescale, altering in a counterintuitive way the ps-to-ns optical signatures of the phase transition. Density functional theory correctly captures the enthalpy difference between pristine and W-doped $\mathrm{V}{\mathrm{O}}_{2}$ and shows how the dopant softens critical V-V phonon modes while introducing new phononic modes due to W-V bonds. While substitutional doping provides a powerful method to control the switching threshold and contrast of phase-change materials, determining how the dopant dynamically changes the broadband optical response is equally important for optoelectronics.