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.

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相变材料二氧化钒中掺杂驱动的电子和晶格动力学

掺杂通常被理解为一种在半导体中包括其他正或负电荷载流子，从而调节费米能级并在平衡极限内改变其电子性能的策略。但是，由于掺杂剂还耦合到主体中的所有微观自由度，因此它们也可能改变母体材料的非平衡动力学性质，尤其是在大掺杂剂浓度下。在这里，我们展示了如何在1 at处进行钨的置换掺杂。％水平改变了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，我们比较了原始和掺钨外延薄膜的动力学$\mathrm{V}{\mathrm{Ø}}_2$尚未报道过的最宽的波长和时间范围。我们证明钨原子耦合到主晶格在飞秒的时间尺度上修改了早期的电子声子动力学，以一种反直觉的方式改变了相变的ps到ns光学特征。密度泛函理论正确地捕获了原始和W掺杂之间的焓差$\mathrm{V}{\mathrm{Ø}}_2$并展示了掺杂剂如何软化临界VV声子模式，同时由于WV键引入了新的声子模式。尽管替代掺杂提供了一种控制相变材料的开关阈值和对比度的有效方法，但确定掺杂剂如何动态改变宽带光响应对光电技术同样重要。