纳米线合成的最新进展使晶体相的实现成为可能,只有在极端条件下才能达到本体。即,高温和/或高压。对于IV族半导体,这意味着可以使用六方相SixGe1-x纳米结构(具有2H对称类型)。预测其对于x具有高达0.5-0.6的直接带隙,并且将允许实现容易处理的光电器件。利用GaAs和Ge之间的准完美晶格匹配,我们合成了x高达0.59的六方相GaAs-Ge和GaAs-SixGe1-x核壳纳米线。通过组合位置-,极化-,和激发波长相关的μ-拉曼光谱研究与第一性原理计算,我们探索这些材料的完整晶格动力学。特别是,通过获得声子模式的频率成分校准曲线,研究声子模式对纳米线位置的依赖性,并利用共振拉曼条件来揭示晶格振动和电子跃迁之间的耦合,我们为深入了解2H-SixGe1-x纳米结构合金的声子特性及其与晶体质量的关系奠定了基础,化学成分,和电子能带结构。
Recent advances in nanowire synthesis have enabled the realization of crystal phases that in bulk are attainable only under extreme conditions, i.e., high temperature and/or high pressure. For group IV semiconductors this means access to hexagonal-phase SixGe1-x nanostructures (with a 2H type of symmetry), which are predicted to have a direct band gap for x up to 0.5-0.6 and would allow the realization of easily processable optoelectronic devices. Exploiting the quasi-perfect lattice matching between GaAs and Ge, we synthesized hexagonal-phase GaAs-Ge and GaAs-SixGe1-x core-shell nanowires with x up to 0.59. By combining position-, polarization-, and excitation wavelength-dependent μ-Raman spectroscopy studies with first-principles calculations, we explore the full lattice dynamics of these materials. In particular, by obtaining frequency-composition calibration curves for the phonon modes, investigating the dependence of the phononic modes on the position along the nanowire, and exploiting resonant Raman conditions to unveil the coupling between lattice vibrations and electronic transitions, we lay the grounds for a deep understanding of the phononic properties of 2H-SixGe1-x nanostructured alloys and of their relationship with crystal quality, chemical composition, and electronic band structure.