Ultrafast Carrier Dynamics in Individual Silicon Nanowires: Characterization of Diameter-Dependent Carrier Lifetime and Surface Recombination with Pump-Probe Microscopy
Ultrafast Carrier Dynamics in Individual Silicon Nanowires: Characterization of Diameter-Dependent Carrier Lifetime and Surface Recombination with Pump-Probe Microscopy
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DOI：
10.1021/jp502737e
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发表时间：
2014-04-24
影响因子：
3.7
通讯作者：
Papanikolas, John M.
中科院分区：
文献类型：
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作者：
Grumstrup, Erik M.;Gabriel, Michelle M.;Papanikolas, John M.
利用光学泵浦探针显微镜研究了通过气-液-固机制生长的硅纳米线（NW）中的超快载流子动力学。实验实现的高时间和空间分辨率提供了对单个纳米结构的载流子动力学的深入了解。单个纳米线被聚焦到衍射极限点的飞秒泵浦脉冲激发，在结构的局部区域产生光生载流子（电子和空穴）。光激发载流子在相似的时间尺度上经历电子-空穴复合和远离激发点的扩散迁移。载流子群体的演变由延迟探测脉冲监测，该脉冲也聚焦于衍射极限点。当泵浦和探针在空间上重叠时，瞬态信号反映重组和载流子迁移。通过在空间上分离泵浦光束和探测光束，可以直接观察扩散运动，从而能够在一个位置生成载流子并在另一位置检测到载流子。对信号的定量分析可以得出大量单个纳米线的载流子寿命的统计分布。平均而言，寿命与直径成线性正比，与表面介导的复合机制一致。这些结果突出了泵浦探针显微镜定量评估半导体纳米结构中关键复合特征的能力，这对于它们在纳米技术中的实现非常重要。
Ultrafast charge carrier dynamics in silicon nanowires (NWs) grown by a vapor-liquid-solid mechanism were interrogated with optical pump-probe microscopy. The high time and spatial resolutions achieved by the experiments provide insight into the charge carrier dynamics of single nanostructures. Individual NWs were excited by a femtosecond pump pulse focused to a diffraction-limited spot, producing photogenerated carriers (electrons and holes) in a localized region of the structure. Photoexcited carriers undergo both electron-hole recombination and diffusional migration away from the excitation spot on similar time scales. The evolution of the carrier population is monitored by a delayed probe pulse that is also focused to a diffraction-limited spot. When the pump and probe are spatially overlapped, the transient signal reflects both recombination and carrier migration. Diffusional motion is directly observed by spatially separating the pump and probe beams, enabling carriers to be generated in one location and detected in another. Quantitative analysis of the signals yields a statistical distribution of carrier lifetimes from a large number of individual NWs. On average, the lifetime was found to be linearly proportional to the diameter, consistent with a surface-mediated recombination mechanism. These results highlight the capability of pump-probe microscopy to quantitatively evaluate key recombination characteristics in semiconductor nanostructures, which are important for their implementation in nanotechnologies.