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首页> 美国卫生研究院文献>Proceedings of the National Academy of Sciences of the United States of America >Visualization of carrier dynamics in p(n)-type GaAs by scanning ultrafast electron microscopy
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Visualization of carrier dynamics in p(n)-type GaAs by scanning ultrafast electron microscopy

机译：通过扫描超快电子显微镜观察p（n）型GaAs中载流子动力学

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Four-dimensional scanning ultrafast electron microscopy is used to investigate doping- and carrier-concentration-dependent ultrafast carrier dynamics of the in situ cleaved single-crystalline GaAs(110) substrates. We observed marked changes in the measured time-resolved secondary electrons depending on the induced alterations in the electronic structure. The enhancement of secondary electrons at positive times, when the electron pulse follows the optical pulse, is primarily due to an energy gain involving the photoexcited charge carriers that are transiently populated in the conduction band and further promoted by the electron pulse, consistent with a band structure that is dependent on chemical doping and carrier concentration. When electrons undergo sufficient energy loss on their journey to the surface, dark contrast becomes dominant in the image. At negative times, however, when the electron pulse precedes the optical pulse (electron impact), the dynamical behavior of carriers manifests itself in a dark contrast which indicates the suppression of secondary electrons upon the arrival of the optical pulse. In this case, the loss of energy of material’s electrons is by collisions with the excited carriers. These results for carrier dynamics in GaAs(110) suggest strong carrier–carrier scatterings which are mirrored in the energy of material’s secondary electrons during their migration to the surface. The approach presented here provides a fundamental understanding of materials probed by four-dimensional scanning ultrafast electron microscopy, and offers possibilities for use of this imaging technique in the study of ultrafast charge carrier dynamics in heterogeneously patterned micro- and nanostructured material surfaces and interfaces.
机译：二维扫描超快电子显微镜用于研究原位裂解的单晶GaAs（110）衬底的掺杂和载流子浓度依赖性超快载流子动力学。我们观察到了时间分辨的二次电子的显着变化，具体取决于电子结构中的感应变化。当电子脉冲跟随光脉冲时，在正时二次电子的增强主要是由于能量增益涉及光激发的电荷载流子，这些载流子短暂地分布在导带中，并进一步由电子脉冲促进，与能带一致取决于化学掺杂和载流子浓度的结构。当电子在到达表面的过程中遭受足够的能量损失时，深色对比度将在图像中占主导地位。然而，在负时间，当电子脉冲先于光脉冲（电子撞击）时，载流子的动态行为以暗对比度表现出来，这表明在光脉冲到达时抑制了二次电子。在这种情况下，材料电子能量的损失是由于与受激载流子的碰撞。 GaAs（110）中载流子动力学的这些结果表明，载流子-载流子的散射很强，反映在材料二次电子向表面迁移的过程中。本文介绍的方法提供了对通过二维扫描超快电子显微镜探测的材料的基本理解，并为在研究异质构图的微结构和纳米结构的材料表面和界面中的超快电荷载流子动力学时使用该成像技术提供了可能性。

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